[linux-2.6-microblaze.git] / include / linux / cgroup-defs.h

/* SPDX-License-Identifier: GPL-2.0 */
/*
 * linux/cgroup-defs.h - basic definitions for cgroup
 *
 * This file provides basic type and interface.  Include this file directly
 * only if necessary to avoid cyclic dependencies.
 */
#ifndef _LINUX_CGROUP_DEFS_H
#define _LINUX_CGROUP_DEFS_H

#include <linux/limits.h>
#include <linux/list.h>
#include <linux/idr.h>
#include <linux/wait.h>
#include <linux/mutex.h>
#include <linux/rcupdate.h>
#include <linux/refcount.h>
#include <linux/percpu-refcount.h>
#include <linux/percpu-rwsem.h>
#include <linux/u64_stats_sync.h>
#include <linux/workqueue.h>
#include <linux/bpf-cgroup.h>
#include <linux/psi_types.h>

#ifdef CONFIG_CGROUPS

struct cgroup;
struct cgroup_root;
struct cgroup_subsys;
struct cgroup_taskset;
struct kernfs_node;
struct kernfs_ops;
struct kernfs_open_file;
struct seq_file;
struct poll_table_struct;

#define MAX_CGROUP_TYPE_NAMELEN 32
#define MAX_CGROUP_ROOT_NAMELEN 64
#define MAX_CFTYPE_NAME         64

/* define the enumeration of all cgroup subsystems */
#define SUBSYS(_x) _x ## _cgrp_id,
enum cgroup_subsys_id {
#include <linux/cgroup_subsys.h>
        CGROUP_SUBSYS_COUNT,
};
#undef SUBSYS

/* bits in struct cgroup_subsys_state flags field */
enum {
        CSS_NO_REF      = (1 << 0), /* no reference counting for this css */
        CSS_ONLINE      = (1 << 1), /* between ->css_online() and ->css_offline() */
        CSS_RELEASED    = (1 << 2), /* refcnt reached zero, released */
        CSS_VISIBLE     = (1 << 3), /* css is visible to userland */
        CSS_DYING       = (1 << 4), /* css is dying */
};

/* bits in struct cgroup flags field */
enum {
        /* Control Group requires release notifications to userspace */
        CGRP_NOTIFY_ON_RELEASE,
        /*
         * Clone the parent's configuration when creating a new child
         * cpuset cgroup.  For historical reasons, this option can be
         * specified at mount time and thus is implemented here.
         */
        CGRP_CPUSET_CLONE_CHILDREN,
};

/* cgroup_root->flags */
enum {
        CGRP_ROOT_NOPREFIX      = (1 << 1), /* mounted subsystems have no named prefix */
        CGRP_ROOT_XATTR         = (1 << 2), /* supports extended attributes */

        /*
         * Consider namespaces as delegation boundaries.  If this flag is
         * set, controller specific interface files in a namespace root
         * aren't writeable from inside the namespace.
         */
        CGRP_ROOT_NS_DELEGATE   = (1 << 3),

        /*
         * Enable cpuset controller in v1 cgroup to use v2 behavior.
         */
        CGRP_ROOT_CPUSET_V2_MODE = (1 << 4),
};

/* cftype->flags */
enum {
        CFTYPE_ONLY_ON_ROOT     = (1 << 0),     /* only create on root cgrp */
        CFTYPE_NOT_ON_ROOT      = (1 << 1),     /* don't create on root cgrp */
        CFTYPE_NS_DELEGATABLE   = (1 << 2),     /* writeable beyond delegation boundaries */

        CFTYPE_NO_PREFIX        = (1 << 3),     /* (DON'T USE FOR NEW FILES) no subsys prefix */
        CFTYPE_WORLD_WRITABLE   = (1 << 4),     /* (DON'T USE FOR NEW FILES) S_IWUGO */
        CFTYPE_DEBUG            = (1 << 5),     /* create when cgroup_debug */

        /* internal flags, do not use outside cgroup core proper */
        __CFTYPE_ONLY_ON_DFL    = (1 << 16),    /* only on default hierarchy */
        __CFTYPE_NOT_ON_DFL     = (1 << 17),    /* not on default hierarchy */
};

/*
 * cgroup_file is the handle for a file instance created in a cgroup which
 * is used, for example, to generate file changed notifications.  This can
 * be obtained by setting cftype->file_offset.
 */
struct cgroup_file {
        /* do not access any fields from outside cgroup core */
        struct kernfs_node *kn;
        unsigned long notified_at;
        struct timer_list notify_timer;
};

/*
 * Per-subsystem/per-cgroup state maintained by the system.  This is the
 * fundamental structural building block that controllers deal with.
 *
 * Fields marked with "PI:" are public and immutable and may be accessed
 * directly without synchronization.
 */
struct cgroup_subsys_state {
        /* PI: the cgroup that this css is attached to */
        struct cgroup *cgroup;

        /* PI: the cgroup subsystem that this css is attached to */
        struct cgroup_subsys *ss;

        /* reference count - access via css_[try]get() and css_put() */
        struct percpu_ref refcnt;

        /* siblings list anchored at the parent's ->children */
        struct list_head sibling;
        struct list_head children;

        /* flush target list anchored at cgrp->rstat_css_list */
        struct list_head rstat_css_node;

        /*
         * PI: Subsys-unique ID.  0 is unused and root is always 1.  The
         * matching css can be looked up using css_from_id().
         */
        int id;

        unsigned int flags;

        /*
         * Monotonically increasing unique serial number which defines a
         * uniform order among all csses.  It's guaranteed that all
         * ->children lists are in the ascending order of ->serial_nr and
         * used to allow interrupting and resuming iterations.
         */
        u64 serial_nr;

        /*
         * Incremented by online self and children.  Used to guarantee that
         * parents are not offlined before their children.
         */
        atomic_t online_cnt;

        /* percpu_ref killing and RCU release */
        struct work_struct destroy_work;
        struct rcu_work destroy_rwork;

        /*
         * PI: the parent css.  Placed here for cache proximity to following
         * fields of the containing structure.
         */
        struct cgroup_subsys_state *parent;
};

/*
 * A css_set is a structure holding pointers to a set of
 * cgroup_subsys_state objects. This saves space in the task struct
 * object and speeds up fork()/exit(), since a single inc/dec and a
 * list_add()/del() can bump the reference count on the entire cgroup
 * set for a task.
 */
struct css_set {
        /*
         * Set of subsystem states, one for each subsystem. This array is
         * immutable after creation apart from the init_css_set during
         * subsystem registration (at boot time).
         */
        struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];

        /* reference count */
        refcount_t refcount;

        /*
         * For a domain cgroup, the following points to self.  If threaded,
         * to the matching cset of the nearest domain ancestor.  The
         * dom_cset provides access to the domain cgroup and its csses to
         * which domain level resource consumptions should be charged.
         */
        struct css_set *dom_cset;

        /* the default cgroup associated with this css_set */
        struct cgroup *dfl_cgrp;

        /* internal task count, protected by css_set_lock */
        int nr_tasks;

        /*
         * Lists running through all tasks using this cgroup group.
         * mg_tasks lists tasks which belong to this cset but are in the
         * process of being migrated out or in.  Protected by
         * css_set_rwsem, but, during migration, once tasks are moved to
         * mg_tasks, it can be read safely while holding cgroup_mutex.
         */
        struct list_head tasks;
        struct list_head mg_tasks;

        /* all css_task_iters currently walking this cset */
        struct list_head task_iters;

        /*
         * On the default hierarhcy, ->subsys[ssid] may point to a css
         * attached to an ancestor instead of the cgroup this css_set is
         * associated with.  The following node is anchored at
         * ->subsys[ssid]->cgroup->e_csets[ssid] and provides a way to
         * iterate through all css's attached to a given cgroup.
         */
        struct list_head e_cset_node[CGROUP_SUBSYS_COUNT];

        /* all threaded csets whose ->dom_cset points to this cset */
        struct list_head threaded_csets;
        struct list_head threaded_csets_node;

        /*
         * List running through all cgroup groups in the same hash
         * slot. Protected by css_set_lock
         */
        struct hlist_node hlist;

        /*
         * List of cgrp_cset_links pointing at cgroups referenced from this
         * css_set.  Protected by css_set_lock.
         */
        struct list_head cgrp_links;

        /*
         * List of csets participating in the on-going migration either as
         * source or destination.  Protected by cgroup_mutex.
         */
        struct list_head mg_preload_node;
        struct list_head mg_node;

        /*
         * If this cset is acting as the source of migration the following
         * two fields are set.  mg_src_cgrp and mg_dst_cgrp are
         * respectively the source and destination cgroups of the on-going
         * migration.  mg_dst_cset is the destination cset the target tasks
         * on this cset should be migrated to.  Protected by cgroup_mutex.
         */
        struct cgroup *mg_src_cgrp;
        struct cgroup *mg_dst_cgrp;
        struct css_set *mg_dst_cset;

        /* dead and being drained, ignore for migration */
        bool dead;

        /* For RCU-protected deletion */
        struct rcu_head rcu_head;
};

struct cgroup_base_stat {
        struct task_cputime cputime;
};

/*
 * rstat - cgroup scalable recursive statistics.  Accounting is done
 * per-cpu in cgroup_rstat_cpu which is then lazily propagated up the
 * hierarchy on reads.
 *
 * When a stat gets updated, the cgroup_rstat_cpu and its ancestors are
 * linked into the updated tree.  On the following read, propagation only
 * considers and consumes the updated tree.  This makes reading O(the
 * number of descendants which have been active since last read) instead of
 * O(the total number of descendants).
 *
 * This is important because there can be a lot of (draining) cgroups which
 * aren't active and stat may be read frequently.  The combination can
 * become very expensive.  By propagating selectively, increasing reading
 * frequency decreases the cost of each read.
 *
 * This struct hosts both the fields which implement the above -
 * updated_children and updated_next - and the fields which track basic
 * resource statistics on top of it - bsync, bstat and last_bstat.
 */
struct cgroup_rstat_cpu {
        /*
         * ->bsync protects ->bstat.  These are the only fields which get
         * updated in the hot path.
         */
        struct u64_stats_sync bsync;
        struct cgroup_base_stat bstat;

        /*
         * Snapshots at the last reading.  These are used to calculate the
         * deltas to propagate to the global counters.
         */
        struct cgroup_base_stat last_bstat;

        /*
         * Child cgroups with stat updates on this cpu since the last read
         * are linked on the parent's ->updated_children through
         * ->updated_next.
         *
         * In addition to being more compact, singly-linked list pointing
         * to the cgroup makes it unnecessary for each per-cpu struct to
         * point back to the associated cgroup.
         *
         * Protected by per-cpu cgroup_rstat_cpu_lock.
         */
        struct cgroup *updated_children;        /* terminated by self cgroup */
        struct cgroup *updated_next;            /* NULL iff not on the list */
};

struct cgroup {
        /* self css with NULL ->ss, points back to this cgroup */
        struct cgroup_subsys_state self;

        unsigned long flags;            /* "unsigned long" so bitops work */

        /*
         * idr allocated in-hierarchy ID.
         *
         * ID 0 is not used, the ID of the root cgroup is always 1, and a
         * new cgroup will be assigned with a smallest available ID.
         *
         * Allocating/Removing ID must be protected by cgroup_mutex.
         */
        int id;

        /*
         * The depth this cgroup is at.  The root is at depth zero and each
         * step down the hierarchy increments the level.  This along with
         * ancestor_ids[] can determine whether a given cgroup is a
         * descendant of another without traversing the hierarchy.
         */
        int level;

        /* Maximum allowed descent tree depth */
        int max_depth;

        /*
         * Keep track of total numbers of visible and dying descent cgroups.
         * Dying cgroups are cgroups which were deleted by a user,
         * but are still existing because someone else is holding a reference.
         * max_descendants is a maximum allowed number of descent cgroups.
         *
         * nr_descendants and nr_dying_descendants are protected
         * by cgroup_mutex and css_set_lock. It's fine to read them holding
         * any of cgroup_mutex and css_set_lock; for writing both locks
         * should be held.
         */
        int nr_descendants;
        int nr_dying_descendants;
        int max_descendants;

        /*
         * Each non-empty css_set associated with this cgroup contributes
         * one to nr_populated_csets.  The counter is zero iff this cgroup
         * doesn't have any tasks.
         *
         * All children which have non-zero nr_populated_csets and/or
         * nr_populated_children of their own contribute one to either
         * nr_populated_domain_children or nr_populated_threaded_children
         * depending on their type.  Each counter is zero iff all cgroups
         * of the type in the subtree proper don't have any tasks.
         */
        int nr_populated_csets;
        int nr_populated_domain_children;
        int nr_populated_threaded_children;

        int nr_threaded_children;       /* # of live threaded child cgroups */

        struct kernfs_node *kn;         /* cgroup kernfs entry */
        struct cgroup_file procs_file;  /* handle for "cgroup.procs" */
        struct cgroup_file events_file; /* handle for "cgroup.events" */

        /*
         * The bitmask of subsystems enabled on the child cgroups.
         * ->subtree_control is the one configured through
         * "cgroup.subtree_control" while ->child_ss_mask is the effective
         * one which may have more subsystems enabled.  Controller knobs
         * are made available iff it's enabled in ->subtree_control.
         */
        u16 subtree_control;
        u16 subtree_ss_mask;
        u16 old_subtree_control;
        u16 old_subtree_ss_mask;

        /* Private pointers for each registered subsystem */
        struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];

        struct cgroup_root *root;

        /*
         * List of cgrp_cset_links pointing at css_sets with tasks in this
         * cgroup.  Protected by css_set_lock.
         */
        struct list_head cset_links;

        /*
         * On the default hierarchy, a css_set for a cgroup with some
         * susbsys disabled will point to css's which are associated with
         * the closest ancestor which has the subsys enabled.  The
         * following lists all css_sets which point to this cgroup's css
         * for the given subsystem.
         */
        struct list_head e_csets[CGROUP_SUBSYS_COUNT];

        /*
         * If !threaded, self.  If threaded, it points to the nearest
         * domain ancestor.  Inside a threaded subtree, cgroups are exempt
         * from process granularity and no-internal-task constraint.
         * Domain level resource consumptions which aren't tied to a
         * specific task are charged to the dom_cgrp.
         */
        struct cgroup *dom_cgrp;
        struct cgroup *old_dom_cgrp;            /* used while enabling threaded */

        /* per-cpu recursive resource statistics */
        struct cgroup_rstat_cpu __percpu *rstat_cpu;
        struct list_head rstat_css_list;

        /* cgroup basic resource statistics */
        struct cgroup_base_stat pending_bstat;  /* pending from children */
        struct cgroup_base_stat bstat;
        struct prev_cputime prev_cputime;       /* for printing out cputime */

        /*
         * list of pidlists, up to two for each namespace (one for procs, one
         * for tasks); created on demand.
         */
        struct list_head pidlists;
        struct mutex pidlist_mutex;

        /* used to wait for offlining of csses */
        wait_queue_head_t offline_waitq;

        /* used to schedule release agent */
        struct work_struct release_agent_work;

        /* used to track pressure stalls */
        struct psi_group psi;

        /* used to store eBPF programs */
        struct cgroup_bpf bpf;

        /* If there is block congestion on this cgroup. */
        atomic_t congestion_count;

        /* ids of the ancestors at each level including self */
        int ancestor_ids[];
};

/*
 * A cgroup_root represents the root of a cgroup hierarchy, and may be
 * associated with a kernfs_root to form an active hierarchy.  This is
 * internal to cgroup core.  Don't access directly from controllers.
 */
struct cgroup_root {
        struct kernfs_root *kf_root;

        /* The bitmask of subsystems attached to this hierarchy */
        unsigned int subsys_mask;

        /* Unique id for this hierarchy. */
        int hierarchy_id;

        /* The root cgroup.  Root is destroyed on its release. */
        struct cgroup cgrp;

        /* for cgrp->ancestor_ids[0] */
        int cgrp_ancestor_id_storage;

        /* Number of cgroups in the hierarchy, used only for /proc/cgroups */
        atomic_t nr_cgrps;

        /* A list running through the active hierarchies */
        struct list_head root_list;

        /* Hierarchy-specific flags */
        unsigned int flags;

        /* IDs for cgroups in this hierarchy */
        struct idr cgroup_idr;

        /* The path to use for release notifications. */
        char release_agent_path[PATH_MAX];

        /* The name for this hierarchy - may be empty */
        char name[MAX_CGROUP_ROOT_NAMELEN];
};

/*
 * struct cftype: handler definitions for cgroup control files
 *
 * When reading/writing to a file:
 *      - the cgroup to use is file->f_path.dentry->d_parent->d_fsdata
 *      - the 'cftype' of the file is file->f_path.dentry->d_fsdata
 */
struct cftype {
        /*
         * By convention, the name should begin with the name of the
         * subsystem, followed by a period.  Zero length string indicates
         * end of cftype array.
         */
        char name[MAX_CFTYPE_NAME];
        unsigned long private;

        /*
         * The maximum length of string, excluding trailing nul, that can
         * be passed to write.  If < PAGE_SIZE-1, PAGE_SIZE-1 is assumed.
         */
        size_t max_write_len;

        /* CFTYPE_* flags */
        unsigned int flags;

        /*
         * If non-zero, should contain the offset from the start of css to
         * a struct cgroup_file field.  cgroup will record the handle of
         * the created file into it.  The recorded handle can be used as
         * long as the containing css remains accessible.
         */
        unsigned int file_offset;

        /*
         * Fields used for internal bookkeeping.  Initialized automatically
         * during registration.
         */
        struct cgroup_subsys *ss;       /* NULL for cgroup core files */
        struct list_head node;          /* anchored at ss->cfts */
        struct kernfs_ops *kf_ops;

        int (*open)(struct kernfs_open_file *of);
        void (*release)(struct kernfs_open_file *of);

        /*
         * read_u64() is a shortcut for the common case of returning a
         * single integer. Use it in place of read()
         */
        u64 (*read_u64)(struct cgroup_subsys_state *css, struct cftype *cft);
        /*
         * read_s64() is a signed version of read_u64()
         */
        s64 (*read_s64)(struct cgroup_subsys_state *css, struct cftype *cft);

        /* generic seq_file read interface */
        int (*seq_show)(struct seq_file *sf, void *v);

        /* optional ops, implement all or none */
        void *(*seq_start)(struct seq_file *sf, loff_t *ppos);
        void *(*seq_next)(struct seq_file *sf, void *v, loff_t *ppos);
        void (*seq_stop)(struct seq_file *sf, void *v);

        /*
         * write_u64() is a shortcut for the common case of accepting
         * a single integer (as parsed by simple_strtoull) from
         * userspace. Use in place of write(); return 0 or error.
         */
        int (*write_u64)(struct cgroup_subsys_state *css, struct cftype *cft,
                         u64 val);
        /*
         * write_s64() is a signed version of write_u64()
         */
        int (*write_s64)(struct cgroup_subsys_state *css, struct cftype *cft,
                         s64 val);

        /*
         * write() is the generic write callback which maps directly to
         * kernfs write operation and overrides all other operations.
         * Maximum write size is determined by ->max_write_len.  Use
         * of_css/cft() to access the associated css and cft.
         */
        ssize_t (*write)(struct kernfs_open_file *of,
                         char *buf, size_t nbytes, loff_t off);

        __poll_t (*poll)(struct kernfs_open_file *of,
                         struct poll_table_struct *pt);

#ifdef CONFIG_DEBUG_LOCK_ALLOC
        struct lock_class_key   lockdep_key;
#endif
};

/*
 * Control Group subsystem type.
 * See Documentation/cgroup-v1/cgroups.txt for details
 */
struct cgroup_subsys {
        struct cgroup_subsys_state *(*css_alloc)(struct cgroup_subsys_state *parent_css);
        int (*css_online)(struct cgroup_subsys_state *css);
        void (*css_offline)(struct cgroup_subsys_state *css);
        void (*css_released)(struct cgroup_subsys_state *css);
        void (*css_free)(struct cgroup_subsys_state *css);
        void (*css_reset)(struct cgroup_subsys_state *css);
        void (*css_rstat_flush)(struct cgroup_subsys_state *css, int cpu);
        int (*css_extra_stat_show)(struct seq_file *seq,
                                   struct cgroup_subsys_state *css);

        int (*can_attach)(struct cgroup_taskset *tset);
        void (*cancel_attach)(struct cgroup_taskset *tset);
        void (*attach)(struct cgroup_taskset *tset);
        void (*post_attach)(void);
        int (*can_fork)(struct task_struct *task);
        void (*cancel_fork)(struct task_struct *task);
        void (*fork)(struct task_struct *task);
        void (*exit)(struct task_struct *task);
        void (*release)(struct task_struct *task);
        void (*bind)(struct cgroup_subsys_state *root_css);

        bool early_init:1;

        /*
         * If %true, the controller, on the default hierarchy, doesn't show
         * up in "cgroup.controllers" or "cgroup.subtree_control", is
         * implicitly enabled on all cgroups on the default hierarchy, and
         * bypasses the "no internal process" constraint.  This is for
         * utility type controllers which is transparent to userland.
         *
         * An implicit controller can be stolen from the default hierarchy
         * anytime and thus must be okay with offline csses from previous
         * hierarchies coexisting with csses for the current one.
         */
        bool implicit_on_dfl:1;

        /*
         * If %true, the controller, supports threaded mode on the default
         * hierarchy.  In a threaded subtree, both process granularity and
         * no-internal-process constraint are ignored and a threaded
         * controllers should be able to handle that.
         *
         * Note that as an implicit controller is automatically enabled on
         * all cgroups on the default hierarchy, it should also be
         * threaded.  implicit && !threaded is not supported.
         */
        bool threaded:1;

        /*
         * If %false, this subsystem is properly hierarchical -
         * configuration, resource accounting and restriction on a parent
         * cgroup cover those of its children.  If %true, hierarchy support
         * is broken in some ways - some subsystems ignore hierarchy
         * completely while others are only implemented half-way.
         *
         * It's now disallowed to create nested cgroups if the subsystem is
         * broken and cgroup core will emit a warning message on such
         * cases.  Eventually, all subsystems will be made properly
         * hierarchical and this will go away.
         */
        bool broken_hierarchy:1;
        bool warned_broken_hierarchy:1;

        /* the following two fields are initialized automtically during boot */
        int id;
        const char *name;

        /* optional, initialized automatically during boot if not set */
        const char *legacy_name;

        /* link to parent, protected by cgroup_lock() */
        struct cgroup_root *root;

        /* idr for css->id */
        struct idr css_idr;

        /*
         * List of cftypes.  Each entry is the first entry of an array
         * terminated by zero length name.
         */
        struct list_head cfts;

        /*
         * Base cftypes which are automatically registered.  The two can
         * point to the same array.
         */
        struct cftype *dfl_cftypes;     /* for the default hierarchy */
        struct cftype *legacy_cftypes;  /* for the legacy hierarchies */

        /*
         * A subsystem may depend on other subsystems.  When such subsystem
         * is enabled on a cgroup, the depended-upon subsystems are enabled
         * together if available.  Subsystems enabled due to dependency are
         * not visible to userland until explicitly enabled.  The following
         * specifies the mask of subsystems that this one depends on.
         */
        unsigned int depends_on;
};

extern struct percpu_rw_semaphore cgroup_threadgroup_rwsem;

/**
 * cgroup_threadgroup_change_begin - threadgroup exclusion for cgroups
 * @tsk: target task
 *
 * Allows cgroup operations to synchronize against threadgroup changes
 * using a percpu_rw_semaphore.
 */
static inline void cgroup_threadgroup_change_begin(struct task_struct *tsk)
{
        percpu_down_read(&cgroup_threadgroup_rwsem);
}

/**
 * cgroup_threadgroup_change_end - threadgroup exclusion for cgroups
 * @tsk: target task
 *
 * Counterpart of cgroup_threadcgroup_change_begin().
 */
static inline void cgroup_threadgroup_change_end(struct task_struct *tsk)
{
        percpu_up_read(&cgroup_threadgroup_rwsem);
}

#else   /* CONFIG_CGROUPS */

#define CGROUP_SUBSYS_COUNT 0

static inline void cgroup_threadgroup_change_begin(struct task_struct *tsk)
{
        might_sleep();
}

static inline void cgroup_threadgroup_change_end(struct task_struct *tsk) {}

#endif  /* CONFIG_CGROUPS */

#ifdef CONFIG_SOCK_CGROUP_DATA

/*
 * sock_cgroup_data is embedded at sock->sk_cgrp_data and contains
 * per-socket cgroup information except for memcg association.
 *
 * On legacy hierarchies, net_prio and net_cls controllers directly set
 * attributes on each sock which can then be tested by the network layer.
 * On the default hierarchy, each sock is associated with the cgroup it was
 * created in and the networking layer can match the cgroup directly.
 *
 * To avoid carrying all three cgroup related fields separately in sock,
 * sock_cgroup_data overloads (prioidx, classid) and the cgroup pointer.
 * On boot, sock_cgroup_data records the cgroup that the sock was created
 * in so that cgroup2 matches can be made; however, once either net_prio or
 * net_cls starts being used, the area is overriden to carry prioidx and/or
 * classid.  The two modes are distinguished by whether the lowest bit is
 * set.  Clear bit indicates cgroup pointer while set bit prioidx and
 * classid.
 *
 * While userland may start using net_prio or net_cls at any time, once
 * either is used, cgroup2 matching no longer works.  There is no reason to
 * mix the two and this is in line with how legacy and v2 compatibility is
 * handled.  On mode switch, cgroup references which are already being
 * pointed to by socks may be leaked.  While this can be remedied by adding
 * synchronization around sock_cgroup_data, given that the number of leaked
 * cgroups is bound and highly unlikely to be high, this seems to be the
 * better trade-off.
 */
struct sock_cgroup_data {
        union {
#ifdef __LITTLE_ENDIAN
                struct {
                        u8      is_data;
                        u8      padding;
                        u16     prioidx;
                        u32     classid;
                } __packed;
#else
                struct {
                        u32     classid;
                        u16     prioidx;
                        u8      padding;
                        u8      is_data;
                } __packed;
#endif
                u64             val;
        };
};

/*
 * There's a theoretical window where the following accessors race with
 * updaters and return part of the previous pointer as the prioidx or
 * classid.  Such races are short-lived and the result isn't critical.
 */
static inline u16 sock_cgroup_prioidx(const struct sock_cgroup_data *skcd)
{
        /* fallback to 1 which is always the ID of the root cgroup */
        return (skcd->is_data & 1) ? skcd->prioidx : 1;
}

static inline u32 sock_cgroup_classid(const struct sock_cgroup_data *skcd)
{
        /* fallback to 0 which is the unconfigured default classid */
        return (skcd->is_data & 1) ? skcd->classid : 0;
}

/*
 * If invoked concurrently, the updaters may clobber each other.  The
 * caller is responsible for synchronization.
 */
static inline void sock_cgroup_set_prioidx(struct sock_cgroup_data *skcd,
                                           u16 prioidx)
{
        struct sock_cgroup_data skcd_buf = {{ .val = READ_ONCE(skcd->val) }};

        if (sock_cgroup_prioidx(&skcd_buf) == prioidx)
                return;

        if (!(skcd_buf.is_data & 1)) {
                skcd_buf.val = 0;
                skcd_buf.is_data = 1;
        }

        skcd_buf.prioidx = prioidx;
        WRITE_ONCE(skcd->val, skcd_buf.val);    /* see sock_cgroup_ptr() */
}

static inline void sock_cgroup_set_classid(struct sock_cgroup_data *skcd,
                                           u32 classid)
{
        struct sock_cgroup_data skcd_buf = {{ .val = READ_ONCE(skcd->val) }};

        if (sock_cgroup_classid(&skcd_buf) == classid)
                return;

        if (!(skcd_buf.is_data & 1)) {
                skcd_buf.val = 0;
                skcd_buf.is_data = 1;
        }

        skcd_buf.classid = classid;
        WRITE_ONCE(skcd->val, skcd_buf.val);    /* see sock_cgroup_ptr() */
}

#else   /* CONFIG_SOCK_CGROUP_DATA */

struct sock_cgroup_data {
};

#endif  /* CONFIG_SOCK_CGROUP_DATA */

#endif  /* _LINUX_CGROUP_DEFS_H */