to find potential names, and matches inode numbers to find the correct
match.
+ flags
+ Some filesystems may need to be handled differently than others. The
+ export_operations struct also includes a flags field that allows the
+ filesystem to communicate such information to nfsd. See the Export
+ Operations Flags section below for more explanation.
A filehandle fragment consists of an array of 1 or more 4byte words,
together with a one byte "type".
nuls. Rather, the encode_fh routine should choose a "type" which
indicates the decode_fh how much of the filehandle is valid, and how
it should be interpreted.
+
+Export Operations Flags
+-----------------------
+In addition to the operation vector pointers, struct export_operations also
+contains a "flags" field that allows the filesystem to communicate to nfsd
+that it may want to do things differently when dealing with it. The
+following flags are defined:
+
+ EXPORT_OP_NOWCC - disable NFSv3 WCC attributes on this filesystem
+ RFC 1813 recommends that servers always send weak cache consistency
+ (WCC) data to the client after each operation. The server should
+ atomically collect attributes about the inode, do an operation on it,
+ and then collect the attributes afterward. This allows the client to
+ skip issuing GETATTRs in some situations but means that the server
+ is calling vfs_getattr for almost all RPCs. On some filesystems
+ (particularly those that are clustered or networked) this is expensive
+ and atomicity is difficult to guarantee. This flag indicates to nfsd
+ that it should skip providing WCC attributes to the client in NFSv3
+ replies when doing operations on this filesystem. Consider enabling
+ this on filesystems that have an expensive ->getattr inode operation,
+ or when atomicity between pre and post operation attribute collection
+ is impossible to guarantee.
+
+ EXPORT_OP_NOSUBTREECHK - disallow subtree checking on this fs
+ Many NFS operations deal with filehandles, which the server must then
+ vet to ensure that they live inside of an exported tree. When the
+ export consists of an entire filesystem, this is trivial. nfsd can just
+ ensure that the filehandle live on the filesystem. When only part of a
+ filesystem is exported however, then nfsd must walk the ancestors of the
+ inode to ensure that it's within an exported subtree. This is an
+ expensive operation and not all filesystems can support it properly.
+ This flag exempts the filesystem from subtree checking and causes
+ exportfs to get back an error if it tries to enable subtree checking
+ on it.
+
+ EXPORT_OP_CLOSE_BEFORE_UNLINK - always close cached files before unlinking
+ On some exportable filesystems (such as NFS) unlinking a file that
+ is still open can cause a fair bit of extra work. For instance,
+ the NFS client will do a "sillyrename" to ensure that the file
+ sticks around while it's still open. When reexporting, that open
+ file is held by nfsd so we usually end up doing a sillyrename, and
+ then immediately deleting the sillyrenamed file just afterward when
+ the link count actually goes to zero. Sometimes this delete can race
+ with other operations (for instance an rmdir of the parent directory).
+ This flag causes nfsd to close any open files for this inode _before_
+ calling into the vfs to do an unlink or a rename that would replace
+ an existing file.
projects / linux-2.6-microblaze.git / blobdiff