perf cpumap: Add new map type for aggregation

[linux-2.6-microblaze.git] / fs / nfsd / vfs.c

// SPDX-License-Identifier: GPL-2.0
/*
 * File operations used by nfsd. Some of these have been ripped from
 * other parts of the kernel because they weren't exported, others
 * are partial duplicates with added or changed functionality.
 *
 * Note that several functions dget() the dentry upon which they want
 * to act, most notably those that create directory entries. Response
 * dentry's are dput()'d if necessary in the release callback.
 * So if you notice code paths that apparently fail to dput() the
 * dentry, don't worry--they have been taken care of.
 *
 * Copyright (C) 1995-1999 Olaf Kirch <okir@monad.swb.de>
 * Zerocpy NFS support (C) 2002 Hirokazu Takahashi <taka@valinux.co.jp>
 */

#include <linux/fs.h>
#include <linux/file.h>
#include <linux/splice.h>
#include <linux/falloc.h>
#include <linux/fcntl.h>
#include <linux/namei.h>
#include <linux/delay.h>
#include <linux/fsnotify.h>
#include <linux/posix_acl_xattr.h>
#include <linux/xattr.h>
#include <linux/jhash.h>
#include <linux/ima.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/exportfs.h>
#include <linux/writeback.h>
#include <linux/security.h>

#ifdef CONFIG_NFSD_V3
#include "xdr3.h"
#endif /* CONFIG_NFSD_V3 */

#ifdef CONFIG_NFSD_V4
#include "../internal.h"
#include "acl.h"
#include "idmap.h"
#endif /* CONFIG_NFSD_V4 */

#include "nfsd.h"
#include "vfs.h"
#include "filecache.h"
#include "trace.h"

#define NFSDDBG_FACILITY                NFSDDBG_FILEOP

/* 
 * Called from nfsd_lookup and encode_dirent. Check if we have crossed 
 * a mount point.
 * Returns -EAGAIN or -ETIMEDOUT leaving *dpp and *expp unchanged,
 *  or nfs_ok having possibly changed *dpp and *expp
 */
int
nfsd_cross_mnt(struct svc_rqst *rqstp, struct dentry **dpp, 
                        struct svc_export **expp)
{
        struct svc_export *exp = *expp, *exp2 = NULL;
        struct dentry *dentry = *dpp;
        struct path path = {.mnt = mntget(exp->ex_path.mnt),
                            .dentry = dget(dentry)};
        int err = 0;

        err = follow_down(&path);
        if (err < 0)
                goto out;
        if (path.mnt == exp->ex_path.mnt && path.dentry == dentry &&
            nfsd_mountpoint(dentry, exp) == 2) {
                /* This is only a mountpoint in some other namespace */
                path_put(&path);
                goto out;
        }

        exp2 = rqst_exp_get_by_name(rqstp, &path);
        if (IS_ERR(exp2)) {
                err = PTR_ERR(exp2);
                /*
                 * We normally allow NFS clients to continue
                 * "underneath" a mountpoint that is not exported.
                 * The exception is V4ROOT, where no traversal is ever
                 * allowed without an explicit export of the new
                 * directory.
                 */
                if (err == -ENOENT && !(exp->ex_flags & NFSEXP_V4ROOT))
                        err = 0;
                path_put(&path);
                goto out;
        }
        if (nfsd_v4client(rqstp) ||
                (exp->ex_flags & NFSEXP_CROSSMOUNT) || EX_NOHIDE(exp2)) {
                /* successfully crossed mount point */
                /*
                 * This is subtle: path.dentry is *not* on path.mnt
                 * at this point.  The only reason we are safe is that
                 * original mnt is pinned down by exp, so we should
                 * put path *before* putting exp
                 */
                *dpp = path.dentry;
                path.dentry = dentry;
                *expp = exp2;
                exp2 = exp;
        }
        path_put(&path);
        exp_put(exp2);
out:
        return err;
}

static void follow_to_parent(struct path *path)
{
        struct dentry *dp;

        while (path->dentry == path->mnt->mnt_root && follow_up(path))
                ;
        dp = dget_parent(path->dentry);
        dput(path->dentry);
        path->dentry = dp;
}

static int nfsd_lookup_parent(struct svc_rqst *rqstp, struct dentry *dparent, struct svc_export **exp, struct dentry **dentryp)
{
        struct svc_export *exp2;
        struct path path = {.mnt = mntget((*exp)->ex_path.mnt),
                            .dentry = dget(dparent)};

        follow_to_parent(&path);

        exp2 = rqst_exp_parent(rqstp, &path);
        if (PTR_ERR(exp2) == -ENOENT) {
                *dentryp = dget(dparent);
        } else if (IS_ERR(exp2)) {
                path_put(&path);
                return PTR_ERR(exp2);
        } else {
                *dentryp = dget(path.dentry);
                exp_put(*exp);
                *exp = exp2;
        }
        path_put(&path);
        return 0;
}

/*
 * For nfsd purposes, we treat V4ROOT exports as though there was an
 * export at *every* directory.
 * We return:
 * '1' if this dentry *must* be an export point,
 * '2' if it might be, if there is really a mount here, and
 * '0' if there is no chance of an export point here.
 */
int nfsd_mountpoint(struct dentry *dentry, struct svc_export *exp)
{
        if (!d_inode(dentry))
                return 0;
        if (exp->ex_flags & NFSEXP_V4ROOT)
                return 1;
        if (nfsd4_is_junction(dentry))
                return 1;
        if (d_mountpoint(dentry))
                /*
                 * Might only be a mountpoint in a different namespace,
                 * but we need to check.
                 */
                return 2;
        return 0;
}

__be32
nfsd_lookup_dentry(struct svc_rqst *rqstp, struct svc_fh *fhp,
                   const char *name, unsigned int len,
                   struct svc_export **exp_ret, struct dentry **dentry_ret)
{
        struct svc_export       *exp;
        struct dentry           *dparent;
        struct dentry           *dentry;
        int                     host_err;

        dprintk("nfsd: nfsd_lookup(fh %s, %.*s)\n", SVCFH_fmt(fhp), len,name);

        dparent = fhp->fh_dentry;
        exp = exp_get(fhp->fh_export);

        /* Lookup the name, but don't follow links */
        if (isdotent(name, len)) {
                if (len==1)
                        dentry = dget(dparent);
                else if (dparent != exp->ex_path.dentry)
                        dentry = dget_parent(dparent);
                else if (!EX_NOHIDE(exp) && !nfsd_v4client(rqstp))
                        dentry = dget(dparent); /* .. == . just like at / */
                else {
                        /* checking mountpoint crossing is very different when stepping up */
                        host_err = nfsd_lookup_parent(rqstp, dparent, &exp, &dentry);
                        if (host_err)
                                goto out_nfserr;
                }
        } else {
                /*
                 * In the nfsd4_open() case, this may be held across
                 * subsequent open and delegation acquisition which may
                 * need to take the child's i_mutex:
                 */
                fh_lock_nested(fhp, I_MUTEX_PARENT);
                dentry = lookup_one_len(name, dparent, len);
                host_err = PTR_ERR(dentry);
                if (IS_ERR(dentry))
                        goto out_nfserr;
                if (nfsd_mountpoint(dentry, exp)) {
                        /*
                         * We don't need the i_mutex after all.  It's
                         * still possible we could open this (regular
                         * files can be mountpoints too), but the
                         * i_mutex is just there to prevent renames of
                         * something that we might be about to delegate,
                         * and a mountpoint won't be renamed:
                         */
                        fh_unlock(fhp);
                        if ((host_err = nfsd_cross_mnt(rqstp, &dentry, &exp))) {
                                dput(dentry);
                                goto out_nfserr;
                        }
                }
        }
        *dentry_ret = dentry;
        *exp_ret = exp;
        return 0;

out_nfserr:
        exp_put(exp);
        return nfserrno(host_err);
}

/*
 * Look up one component of a pathname.
 * N.B. After this call _both_ fhp and resfh need an fh_put
 *
 * If the lookup would cross a mountpoint, and the mounted filesystem
 * is exported to the client with NFSEXP_NOHIDE, then the lookup is
 * accepted as it stands and the mounted directory is
 * returned. Otherwise the covered directory is returned.
 * NOTE: this mountpoint crossing is not supported properly by all
 *   clients and is explicitly disallowed for NFSv3
 *      NeilBrown <neilb@cse.unsw.edu.au>
 */
__be32
nfsd_lookup(struct svc_rqst *rqstp, struct svc_fh *fhp, const char *name,
                                unsigned int len, struct svc_fh *resfh)
{
        struct svc_export       *exp;
        struct dentry           *dentry;
        __be32 err;

        err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_EXEC);
        if (err)
                return err;
        err = nfsd_lookup_dentry(rqstp, fhp, name, len, &exp, &dentry);
        if (err)
                return err;
        err = check_nfsd_access(exp, rqstp);
        if (err)
                goto out;
        /*
         * Note: we compose the file handle now, but as the
         * dentry may be negative, it may need to be updated.
         */
        err = fh_compose(resfh, exp, dentry, fhp);
        if (!err && d_really_is_negative(dentry))
                err = nfserr_noent;
out:
        dput(dentry);
        exp_put(exp);
        return err;
}

/*
 * Commit metadata changes to stable storage.
 */
static int
commit_inode_metadata(struct inode *inode)
{
        const struct export_operations *export_ops = inode->i_sb->s_export_op;

        if (export_ops->commit_metadata)
                return export_ops->commit_metadata(inode);
        return sync_inode_metadata(inode, 1);
}

static int
commit_metadata(struct svc_fh *fhp)
{
        struct inode *inode = d_inode(fhp->fh_dentry);

        if (!EX_ISSYNC(fhp->fh_export))
                return 0;
        return commit_inode_metadata(inode);
}

/*
 * Go over the attributes and take care of the small differences between
 * NFS semantics and what Linux expects.
 */
static void
nfsd_sanitize_attrs(struct inode *inode, struct iattr *iap)
{
        /* sanitize the mode change */
        if (iap->ia_valid & ATTR_MODE) {
                iap->ia_mode &= S_IALLUGO;
                iap->ia_mode |= (inode->i_mode & ~S_IALLUGO);
        }

        /* Revoke setuid/setgid on chown */
        if (!S_ISDIR(inode->i_mode) &&
            ((iap->ia_valid & ATTR_UID) || (iap->ia_valid & ATTR_GID))) {
                iap->ia_valid |= ATTR_KILL_PRIV;
                if (iap->ia_valid & ATTR_MODE) {
                        /* we're setting mode too, just clear the s*id bits */
                        iap->ia_mode &= ~S_ISUID;
                        if (iap->ia_mode & S_IXGRP)
                                iap->ia_mode &= ~S_ISGID;
                } else {
                        /* set ATTR_KILL_* bits and let VFS handle it */
                        iap->ia_valid |= (ATTR_KILL_SUID | ATTR_KILL_SGID);
                }
        }
}

static __be32
nfsd_get_write_access(struct svc_rqst *rqstp, struct svc_fh *fhp,
                struct iattr *iap)
{
        struct inode *inode = d_inode(fhp->fh_dentry);
        int host_err;

        if (iap->ia_size < inode->i_size) {
                __be32 err;

                err = nfsd_permission(rqstp, fhp->fh_export, fhp->fh_dentry,
                                NFSD_MAY_TRUNC | NFSD_MAY_OWNER_OVERRIDE);
                if (err)
                        return err;
        }

        host_err = get_write_access(inode);
        if (host_err)
                goto out_nfserrno;

        host_err = locks_verify_truncate(inode, NULL, iap->ia_size);
        if (host_err)
                goto out_put_write_access;
        return 0;

out_put_write_access:
        put_write_access(inode);
out_nfserrno:
        return nfserrno(host_err);
}

/*
 * Set various file attributes.  After this call fhp needs an fh_put.
 */
__be32
nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap,
             int check_guard, time64_t guardtime)
{
        struct dentry   *dentry;
        struct inode    *inode;
        int             accmode = NFSD_MAY_SATTR;
        umode_t         ftype = 0;
        __be32          err;
        int             host_err;
        bool            get_write_count;
        bool            size_change = (iap->ia_valid & ATTR_SIZE);

        if (iap->ia_valid & ATTR_SIZE) {
                accmode |= NFSD_MAY_WRITE|NFSD_MAY_OWNER_OVERRIDE;
                ftype = S_IFREG;
        }

        /*
         * If utimes(2) and friends are called with times not NULL, we should
         * not set NFSD_MAY_WRITE bit. Otherwise fh_verify->nfsd_permission
         * will return EACCES, when the caller's effective UID does not match
         * the owner of the file, and the caller is not privileged. In this
         * situation, we should return EPERM(notify_change will return this).
         */
        if (iap->ia_valid & (ATTR_ATIME | ATTR_MTIME)) {
                accmode |= NFSD_MAY_OWNER_OVERRIDE;
                if (!(iap->ia_valid & (ATTR_ATIME_SET | ATTR_MTIME_SET)))
                        accmode |= NFSD_MAY_WRITE;
        }

        /* Callers that do fh_verify should do the fh_want_write: */
        get_write_count = !fhp->fh_dentry;

        /* Get inode */
        err = fh_verify(rqstp, fhp, ftype, accmode);
        if (err)
                return err;
        if (get_write_count) {
                host_err = fh_want_write(fhp);
                if (host_err)
                        goto out;
        }

        dentry = fhp->fh_dentry;
        inode = d_inode(dentry);

        /* Ignore any mode updates on symlinks */
        if (S_ISLNK(inode->i_mode))
                iap->ia_valid &= ~ATTR_MODE;

        if (!iap->ia_valid)
                return 0;

        nfsd_sanitize_attrs(inode, iap);

        if (check_guard && guardtime != inode->i_ctime.tv_sec)
                return nfserr_notsync;

        /*
         * The size case is special, it changes the file in addition to the
         * attributes, and file systems don't expect it to be mixed with
         * "random" attribute changes.  We thus split out the size change
         * into a separate call to ->setattr, and do the rest as a separate
         * setattr call.
         */
        if (size_change) {
                err = nfsd_get_write_access(rqstp, fhp, iap);
                if (err)
                        return err;
        }

        fh_lock(fhp);
        if (size_change) {
                /*
                 * RFC5661, Section 18.30.4:
                 *   Changing the size of a file with SETATTR indirectly
                 *   changes the time_modify and change attributes.
                 *
                 * (and similar for the older RFCs)
                 */
                struct iattr size_attr = {
                        .ia_valid       = ATTR_SIZE | ATTR_CTIME | ATTR_MTIME,
                        .ia_size        = iap->ia_size,
                };

                host_err = notify_change(dentry, &size_attr, NULL);
                if (host_err)
                        goto out_unlock;
                iap->ia_valid &= ~ATTR_SIZE;

                /*
                 * Avoid the additional setattr call below if the only other
                 * attribute that the client sends is the mtime, as we update
                 * it as part of the size change above.
                 */
                if ((iap->ia_valid & ~ATTR_MTIME) == 0)
                        goto out_unlock;
        }

        iap->ia_valid |= ATTR_CTIME;
        host_err = notify_change(dentry, iap, NULL);

out_unlock:
        fh_unlock(fhp);
        if (size_change)
                put_write_access(inode);
out:
        if (!host_err)
                host_err = commit_metadata(fhp);
        return nfserrno(host_err);
}

#if defined(CONFIG_NFSD_V4)
/*
 * NFS junction information is stored in an extended attribute.
 */
#define NFSD_JUNCTION_XATTR_NAME        XATTR_TRUSTED_PREFIX "junction.nfs"

/**
 * nfsd4_is_junction - Test if an object could be an NFS junction
 *
 * @dentry: object to test
 *
 * Returns 1 if "dentry" appears to contain NFS junction information.
 * Otherwise 0 is returned.
 */
int nfsd4_is_junction(struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);

        if (inode == NULL)
                return 0;
        if (inode->i_mode & S_IXUGO)
                return 0;
        if (!(inode->i_mode & S_ISVTX))
                return 0;
        if (vfs_getxattr(dentry, NFSD_JUNCTION_XATTR_NAME, NULL, 0) <= 0)
                return 0;
        return 1;
}
#ifdef CONFIG_NFSD_V4_SECURITY_LABEL
__be32 nfsd4_set_nfs4_label(struct svc_rqst *rqstp, struct svc_fh *fhp,
                struct xdr_netobj *label)
{
        __be32 error;
        int host_error;
        struct dentry *dentry;

        error = fh_verify(rqstp, fhp, 0 /* S_IFREG */, NFSD_MAY_SATTR);
        if (error)
                return error;

        dentry = fhp->fh_dentry;

        inode_lock(d_inode(dentry));
        host_error = security_inode_setsecctx(dentry, label->data, label->len);
        inode_unlock(d_inode(dentry));
        return nfserrno(host_error);
}
#else
__be32 nfsd4_set_nfs4_label(struct svc_rqst *rqstp, struct svc_fh *fhp,
                struct xdr_netobj *label)
{
        return nfserr_notsupp;
}
#endif

__be32 nfsd4_clone_file_range(struct nfsd_file *nf_src, u64 src_pos,
                struct nfsd_file *nf_dst, u64 dst_pos, u64 count, bool sync)
{
        struct file *src = nf_src->nf_file;
        struct file *dst = nf_dst->nf_file;
        loff_t cloned;
        __be32 ret = 0;

        down_write(&nf_dst->nf_rwsem);
        cloned = vfs_clone_file_range(src, src_pos, dst, dst_pos, count, 0);
        if (cloned < 0) {
                ret = nfserrno(cloned);
                goto out_err;
        }
        if (count && cloned != count) {
                ret = nfserrno(-EINVAL);
                goto out_err;
        }
        if (sync) {
                loff_t dst_end = count ? dst_pos + count - 1 : LLONG_MAX;
                int status = vfs_fsync_range(dst, dst_pos, dst_end, 0);

                if (!status)
                        status = commit_inode_metadata(file_inode(src));
                if (status < 0) {
                        nfsd_reset_boot_verifier(net_generic(nf_dst->nf_net,
                                                 nfsd_net_id));
                        ret = nfserrno(status);
                }
        }
out_err:
        up_write(&nf_dst->nf_rwsem);
        return ret;
}

ssize_t nfsd_copy_file_range(struct file *src, u64 src_pos, struct file *dst,
                             u64 dst_pos, u64 count)
{

        /*
         * Limit copy to 4MB to prevent indefinitely blocking an nfsd
         * thread and client rpc slot.  The choice of 4MB is somewhat
         * arbitrary.  We might instead base this on r/wsize, or make it
         * tunable, or use a time instead of a byte limit, or implement
         * asynchronous copy.  In theory a client could also recognize a
         * limit like this and pipeline multiple COPY requests.
         */
        count = min_t(u64, count, 1 << 22);
        return vfs_copy_file_range(src, src_pos, dst, dst_pos, count, 0);
}

__be32 nfsd4_vfs_fallocate(struct svc_rqst *rqstp, struct svc_fh *fhp,
                           struct file *file, loff_t offset, loff_t len,
                           int flags)
{
        int error;

        if (!S_ISREG(file_inode(file)->i_mode))
                return nfserr_inval;

        error = vfs_fallocate(file, flags, offset, len);
        if (!error)
                error = commit_metadata(fhp);

        return nfserrno(error);
}
#endif /* defined(CONFIG_NFSD_V4) */

#ifdef CONFIG_NFSD_V3
/*
 * Check server access rights to a file system object
 */
struct accessmap {
        u32             access;
        int             how;
};
static struct accessmap nfs3_regaccess[] = {
    {   NFS3_ACCESS_READ,       NFSD_MAY_READ                   },
    {   NFS3_ACCESS_EXECUTE,    NFSD_MAY_EXEC                   },
    {   NFS3_ACCESS_MODIFY,     NFSD_MAY_WRITE|NFSD_MAY_TRUNC   },
    {   NFS3_ACCESS_EXTEND,     NFSD_MAY_WRITE                  },

#ifdef CONFIG_NFSD_V4
    {   NFS4_ACCESS_XAREAD,     NFSD_MAY_READ                   },
    {   NFS4_ACCESS_XAWRITE,    NFSD_MAY_WRITE                  },
    {   NFS4_ACCESS_XALIST,     NFSD_MAY_READ                   },
#endif

    {   0,                      0                               }
};

static struct accessmap nfs3_diraccess[] = {
    {   NFS3_ACCESS_READ,       NFSD_MAY_READ                   },
    {   NFS3_ACCESS_LOOKUP,     NFSD_MAY_EXEC                   },
    {   NFS3_ACCESS_MODIFY,     NFSD_MAY_EXEC|NFSD_MAY_WRITE|NFSD_MAY_TRUNC},
    {   NFS3_ACCESS_EXTEND,     NFSD_MAY_EXEC|NFSD_MAY_WRITE    },
    {   NFS3_ACCESS_DELETE,     NFSD_MAY_REMOVE                 },

#ifdef CONFIG_NFSD_V4
    {   NFS4_ACCESS_XAREAD,     NFSD_MAY_READ                   },
    {   NFS4_ACCESS_XAWRITE,    NFSD_MAY_WRITE                  },
    {   NFS4_ACCESS_XALIST,     NFSD_MAY_READ                   },
#endif

    {   0,                      0                               }
};

static struct accessmap nfs3_anyaccess[] = {
        /* Some clients - Solaris 2.6 at least, make an access call
         * to the server to check for access for things like /dev/null
         * (which really, the server doesn't care about).  So
         * We provide simple access checking for them, looking
         * mainly at mode bits, and we make sure to ignore read-only
         * filesystem checks
         */
    {   NFS3_ACCESS_READ,       NFSD_MAY_READ                   },
    {   NFS3_ACCESS_EXECUTE,    NFSD_MAY_EXEC                   },
    {   NFS3_ACCESS_MODIFY,     NFSD_MAY_WRITE|NFSD_MAY_LOCAL_ACCESS    },
    {   NFS3_ACCESS_EXTEND,     NFSD_MAY_WRITE|NFSD_MAY_LOCAL_ACCESS    },

    {   0,                      0                               }
};

__be32
nfsd_access(struct svc_rqst *rqstp, struct svc_fh *fhp, u32 *access, u32 *supported)
{
        struct accessmap        *map;
        struct svc_export       *export;
        struct dentry           *dentry;
        u32                     query, result = 0, sresult = 0;
        __be32                  error;

        error = fh_verify(rqstp, fhp, 0, NFSD_MAY_NOP);
        if (error)
                goto out;

        export = fhp->fh_export;
        dentry = fhp->fh_dentry;

        if (d_is_reg(dentry))
                map = nfs3_regaccess;
        else if (d_is_dir(dentry))
                map = nfs3_diraccess;
        else
                map = nfs3_anyaccess;


        query = *access;
        for  (; map->access; map++) {
                if (map->access & query) {
                        __be32 err2;

                        sresult |= map->access;

                        err2 = nfsd_permission(rqstp, export, dentry, map->how);
                        switch (err2) {
                        case nfs_ok:
                                result |= map->access;
                                break;
                                
                        /* the following error codes just mean the access was not allowed,
                         * rather than an error occurred */
                        case nfserr_rofs:
                        case nfserr_acces:
                        case nfserr_perm:
                                /* simply don't "or" in the access bit. */
                                break;
                        default:
                                error = err2;
                                goto out;
                        }
                }
        }
        *access = result;
        if (supported)
                *supported = sresult;

 out:
        return error;
}
#endif /* CONFIG_NFSD_V3 */

int nfsd_open_break_lease(struct inode *inode, int access)
{
        unsigned int mode;

        if (access & NFSD_MAY_NOT_BREAK_LEASE)
                return 0;
        mode = (access & NFSD_MAY_WRITE) ? O_WRONLY : O_RDONLY;
        return break_lease(inode, mode | O_NONBLOCK);
}

/*
 * Open an existing file or directory.
 * The may_flags argument indicates the type of open (read/write/lock)
 * and additional flags.
 * N.B. After this call fhp needs an fh_put
 */
static __be32
__nfsd_open(struct svc_rqst *rqstp, struct svc_fh *fhp, umode_t type,
                        int may_flags, struct file **filp)
{
        struct path     path;
        struct inode    *inode;
        struct file     *file;
        int             flags = O_RDONLY|O_LARGEFILE;
        __be32          err;
        int             host_err = 0;

        path.mnt = fhp->fh_export->ex_path.mnt;
        path.dentry = fhp->fh_dentry;
        inode = d_inode(path.dentry);

        /* Disallow write access to files with the append-only bit set
         * or any access when mandatory locking enabled
         */
        err = nfserr_perm;
        if (IS_APPEND(inode) && (may_flags & NFSD_MAY_WRITE))
                goto out;
        /*
         * We must ignore files (but only files) which might have mandatory
         * locks on them because there is no way to know if the accesser has
         * the lock.
         */
        if (S_ISREG((inode)->i_mode) && mandatory_lock(inode))
                goto out;

        if (!inode->i_fop)
                goto out;

        host_err = nfsd_open_break_lease(inode, may_flags);
        if (host_err) /* NOMEM or WOULDBLOCK */
                goto out_nfserr;

        if (may_flags & NFSD_MAY_WRITE) {
                if (may_flags & NFSD_MAY_READ)
                        flags = O_RDWR|O_LARGEFILE;
                else
                        flags = O_WRONLY|O_LARGEFILE;
        }

        file = dentry_open(&path, flags, current_cred());
        if (IS_ERR(file)) {
                host_err = PTR_ERR(file);
                goto out_nfserr;
        }

        host_err = ima_file_check(file, may_flags);
        if (host_err) {
                fput(file);
                goto out_nfserr;
        }

        if (may_flags & NFSD_MAY_64BIT_COOKIE)
                file->f_mode |= FMODE_64BITHASH;
        else
                file->f_mode |= FMODE_32BITHASH;

        *filp = file;
out_nfserr:
        err = nfserrno(host_err);
out:
        return err;
}

__be32
nfsd_open(struct svc_rqst *rqstp, struct svc_fh *fhp, umode_t type,
                int may_flags, struct file **filp)
{
        __be32 err;

        validate_process_creds();
        /*
         * If we get here, then the client has already done an "open",
         * and (hopefully) checked permission - so allow OWNER_OVERRIDE
         * in case a chmod has now revoked permission.
         *
         * Arguably we should also allow the owner override for
         * directories, but we never have and it doesn't seem to have
         * caused anyone a problem.  If we were to change this, note
         * also that our filldir callbacks would need a variant of
         * lookup_one_len that doesn't check permissions.
         */
        if (type == S_IFREG)
                may_flags |= NFSD_MAY_OWNER_OVERRIDE;
        err = fh_verify(rqstp, fhp, type, may_flags);
        if (!err)
                err = __nfsd_open(rqstp, fhp, type, may_flags, filp);
        validate_process_creds();
        return err;
}

__be32
nfsd_open_verified(struct svc_rqst *rqstp, struct svc_fh *fhp, umode_t type,
                int may_flags, struct file **filp)
{
        __be32 err;

        validate_process_creds();
        err = __nfsd_open(rqstp, fhp, type, may_flags, filp);
        validate_process_creds();
        return err;
}

/*
 * Grab and keep cached pages associated with a file in the svc_rqst
 * so that they can be passed to the network sendmsg/sendpage routines
 * directly. They will be released after the sending has completed.
 */
static int
nfsd_splice_actor(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
                  struct splice_desc *sd)
{
        struct svc_rqst *rqstp = sd->u.data;
        struct page **pp = rqstp->rq_next_page;
        struct page *page = buf->page;
        size_t size;

        size = sd->len;

        if (rqstp->rq_res.page_len == 0) {
                get_page(page);
                put_page(*rqstp->rq_next_page);
                *(rqstp->rq_next_page++) = page;
                rqstp->rq_res.page_base = buf->offset;
                rqstp->rq_res.page_len = size;
        } else if (page != pp[-1]) {
                get_page(page);
                if (*rqstp->rq_next_page)
                        put_page(*rqstp->rq_next_page);
                *(rqstp->rq_next_page++) = page;
                rqstp->rq_res.page_len += size;
        } else
                rqstp->rq_res.page_len += size;

        return size;
}

static int nfsd_direct_splice_actor(struct pipe_inode_info *pipe,
                                    struct splice_desc *sd)
{
        return __splice_from_pipe(pipe, sd, nfsd_splice_actor);
}

static u32 nfsd_eof_on_read(struct file *file, loff_t offset, ssize_t len,
                size_t expected)
{
        if (expected != 0 && len == 0)
                return 1;
        if (offset+len >= i_size_read(file_inode(file)))
                return 1;
        return 0;
}

static __be32 nfsd_finish_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
                               struct file *file, loff_t offset,
                               unsigned long *count, u32 *eof, ssize_t host_err)
{
        if (host_err >= 0) {
                nfsdstats.io_read += host_err;
                *eof = nfsd_eof_on_read(file, offset, host_err, *count);
                *count = host_err;
                fsnotify_access(file);
                trace_nfsd_read_io_done(rqstp, fhp, offset, *count);
                return 0;
        } else {
                trace_nfsd_read_err(rqstp, fhp, offset, host_err);
                return nfserrno(host_err);
        }
}

__be32 nfsd_splice_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
                        struct file *file, loff_t offset, unsigned long *count,
                        u32 *eof)
{
        struct splice_desc sd = {
                .len            = 0,
                .total_len      = *count,
                .pos            = offset,
                .u.data         = rqstp,
        };
        ssize_t host_err;

        trace_nfsd_read_splice(rqstp, fhp, offset, *count);
        rqstp->rq_next_page = rqstp->rq_respages + 1;
        host_err = splice_direct_to_actor(file, &sd, nfsd_direct_splice_actor);
        return nfsd_finish_read(rqstp, fhp, file, offset, count, eof, host_err);
}

__be32 nfsd_readv(struct svc_rqst *rqstp, struct svc_fh *fhp,
                  struct file *file, loff_t offset,
                  struct kvec *vec, int vlen, unsigned long *count,
                  u32 *eof)
{
        struct iov_iter iter;
        loff_t ppos = offset;
        ssize_t host_err;

        trace_nfsd_read_vector(rqstp, fhp, offset, *count);
        iov_iter_kvec(&iter, READ, vec, vlen, *count);
        host_err = vfs_iter_read(file, &iter, &ppos, 0);
        return nfsd_finish_read(rqstp, fhp, file, offset, count, eof, host_err);
}

/*
 * Gathered writes: If another process is currently writing to the file,
 * there's a high chance this is another nfsd (triggered by a bulk write
 * from a client's biod). Rather than syncing the file with each write
 * request, we sleep for 10 msec.
 *
 * I don't know if this roughly approximates C. Juszak's idea of
 * gathered writes, but it's a nice and simple solution (IMHO), and it
 * seems to work:-)
 *
 * Note: we do this only in the NFSv2 case, since v3 and higher have a
 * better tool (separate unstable writes and commits) for solving this
 * problem.
 */
static int wait_for_concurrent_writes(struct file *file)
{
        struct inode *inode = file_inode(file);
        static ino_t last_ino;
        static dev_t last_dev;
        int err = 0;

        if (atomic_read(&inode->i_writecount) > 1
            || (last_ino == inode->i_ino && last_dev == inode->i_sb->s_dev)) {
                dprintk("nfsd: write defer %d\n", task_pid_nr(current));
                msleep(10);
                dprintk("nfsd: write resume %d\n", task_pid_nr(current));
        }

        if (inode->i_state & I_DIRTY) {
                dprintk("nfsd: write sync %d\n", task_pid_nr(current));
                err = vfs_fsync(file, 0);
        }
        last_ino = inode->i_ino;
        last_dev = inode->i_sb->s_dev;
        return err;
}

__be32
nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf,
                                loff_t offset, struct kvec *vec, int vlen,
                                unsigned long *cnt, int stable,
                                __be32 *verf)
{
        struct file             *file = nf->nf_file;
        struct super_block      *sb = file_inode(file)->i_sb;
        struct svc_export       *exp;
        struct iov_iter         iter;
        __be32                  nfserr;
        int                     host_err;
        int                     use_wgather;
        loff_t                  pos = offset;
        unsigned long           exp_op_flags = 0;
        unsigned int            pflags = current->flags;
        rwf_t                   flags = 0;
        bool                    restore_flags = false;

        trace_nfsd_write_opened(rqstp, fhp, offset, *cnt);

        if (sb->s_export_op)
                exp_op_flags = sb->s_export_op->flags;

        if (test_bit(RQ_LOCAL, &rqstp->rq_flags) &&
            !(exp_op_flags & EXPORT_OP_REMOTE_FS)) {
                /*
                 * We want throttling in balance_dirty_pages()
                 * and shrink_inactive_list() to only consider
                 * the backingdev we are writing to, so that nfs to
                 * localhost doesn't cause nfsd to lock up due to all
                 * the client's dirty pages or its congested queue.
                 */
                current->flags |= PF_LOCAL_THROTTLE;
                restore_flags = true;
        }

        exp = fhp->fh_export;
        use_wgather = (rqstp->rq_vers == 2) && EX_WGATHER(exp);

        if (!EX_ISSYNC(exp))
                stable = NFS_UNSTABLE;

        if (stable && !use_wgather)
                flags |= RWF_SYNC;

        iov_iter_kvec(&iter, WRITE, vec, vlen, *cnt);
        if (flags & RWF_SYNC) {
                down_write(&nf->nf_rwsem);
                host_err = vfs_iter_write(file, &iter, &pos, flags);
                if (host_err < 0)
                        nfsd_reset_boot_verifier(net_generic(SVC_NET(rqstp),
                                                 nfsd_net_id));
                up_write(&nf->nf_rwsem);
        } else {
                down_read(&nf->nf_rwsem);
                if (verf)
                        nfsd_copy_boot_verifier(verf,
                                        net_generic(SVC_NET(rqstp),
                                        nfsd_net_id));
                host_err = vfs_iter_write(file, &iter, &pos, flags);
                up_read(&nf->nf_rwsem);
        }
        if (host_err < 0) {
                nfsd_reset_boot_verifier(net_generic(SVC_NET(rqstp),
                                         nfsd_net_id));
                goto out_nfserr;
        }
        *cnt = host_err;
        nfsdstats.io_write += *cnt;
        fsnotify_modify(file);

        if (stable && use_wgather) {
                host_err = wait_for_concurrent_writes(file);
                if (host_err < 0)
                        nfsd_reset_boot_verifier(net_generic(SVC_NET(rqstp),
                                                 nfsd_net_id));
        }

out_nfserr:
        if (host_err >= 0) {
                trace_nfsd_write_io_done(rqstp, fhp, offset, *cnt);
                nfserr = nfs_ok;
        } else {
                trace_nfsd_write_err(rqstp, fhp, offset, host_err);
                nfserr = nfserrno(host_err);
        }
        if (restore_flags)
                current_restore_flags(pflags, PF_LOCAL_THROTTLE);
        return nfserr;
}

/*
 * Read data from a file. count must contain the requested read count
 * on entry. On return, *count contains the number of bytes actually read.
 * N.B. After this call fhp needs an fh_put
 */
__be32 nfsd_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
        loff_t offset, struct kvec *vec, int vlen, unsigned long *count,
        u32 *eof)
{
        struct nfsd_file        *nf;
        struct file *file;
        __be32 err;

        trace_nfsd_read_start(rqstp, fhp, offset, *count);
        err = nfsd_file_acquire(rqstp, fhp, NFSD_MAY_READ, &nf);
        if (err)
                return err;

        file = nf->nf_file;
        if (file->f_op->splice_read && test_bit(RQ_SPLICE_OK, &rqstp->rq_flags))
                err = nfsd_splice_read(rqstp, fhp, file, offset, count, eof);
        else
                err = nfsd_readv(rqstp, fhp, file, offset, vec, vlen, count, eof);

        nfsd_file_put(nf);

        trace_nfsd_read_done(rqstp, fhp, offset, *count);

        return err;
}

/*
 * Write data to a file.
 * The stable flag requests synchronous writes.
 * N.B. After this call fhp needs an fh_put
 */
__be32
nfsd_write(struct svc_rqst *rqstp, struct svc_fh *fhp, loff_t offset,
           struct kvec *vec, int vlen, unsigned long *cnt, int stable,
           __be32 *verf)
{
        struct nfsd_file *nf;
        __be32 err;

        trace_nfsd_write_start(rqstp, fhp, offset, *cnt);

        err = nfsd_file_acquire(rqstp, fhp, NFSD_MAY_WRITE, &nf);
        if (err)
                goto out;

        err = nfsd_vfs_write(rqstp, fhp, nf, offset, vec,
                        vlen, cnt, stable, verf);
        nfsd_file_put(nf);
out:
        trace_nfsd_write_done(rqstp, fhp, offset, *cnt);
        return err;
}

#ifdef CONFIG_NFSD_V3
/*
 * Commit all pending writes to stable storage.
 *
 * Note: we only guarantee that data that lies within the range specified
 * by the 'offset' and 'count' parameters will be synced.
 *
 * Unfortunately we cannot lock the file to make sure we return full WCC
 * data to the client, as locking happens lower down in the filesystem.
 */
__be32
nfsd_commit(struct svc_rqst *rqstp, struct svc_fh *fhp,
               loff_t offset, unsigned long count, __be32 *verf)
{
        struct nfsd_file        *nf;
        loff_t                  end = LLONG_MAX;
        __be32                  err = nfserr_inval;

        if (offset < 0)
                goto out;
        if (count != 0) {
                end = offset + (loff_t)count - 1;
                if (end < offset)
                        goto out;
        }

        err = nfsd_file_acquire(rqstp, fhp,
                        NFSD_MAY_WRITE|NFSD_MAY_NOT_BREAK_LEASE, &nf);
        if (err)
                goto out;
        if (EX_ISSYNC(fhp->fh_export)) {
                int err2;

                down_write(&nf->nf_rwsem);
                err2 = vfs_fsync_range(nf->nf_file, offset, end, 0);
                switch (err2) {
                case 0:
                        nfsd_copy_boot_verifier(verf, net_generic(nf->nf_net,
                                                nfsd_net_id));
                        break;
                case -EINVAL:
                        err = nfserr_notsupp;
                        break;
                default:
                        err = nfserrno(err2);
                        nfsd_reset_boot_verifier(net_generic(nf->nf_net,
                                                 nfsd_net_id));
                }
                up_write(&nf->nf_rwsem);
        } else
                nfsd_copy_boot_verifier(verf, net_generic(nf->nf_net,
                                        nfsd_net_id));

        nfsd_file_put(nf);
out:
        return err;
}
#endif /* CONFIG_NFSD_V3 */

static __be32
nfsd_create_setattr(struct svc_rqst *rqstp, struct svc_fh *resfhp,
                        struct iattr *iap)
{
        /*
         * Mode has already been set earlier in create:
         */
        iap->ia_valid &= ~ATTR_MODE;
        /*
         * Setting uid/gid works only for root.  Irix appears to
         * send along the gid on create when it tries to implement
         * setgid directories via NFS:
         */
        if (!uid_eq(current_fsuid(), GLOBAL_ROOT_UID))
                iap->ia_valid &= ~(ATTR_UID|ATTR_GID);
        if (iap->ia_valid)
                return nfsd_setattr(rqstp, resfhp, iap, 0, (time64_t)0);
        /* Callers expect file metadata to be committed here */
        return nfserrno(commit_metadata(resfhp));
}

/* HPUX client sometimes creates a file in mode 000, and sets size to 0.
 * setting size to 0 may fail for some specific file systems by the permission
 * checking which requires WRITE permission but the mode is 000.
 * we ignore the resizing(to 0) on the just new created file, since the size is
 * 0 after file created.
 *
 * call this only after vfs_create() is called.
 * */
static void
nfsd_check_ignore_resizing(struct iattr *iap)
{
        if ((iap->ia_valid & ATTR_SIZE) && (iap->ia_size == 0))
                iap->ia_valid &= ~ATTR_SIZE;
}

/* The parent directory should already be locked: */
__be32
nfsd_create_locked(struct svc_rqst *rqstp, struct svc_fh *fhp,
                char *fname, int flen, struct iattr *iap,
                int type, dev_t rdev, struct svc_fh *resfhp)
{
        struct dentry   *dentry, *dchild;
        struct inode    *dirp;
        __be32          err;
        __be32          err2;
        int             host_err;

        dentry = fhp->fh_dentry;
        dirp = d_inode(dentry);

        dchild = dget(resfhp->fh_dentry);
        if (!fhp->fh_locked) {
                WARN_ONCE(1, "nfsd_create: parent %pd2 not locked!\n",
                                dentry);
                err = nfserr_io;
                goto out;
        }

        err = nfsd_permission(rqstp, fhp->fh_export, dentry, NFSD_MAY_CREATE);
        if (err)
                goto out;

        if (!(iap->ia_valid & ATTR_MODE))
                iap->ia_mode = 0;
        iap->ia_mode = (iap->ia_mode & S_IALLUGO) | type;

        if (!IS_POSIXACL(dirp))
                iap->ia_mode &= ~current_umask();

        err = 0;
        host_err = 0;
        switch (type) {
        case S_IFREG:
                host_err = vfs_create(dirp, dchild, iap->ia_mode, true);
                if (!host_err)
                        nfsd_check_ignore_resizing(iap);
                break;
        case S_IFDIR:
                host_err = vfs_mkdir(dirp, dchild, iap->ia_mode);
                if (!host_err && unlikely(d_unhashed(dchild))) {
                        struct dentry *d;
                        d = lookup_one_len(dchild->d_name.name,
                                           dchild->d_parent,
                                           dchild->d_name.len);
                        if (IS_ERR(d)) {
                                host_err = PTR_ERR(d);
                                break;
                        }
                        if (unlikely(d_is_negative(d))) {
                                dput(d);
                                err = nfserr_serverfault;
                                goto out;
                        }
                        dput(resfhp->fh_dentry);
                        resfhp->fh_dentry = dget(d);
                        err = fh_update(resfhp);
                        dput(dchild);
                        dchild = d;
                        if (err)
                                goto out;
                }
                break;
        case S_IFCHR:
        case S_IFBLK:
        case S_IFIFO:
        case S_IFSOCK:
                host_err = vfs_mknod(dirp, dchild, iap->ia_mode, rdev);
                break;
        default:
                printk(KERN_WARNING "nfsd: bad file type %o in nfsd_create\n",
                       type);
                host_err = -EINVAL;
        }
        if (host_err < 0)
                goto out_nfserr;

        err = nfsd_create_setattr(rqstp, resfhp, iap);

        /*
         * nfsd_create_setattr already committed the child.  Transactional
         * filesystems had a chance to commit changes for both parent and
         * child simultaneously making the following commit_metadata a
         * noop.
         */
        err2 = nfserrno(commit_metadata(fhp));
        if (err2)
                err = err2;
        /*
         * Update the file handle to get the new inode info.
         */
        if (!err)
                err = fh_update(resfhp);
out:
        dput(dchild);
        return err;

out_nfserr:
        err = nfserrno(host_err);
        goto out;
}

/*
 * Create a filesystem object (regular, directory, special).
 * Note that the parent directory is left locked.
 *
 * N.B. Every call to nfsd_create needs an fh_put for _both_ fhp and resfhp
 */
__be32
nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
                char *fname, int flen, struct iattr *iap,
                int type, dev_t rdev, struct svc_fh *resfhp)
{
        struct dentry   *dentry, *dchild = NULL;
        __be32          err;
        int             host_err;

        if (isdotent(fname, flen))
                return nfserr_exist;

        err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_NOP);
        if (err)
                return err;

        dentry = fhp->fh_dentry;

        host_err = fh_want_write(fhp);
        if (host_err)
                return nfserrno(host_err);

        fh_lock_nested(fhp, I_MUTEX_PARENT);
        dchild = lookup_one_len(fname, dentry, flen);
        host_err = PTR_ERR(dchild);
        if (IS_ERR(dchild))
                return nfserrno(host_err);
        err = fh_compose(resfhp, fhp->fh_export, dchild, fhp);
        /*
         * We unconditionally drop our ref to dchild as fh_compose will have
         * already grabbed its own ref for it.
         */
        dput(dchild);
        if (err)
                return err;
        return nfsd_create_locked(rqstp, fhp, fname, flen, iap, type,
                                        rdev, resfhp);
}

#ifdef CONFIG_NFSD_V3

/*
 * NFSv3 and NFSv4 version of nfsd_create
 */
__be32
do_nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
                char *fname, int flen, struct iattr *iap,
                struct svc_fh *resfhp, int createmode, u32 *verifier,
                bool *truncp, bool *created)
{
        struct dentry   *dentry, *dchild = NULL;
        struct inode    *dirp;
        __be32          err;
        int             host_err;
        __u32           v_mtime=0, v_atime=0;

        err = nfserr_perm;
        if (!flen)
                goto out;
        err = nfserr_exist;
        if (isdotent(fname, flen))
                goto out;
        if (!(iap->ia_valid & ATTR_MODE))
                iap->ia_mode = 0;
        err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_EXEC);
        if (err)
                goto out;

        dentry = fhp->fh_dentry;
        dirp = d_inode(dentry);

        host_err = fh_want_write(fhp);
        if (host_err)
                goto out_nfserr;

        fh_lock_nested(fhp, I_MUTEX_PARENT);

        /*
         * Compose the response file handle.
         */
        dchild = lookup_one_len(fname, dentry, flen);
        host_err = PTR_ERR(dchild);
        if (IS_ERR(dchild))
                goto out_nfserr;

        /* If file doesn't exist, check for permissions to create one */
        if (d_really_is_negative(dchild)) {
                err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_CREATE);
                if (err)
                        goto out;
        }

        err = fh_compose(resfhp, fhp->fh_export, dchild, fhp);
        if (err)
                goto out;

        if (nfsd_create_is_exclusive(createmode)) {
                /* solaris7 gets confused (bugid 4218508) if these have
                 * the high bit set, so just clear the high bits. If this is
                 * ever changed to use different attrs for storing the
                 * verifier, then do_open_lookup() will also need to be fixed
                 * accordingly.
                 */
                v_mtime = verifier[0]&0x7fffffff;
                v_atime = verifier[1]&0x7fffffff;
        }
        
        if (d_really_is_positive(dchild)) {
                err = 0;

                switch (createmode) {
                case NFS3_CREATE_UNCHECKED:
                        if (! d_is_reg(dchild))
                                goto out;
                        else if (truncp) {
                                /* in nfsv4, we need to treat this case a little
                                 * differently.  we don't want to truncate the
                                 * file now; this would be wrong if the OPEN
                                 * fails for some other reason.  furthermore,
                                 * if the size is nonzero, we should ignore it
                                 * according to spec!
                                 */
                                *truncp = (iap->ia_valid & ATTR_SIZE) && !iap->ia_size;
                        }
                        else {
                                iap->ia_valid &= ATTR_SIZE;
                                goto set_attr;
                        }
                        break;
                case NFS3_CREATE_EXCLUSIVE:
                        if (   d_inode(dchild)->i_mtime.tv_sec == v_mtime
                            && d_inode(dchild)->i_atime.tv_sec == v_atime
                            && d_inode(dchild)->i_size  == 0 ) {
                                if (created)
                                        *created = true;
                                break;
                        }
                        fallthrough;
                case NFS4_CREATE_EXCLUSIVE4_1:
                        if (   d_inode(dchild)->i_mtime.tv_sec == v_mtime
                            && d_inode(dchild)->i_atime.tv_sec == v_atime
                            && d_inode(dchild)->i_size  == 0 ) {
                                if (created)
                                        *created = true;
                                goto set_attr;
                        }
                        fallthrough;
                case NFS3_CREATE_GUARDED:
                        err = nfserr_exist;
                }
                fh_drop_write(fhp);
                goto out;
        }

        if (!IS_POSIXACL(dirp))
                iap->ia_mode &= ~current_umask();

        host_err = vfs_create(dirp, dchild, iap->ia_mode, true);
        if (host_err < 0) {
                fh_drop_write(fhp);
                goto out_nfserr;
        }
        if (created)
                *created = true;

        nfsd_check_ignore_resizing(iap);

        if (nfsd_create_is_exclusive(createmode)) {
                /* Cram the verifier into atime/mtime */
                iap->ia_valid = ATTR_MTIME|ATTR_ATIME
                        | ATTR_MTIME_SET|ATTR_ATIME_SET;
                /* XXX someone who knows this better please fix it for nsec */ 
                iap->ia_mtime.tv_sec = v_mtime;
                iap->ia_atime.tv_sec = v_atime;
                iap->ia_mtime.tv_nsec = 0;
                iap->ia_atime.tv_nsec = 0;
        }

 set_attr:
        err = nfsd_create_setattr(rqstp, resfhp, iap);

        /*
         * nfsd_create_setattr already committed the child
         * (and possibly also the parent).
         */
        if (!err)
                err = nfserrno(commit_metadata(fhp));

        /*
         * Update the filehandle to get the new inode info.
         */
        if (!err)
                err = fh_update(resfhp);

 out:
        fh_unlock(fhp);
        if (dchild && !IS_ERR(dchild))
                dput(dchild);
        fh_drop_write(fhp);
        return err;
 
 out_nfserr:
        err = nfserrno(host_err);
        goto out;
}
#endif /* CONFIG_NFSD_V3 */

/*
 * Read a symlink. On entry, *lenp must contain the maximum path length that
 * fits into the buffer. On return, it contains the true length.
 * N.B. After this call fhp needs an fh_put
 */
__be32
nfsd_readlink(struct svc_rqst *rqstp, struct svc_fh *fhp, char *buf, int *lenp)
{
        __be32          err;
        const char *link;
        struct path path;
        DEFINE_DELAYED_CALL(done);
        int len;

        err = fh_verify(rqstp, fhp, S_IFLNK, NFSD_MAY_NOP);
        if (unlikely(err))
                return err;

        path.mnt = fhp->fh_export->ex_path.mnt;
        path.dentry = fhp->fh_dentry;

        if (unlikely(!d_is_symlink(path.dentry)))
                return nfserr_inval;

        touch_atime(&path);

        link = vfs_get_link(path.dentry, &done);
        if (IS_ERR(link))
                return nfserrno(PTR_ERR(link));

        len = strlen(link);
        if (len < *lenp)
                *lenp = len;
        memcpy(buf, link, *lenp);
        do_delayed_call(&done);
        return 0;
}

/*
 * Create a symlink and look up its inode
 * N.B. After this call _both_ fhp and resfhp need an fh_put
 */
__be32
nfsd_symlink(struct svc_rqst *rqstp, struct svc_fh *fhp,
                                char *fname, int flen,
                                char *path,
                                struct svc_fh *resfhp)
{
        struct dentry   *dentry, *dnew;
        __be32          err, cerr;
        int             host_err;

        err = nfserr_noent;
        if (!flen || path[0] == '\0')
                goto out;
        err = nfserr_exist;
        if (isdotent(fname, flen))
                goto out;

        err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_CREATE);
        if (err)
                goto out;

        host_err = fh_want_write(fhp);
        if (host_err)
                goto out_nfserr;

        fh_lock(fhp);
        dentry = fhp->fh_dentry;
        dnew = lookup_one_len(fname, dentry, flen);
        host_err = PTR_ERR(dnew);
        if (IS_ERR(dnew))
                goto out_nfserr;

        host_err = vfs_symlink(d_inode(dentry), dnew, path);
        err = nfserrno(host_err);
        if (!err)
                err = nfserrno(commit_metadata(fhp));
        fh_unlock(fhp);

        fh_drop_write(fhp);

        cerr = fh_compose(resfhp, fhp->fh_export, dnew, fhp);
        dput(dnew);
        if (err==0) err = cerr;
out:
        return err;

out_nfserr:
        err = nfserrno(host_err);
        goto out;
}

/*
 * Create a hardlink
 * N.B. After this call _both_ ffhp and tfhp need an fh_put
 */
__be32
nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
                                char *name, int len, struct svc_fh *tfhp)
{
        struct dentry   *ddir, *dnew, *dold;
        struct inode    *dirp;
        __be32          err;
        int             host_err;

        err = fh_verify(rqstp, ffhp, S_IFDIR, NFSD_MAY_CREATE);
        if (err)
                goto out;
        err = fh_verify(rqstp, tfhp, 0, NFSD_MAY_NOP);
        if (err)
                goto out;
        err = nfserr_isdir;
        if (d_is_dir(tfhp->fh_dentry))
                goto out;
        err = nfserr_perm;
        if (!len)
                goto out;
        err = nfserr_exist;
        if (isdotent(name, len))
                goto out;

        host_err = fh_want_write(tfhp);
        if (host_err) {
                err = nfserrno(host_err);
                goto out;
        }

        fh_lock_nested(ffhp, I_MUTEX_PARENT);
        ddir = ffhp->fh_dentry;
        dirp = d_inode(ddir);

        dnew = lookup_one_len(name, ddir, len);
        host_err = PTR_ERR(dnew);
        if (IS_ERR(dnew))
                goto out_nfserr;

        dold = tfhp->fh_dentry;

        err = nfserr_noent;
        if (d_really_is_negative(dold))
                goto out_dput;
        host_err = vfs_link(dold, dirp, dnew, NULL);
        if (!host_err) {
                err = nfserrno(commit_metadata(ffhp));
                if (!err)
                        err = nfserrno(commit_metadata(tfhp));
        } else {
                if (host_err == -EXDEV && rqstp->rq_vers == 2)
                        err = nfserr_acces;
                else
                        err = nfserrno(host_err);
        }
out_dput:
        dput(dnew);
out_unlock:
        fh_unlock(ffhp);
        fh_drop_write(tfhp);
out:
        return err;

out_nfserr:
        err = nfserrno(host_err);
        goto out_unlock;
}

static void
nfsd_close_cached_files(struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);

        if (inode && S_ISREG(inode->i_mode))
                nfsd_file_close_inode_sync(inode);
}

static bool
nfsd_has_cached_files(struct dentry *dentry)
{
        bool            ret = false;
        struct inode *inode = d_inode(dentry);

        if (inode && S_ISREG(inode->i_mode))
                ret = nfsd_file_is_cached(inode);
        return ret;
}

/*
 * Rename a file
 * N.B. After this call _both_ ffhp and tfhp need an fh_put
 */
__be32
nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
                            struct svc_fh *tfhp, char *tname, int tlen)
{
        struct dentry   *fdentry, *tdentry, *odentry, *ndentry, *trap;
        struct inode    *fdir, *tdir;
        __be32          err;
        int             host_err;
        bool            close_cached = false;

        err = fh_verify(rqstp, ffhp, S_IFDIR, NFSD_MAY_REMOVE);
        if (err)
                goto out;
        err = fh_verify(rqstp, tfhp, S_IFDIR, NFSD_MAY_CREATE);
        if (err)
                goto out;

        fdentry = ffhp->fh_dentry;
        fdir = d_inode(fdentry);

        tdentry = tfhp->fh_dentry;
        tdir = d_inode(tdentry);

        err = nfserr_perm;
        if (!flen || isdotent(fname, flen) || !tlen || isdotent(tname, tlen))
                goto out;

retry:
        host_err = fh_want_write(ffhp);
        if (host_err) {
                err = nfserrno(host_err);
                goto out;
        }

        /* cannot use fh_lock as we need deadlock protective ordering
         * so do it by hand */
        trap = lock_rename(tdentry, fdentry);
        ffhp->fh_locked = tfhp->fh_locked = true;
        fill_pre_wcc(ffhp);
        fill_pre_wcc(tfhp);

        odentry = lookup_one_len(fname, fdentry, flen);
        host_err = PTR_ERR(odentry);
        if (IS_ERR(odentry))
                goto out_nfserr;

        host_err = -ENOENT;
        if (d_really_is_negative(odentry))
                goto out_dput_old;
        host_err = -EINVAL;
        if (odentry == trap)
                goto out_dput_old;

        ndentry = lookup_one_len(tname, tdentry, tlen);
        host_err = PTR_ERR(ndentry);
        if (IS_ERR(ndentry))
                goto out_dput_old;
        host_err = -ENOTEMPTY;
        if (ndentry == trap)
                goto out_dput_new;

        host_err = -EXDEV;
        if (ffhp->fh_export->ex_path.mnt != tfhp->fh_export->ex_path.mnt)
                goto out_dput_new;
        if (ffhp->fh_export->ex_path.dentry != tfhp->fh_export->ex_path.dentry)
                goto out_dput_new;

        if ((ndentry->d_sb->s_export_op->flags & EXPORT_OP_CLOSE_BEFORE_UNLINK) &&
            nfsd_has_cached_files(ndentry)) {
                close_cached = true;
                goto out_dput_old;
        } else {
                host_err = vfs_rename(fdir, odentry, tdir, ndentry, NULL, 0);
                if (!host_err) {
                        host_err = commit_metadata(tfhp);
                        if (!host_err)
                                host_err = commit_metadata(ffhp);
                }
        }
 out_dput_new:
        dput(ndentry);
 out_dput_old:
        dput(odentry);
 out_nfserr:
        err = nfserrno(host_err);
        /*
         * We cannot rely on fh_unlock on the two filehandles,
         * as that would do the wrong thing if the two directories
         * were the same, so again we do it by hand.
         */
        if (!close_cached) {
                fill_post_wcc(ffhp);
                fill_post_wcc(tfhp);
        }
        unlock_rename(tdentry, fdentry);
        ffhp->fh_locked = tfhp->fh_locked = false;
        fh_drop_write(ffhp);

        /*
         * If the target dentry has cached open files, then we need to try to
         * close them prior to doing the rename. Flushing delayed fput
         * shouldn't be done with locks held however, so we delay it until this
         * point and then reattempt the whole shebang.
         */
        if (close_cached) {
                close_cached = false;
                nfsd_close_cached_files(ndentry);
                dput(ndentry);
                goto retry;
        }
out:
        return err;
}

/*
 * Unlink a file or directory
 * N.B. After this call fhp needs an fh_put
 */
__be32
nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
                                char *fname, int flen)
{
        struct dentry   *dentry, *rdentry;
        struct inode    *dirp;
        __be32          err;
        int             host_err;

        err = nfserr_acces;
        if (!flen || isdotent(fname, flen))
                goto out;
        err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_REMOVE);
        if (err)
                goto out;

        host_err = fh_want_write(fhp);
        if (host_err)
                goto out_nfserr;

        fh_lock_nested(fhp, I_MUTEX_PARENT);
        dentry = fhp->fh_dentry;
        dirp = d_inode(dentry);

        rdentry = lookup_one_len(fname, dentry, flen);
        host_err = PTR_ERR(rdentry);
        if (IS_ERR(rdentry))
                goto out_drop_write;

        if (d_really_is_negative(rdentry)) {
                dput(rdentry);
                host_err = -ENOENT;
                goto out_drop_write;
        }

        if (!type)
                type = d_inode(rdentry)->i_mode & S_IFMT;

        if (type != S_IFDIR) {
                if (rdentry->d_sb->s_export_op->flags & EXPORT_OP_CLOSE_BEFORE_UNLINK)
                        nfsd_close_cached_files(rdentry);
                host_err = vfs_unlink(dirp, rdentry, NULL);
        } else {
                host_err = vfs_rmdir(dirp, rdentry);
        }

        if (!host_err)
                host_err = commit_metadata(fhp);
        dput(rdentry);

out_drop_write:
        fh_drop_write(fhp);
out_nfserr:
        if (host_err == -EBUSY) {
                /* name is mounted-on. There is no perfect
                 * error status.
                 */
                if (nfsd_v4client(rqstp))
                        err = nfserr_file_open;
                else
                        err = nfserr_acces;
        } else {
                err = nfserrno(host_err);
        }
out:
        return err;
}

/*
 * We do this buffering because we must not call back into the file
 * system's ->lookup() method from the filldir callback. That may well
 * deadlock a number of file systems.
 *
 * This is based heavily on the implementation of same in XFS.
 */
struct buffered_dirent {
        u64             ino;
        loff_t          offset;
        int             namlen;
        unsigned int    d_type;
        char            name[];
};

struct readdir_data {
        struct dir_context ctx;
        char            *dirent;
        size_t          used;
        int             full;
};

static int nfsd_buffered_filldir(struct dir_context *ctx, const char *name,
                                 int namlen, loff_t offset, u64 ino,
                                 unsigned int d_type)
{
        struct readdir_data *buf =
                container_of(ctx, struct readdir_data, ctx);
        struct buffered_dirent *de = (void *)(buf->dirent + buf->used);
        unsigned int reclen;

        reclen = ALIGN(sizeof(struct buffered_dirent) + namlen, sizeof(u64));
        if (buf->used + reclen > PAGE_SIZE) {
                buf->full = 1;
                return -EINVAL;
        }

        de->namlen = namlen;
        de->offset = offset;
        de->ino = ino;
        de->d_type = d_type;
        memcpy(de->name, name, namlen);
        buf->used += reclen;

        return 0;
}

static __be32 nfsd_buffered_readdir(struct file *file, nfsd_filldir_t func,
                                    struct readdir_cd *cdp, loff_t *offsetp)
{
        struct buffered_dirent *de;
        int host_err;
        int size;
        loff_t offset;
        struct readdir_data buf = {
                .ctx.actor = nfsd_buffered_filldir,
                .dirent = (void *)__get_free_page(GFP_KERNEL)
        };

        if (!buf.dirent)
                return nfserrno(-ENOMEM);

        offset = *offsetp;

        while (1) {
                unsigned int reclen;

                cdp->err = nfserr_eof; /* will be cleared on successful read */
                buf.used = 0;
                buf.full = 0;

                host_err = iterate_dir(file, &buf.ctx);
                if (buf.full)
                        host_err = 0;

                if (host_err < 0)
                        break;

                size = buf.used;

                if (!size)
                        break;

                de = (struct buffered_dirent *)buf.dirent;
                while (size > 0) {
                        offset = de->offset;

                        if (func(cdp, de->name, de->namlen, de->offset,
                                 de->ino, de->d_type))
                                break;

                        if (cdp->err != nfs_ok)
                                break;

                        reclen = ALIGN(sizeof(*de) + de->namlen,
                                       sizeof(u64));
                        size -= reclen;
                        de = (struct buffered_dirent *)((char *)de + reclen);
                }
                if (size > 0) /* We bailed out early */
                        break;

                offset = vfs_llseek(file, 0, SEEK_CUR);
        }

        free_page((unsigned long)(buf.dirent));

        if (host_err)
                return nfserrno(host_err);

        *offsetp = offset;
        return cdp->err;
}

/*
 * Read entries from a directory.
 * The  NFSv3/4 verifier we ignore for now.
 */
__be32
nfsd_readdir(struct svc_rqst *rqstp, struct svc_fh *fhp, loff_t *offsetp, 
             struct readdir_cd *cdp, nfsd_filldir_t func)
{
        __be32          err;
        struct file     *file;
        loff_t          offset = *offsetp;
        int             may_flags = NFSD_MAY_READ;

        /* NFSv2 only supports 32 bit cookies */
        if (rqstp->rq_vers > 2)
                may_flags |= NFSD_MAY_64BIT_COOKIE;

        err = nfsd_open(rqstp, fhp, S_IFDIR, may_flags, &file);
        if (err)
                goto out;

        offset = vfs_llseek(file, offset, SEEK_SET);
        if (offset < 0) {
                err = nfserrno((int)offset);
                goto out_close;
        }

        err = nfsd_buffered_readdir(file, func, cdp, offsetp);

        if (err == nfserr_eof || err == nfserr_toosmall)
                err = nfs_ok; /* can still be found in ->err */
out_close:
        fput(file);
out:
        return err;
}

/*
 * Get file system stats
 * N.B. After this call fhp needs an fh_put
 */
__be32
nfsd_statfs(struct svc_rqst *rqstp, struct svc_fh *fhp, struct kstatfs *stat, int access)
{
        __be32 err;

        err = fh_verify(rqstp, fhp, 0, NFSD_MAY_NOP | access);
        if (!err) {
                struct path path = {
                        .mnt    = fhp->fh_export->ex_path.mnt,
                        .dentry = fhp->fh_dentry,
                };
                if (vfs_statfs(&path, stat))
                        err = nfserr_io;
        }
        return err;
}

static int exp_rdonly(struct svc_rqst *rqstp, struct svc_export *exp)
{
        return nfsexp_flags(rqstp, exp) & NFSEXP_READONLY;
}

#ifdef CONFIG_NFSD_V4
/*
 * Helper function to translate error numbers. In the case of xattr operations,
 * some error codes need to be translated outside of the standard translations.
 *
 * ENODATA needs to be translated to nfserr_noxattr.
 * E2BIG to nfserr_xattr2big.
 *
 * Additionally, vfs_listxattr can return -ERANGE. This means that the
 * file has too many extended attributes to retrieve inside an
 * XATTR_LIST_MAX sized buffer. This is a bug in the xattr implementation:
 * filesystems will allow the adding of extended attributes until they hit
 * their own internal limit. This limit may be larger than XATTR_LIST_MAX.
 * So, at that point, the attributes are present and valid, but can't
 * be retrieved using listxattr, since the upper level xattr code enforces
 * the XATTR_LIST_MAX limit.
 *
 * This bug means that we need to deal with listxattr returning -ERANGE. The
 * best mapping is to return TOOSMALL.
 */
static __be32
nfsd_xattr_errno(int err)
{
        switch (err) {
        case -ENODATA:
                return nfserr_noxattr;
        case -E2BIG:
                return nfserr_xattr2big;
        case -ERANGE:
                return nfserr_toosmall;
        }
        return nfserrno(err);
}

/*
 * Retrieve the specified user extended attribute. To avoid always
 * having to allocate the maximum size (since we are not getting
 * a maximum size from the RPC), do a probe + alloc. Hold a reader
 * lock on i_rwsem to prevent the extended attribute from changing
 * size while we're doing this.
 */
__be32
nfsd_getxattr(struct svc_rqst *rqstp, struct svc_fh *fhp, char *name,
              void **bufp, int *lenp)
{
        ssize_t len;
        __be32 err;
        char *buf;
        struct inode *inode;
        struct dentry *dentry;

        err = fh_verify(rqstp, fhp, 0, NFSD_MAY_READ);
        if (err)
                return err;

        err = nfs_ok;
        dentry = fhp->fh_dentry;
        inode = d_inode(dentry);

        inode_lock_shared(inode);

        len = vfs_getxattr(dentry, name, NULL, 0);

        /*
         * Zero-length attribute, just return.
         */
        if (len == 0) {
                *bufp = NULL;
                *lenp = 0;
                goto out;
        }

        if (len < 0) {
                err = nfsd_xattr_errno(len);
                goto out;
        }

        if (len > *lenp) {
                err = nfserr_toosmall;
                goto out;
        }

        buf = kvmalloc(len, GFP_KERNEL | GFP_NOFS);
        if (buf == NULL) {
                err = nfserr_jukebox;
                goto out;
        }

        len = vfs_getxattr(dentry, name, buf, len);
        if (len <= 0) {
                kvfree(buf);
                buf = NULL;
                err = nfsd_xattr_errno(len);
        }

        *lenp = len;
        *bufp = buf;

out:
        inode_unlock_shared(inode);

        return err;
}

/*
 * Retrieve the xattr names. Since we can't know how many are
 * user extended attributes, we must get all attributes here,
 * and have the XDR encode filter out the "user." ones.
 *
 * While this could always just allocate an XATTR_LIST_MAX
 * buffer, that's a waste, so do a probe + allocate. To
 * avoid any changes between the probe and allocate, wrap
 * this in inode_lock.
 */
__be32
nfsd_listxattr(struct svc_rqst *rqstp, struct svc_fh *fhp, char **bufp,
               int *lenp)
{
        ssize_t len;
        __be32 err;
        char *buf;
        struct inode *inode;
        struct dentry *dentry;

        err = fh_verify(rqstp, fhp, 0, NFSD_MAY_READ);
        if (err)
                return err;

        dentry = fhp->fh_dentry;
        inode = d_inode(dentry);
        *lenp = 0;

        inode_lock_shared(inode);

        len = vfs_listxattr(dentry, NULL, 0);
        if (len <= 0) {
                err = nfsd_xattr_errno(len);
                goto out;
        }

        if (len > XATTR_LIST_MAX) {
                err = nfserr_xattr2big;
                goto out;
        }

        /*
         * We're holding i_rwsem - use GFP_NOFS.
         */
        buf = kvmalloc(len, GFP_KERNEL | GFP_NOFS);
        if (buf == NULL) {
                err = nfserr_jukebox;
                goto out;
        }

        len = vfs_listxattr(dentry, buf, len);
        if (len <= 0) {
                kvfree(buf);
                err = nfsd_xattr_errno(len);
                goto out;
        }

        *lenp = len;
        *bufp = buf;

        err = nfs_ok;
out:
        inode_unlock_shared(inode);

        return err;
}

/*
 * Removexattr and setxattr need to call fh_lock to both lock the inode
 * and set the change attribute. Since the top-level vfs_removexattr
 * and vfs_setxattr calls already do their own inode_lock calls, call
 * the _locked variant. Pass in a NULL pointer for delegated_inode,
 * and let the client deal with NFS4ERR_DELAY (same as with e.g.
 * setattr and remove).
 */
__be32
nfsd_removexattr(struct svc_rqst *rqstp, struct svc_fh *fhp, char *name)
{
        __be32 err;
        int ret;

        err = fh_verify(rqstp, fhp, 0, NFSD_MAY_WRITE);
        if (err)
                return err;

        ret = fh_want_write(fhp);
        if (ret)
                return nfserrno(ret);

        fh_lock(fhp);

        ret = __vfs_removexattr_locked(fhp->fh_dentry, name, NULL);

        fh_unlock(fhp);
        fh_drop_write(fhp);

        return nfsd_xattr_errno(ret);
}

__be32
nfsd_setxattr(struct svc_rqst *rqstp, struct svc_fh *fhp, char *name,
              void *buf, u32 len, u32 flags)
{
        __be32 err;
        int ret;

        err = fh_verify(rqstp, fhp, 0, NFSD_MAY_WRITE);
        if (err)
                return err;

        ret = fh_want_write(fhp);
        if (ret)
                return nfserrno(ret);
        fh_lock(fhp);

        ret = __vfs_setxattr_locked(fhp->fh_dentry, name, buf, len, flags,
                                    NULL);

        fh_unlock(fhp);
        fh_drop_write(fhp);

        return nfsd_xattr_errno(ret);
}
#endif

/*
 * Check for a user's access permissions to this inode.
 */
__be32
nfsd_permission(struct svc_rqst *rqstp, struct svc_export *exp,
                                        struct dentry *dentry, int acc)
{
        struct inode    *inode = d_inode(dentry);
        int             err;

        if ((acc & NFSD_MAY_MASK) == NFSD_MAY_NOP)
                return 0;
#if 0
        dprintk("nfsd: permission 0x%x%s%s%s%s%s%s%s mode 0%o%s%s%s\n",
                acc,
                (acc & NFSD_MAY_READ)?  " read"  : "",
                (acc & NFSD_MAY_WRITE)? " write" : "",
                (acc & NFSD_MAY_EXEC)?  " exec"  : "",
                (acc & NFSD_MAY_SATTR)? " sattr" : "",
                (acc & NFSD_MAY_TRUNC)? " trunc" : "",
                (acc & NFSD_MAY_LOCK)?  " lock"  : "",
                (acc & NFSD_MAY_OWNER_OVERRIDE)? " owneroverride" : "",
                inode->i_mode,
                IS_IMMUTABLE(inode)?    " immut" : "",
                IS_APPEND(inode)?       " append" : "",
                __mnt_is_readonly(exp->ex_path.mnt)?    " ro" : "");
        dprintk("      owner %d/%d user %d/%d\n",
                inode->i_uid, inode->i_gid, current_fsuid(), current_fsgid());
#endif

        /* Normally we reject any write/sattr etc access on a read-only file
         * system.  But if it is IRIX doing check on write-access for a 
         * device special file, we ignore rofs.
         */
        if (!(acc & NFSD_MAY_LOCAL_ACCESS))
                if (acc & (NFSD_MAY_WRITE | NFSD_MAY_SATTR | NFSD_MAY_TRUNC)) {
                        if (exp_rdonly(rqstp, exp) ||
                            __mnt_is_readonly(exp->ex_path.mnt))
                                return nfserr_rofs;
                        if (/* (acc & NFSD_MAY_WRITE) && */ IS_IMMUTABLE(inode))
                                return nfserr_perm;
                }
        if ((acc & NFSD_MAY_TRUNC) && IS_APPEND(inode))
                return nfserr_perm;

        if (acc & NFSD_MAY_LOCK) {
                /* If we cannot rely on authentication in NLM requests,
                 * just allow locks, otherwise require read permission, or
                 * ownership
                 */
                if (exp->ex_flags & NFSEXP_NOAUTHNLM)
                        return 0;
                else
                        acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE;
        }
        /*
         * The file owner always gets access permission for accesses that
         * would normally be checked at open time. This is to make
         * file access work even when the client has done a fchmod(fd, 0).
         *
         * However, `cp foo bar' should fail nevertheless when bar is
         * readonly. A sensible way to do this might be to reject all
         * attempts to truncate a read-only file, because a creat() call
         * always implies file truncation.
         * ... but this isn't really fair.  A process may reasonably call
         * ftruncate on an open file descriptor on a file with perm 000.
         * We must trust the client to do permission checking - using "ACCESS"
         * with NFSv3.
         */
        if ((acc & NFSD_MAY_OWNER_OVERRIDE) &&
            uid_eq(inode->i_uid, current_fsuid()))
                return 0;

        /* This assumes  NFSD_MAY_{READ,WRITE,EXEC} == MAY_{READ,WRITE,EXEC} */
        err = inode_permission(inode, acc & (MAY_READ|MAY_WRITE|MAY_EXEC));

        /* Allow read access to binaries even when mode 111 */
        if (err == -EACCES && S_ISREG(inode->i_mode) &&
             (acc == (NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE) ||
              acc == (NFSD_MAY_READ | NFSD_MAY_READ_IF_EXEC)))
                err = inode_permission(inode, MAY_EXEC);

        return err? nfserrno(err) : 0;
}