Merge branch 'docs-next' of git://git.lwn.net/linux-2.6

[linux-2.6/next.git] / include / linux / fsnotify_backend.h

/*
 * Filesystem access notification for Linux
 *
 *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
 */

#ifndef __LINUX_FSNOTIFY_BACKEND_H
#define __LINUX_FSNOTIFY_BACKEND_H

#ifdef __KERNEL__

#include <linux/idr.h> /* inotify uses this */
#include <linux/fs.h> /* struct inode */
#include <linux/list.h>
#include <linux/path.h> /* struct path */
#include <linux/spinlock.h>
#include <linux/types.h>

#include <asm/atomic.h>

/*
 * IN_* from inotfy.h lines up EXACTLY with FS_*, this is so we can easily
 * convert between them.  dnotify only needs conversion at watch creation
 * so no perf loss there.  fanotify isn't defined yet, so it can use the
 * wholes if it needs more events.
 */
#define FS_ACCESS               0x00000001      /* File was accessed */
#define FS_MODIFY               0x00000002      /* File was modified */
#define FS_ATTRIB               0x00000004      /* Metadata changed */
#define FS_CLOSE_WRITE          0x00000008      /* Writtable file was closed */
#define FS_CLOSE_NOWRITE        0x00000010      /* Unwrittable file closed */
#define FS_OPEN                 0x00000020      /* File was opened */
#define FS_MOVED_FROM           0x00000040      /* File was moved from X */
#define FS_MOVED_TO             0x00000080      /* File was moved to Y */
#define FS_CREATE               0x00000100      /* Subfile was created */
#define FS_DELETE               0x00000200      /* Subfile was deleted */
#define FS_DELETE_SELF          0x00000400      /* Self was deleted */
#define FS_MOVE_SELF            0x00000800      /* Self was moved */

#define FS_UNMOUNT              0x00002000      /* inode on umount fs */
#define FS_Q_OVERFLOW           0x00004000      /* Event queued overflowed */
#define FS_IN_IGNORED           0x00008000      /* last inotify event here */

#define FS_IN_ISDIR             0x40000000      /* event occurred against dir */
#define FS_IN_ONESHOT           0x80000000      /* only send event once */

#define FS_DN_RENAME            0x10000000      /* file renamed */
#define FS_DN_MULTISHOT         0x20000000      /* dnotify multishot */

/* This inode cares about things that happen to its children.  Always set for
 * dnotify and inotify. */
#define FS_EVENT_ON_CHILD       0x08000000

/* This is a list of all events that may get sent to a parernt based on fs event
 * happening to inodes inside that directory */
#define FS_EVENTS_POSS_ON_CHILD   (FS_ACCESS | FS_MODIFY | FS_ATTRIB |\
                                   FS_CLOSE_WRITE | FS_CLOSE_NOWRITE | FS_OPEN |\
                                   FS_MOVED_FROM | FS_MOVED_TO | FS_CREATE |\
                                   FS_DELETE)

/* listeners that hard code group numbers near the top */
#define DNOTIFY_GROUP_NUM       UINT_MAX
#define INOTIFY_GROUP_NUM       (DNOTIFY_GROUP_NUM-1)

struct fsnotify_group;
struct fsnotify_event;
struct fsnotify_mark_entry;
struct fsnotify_event_private_data;

/*
 * Each group much define these ops.  The fsnotify infrastructure will call
 * these operations for each relevant group.
 *
 * should_send_event - given a group, inode, and mask this function determines
 *              if the group is interested in this event.
 * handle_event - main call for a group to handle an fs event
 * free_group_priv - called when a group refcnt hits 0 to clean up the private union
 * freeing-mark - this means that a mark has been flagged to die when everything
 *              finishes using it.  The function is supplied with what must be a
 *              valid group and inode to use to clean up.
 */
struct fsnotify_ops {
        bool (*should_send_event)(struct fsnotify_group *group, struct inode *inode, __u32 mask);
        int (*handle_event)(struct fsnotify_group *group, struct fsnotify_event *event);
        void (*free_group_priv)(struct fsnotify_group *group);
        void (*freeing_mark)(struct fsnotify_mark_entry *entry, struct fsnotify_group *group);
        void (*free_event_priv)(struct fsnotify_event_private_data *priv);
};

/*
 * A group is a "thing" that wants to receive notification about filesystem
 * events.  The mask holds the subset of event types this group cares about.
 * refcnt on a group is up to the implementor and at any moment if it goes 0
 * everything will be cleaned up.
 */
struct fsnotify_group {
        /*
         * global list of all groups receiving events from fsnotify.
         * anchored by fsnotify_groups and protected by either fsnotify_grp_mutex
         * or fsnotify_grp_srcu depending on write vs read.
         */
        struct list_head group_list;

        /*
         * Defines all of the event types in which this group is interested.
         * This mask is a bitwise OR of the FS_* events from above.  Each time
         * this mask changes for a group (if it changes) the correct functions
         * must be called to update the global structures which indicate global
         * interest in event types.
         */
        __u32 mask;

        /*
         * How the refcnt is used is up to each group.  When the refcnt hits 0
         * fsnotify will clean up all of the resources associated with this group.
         * As an example, the dnotify group will always have a refcnt=1 and that
         * will never change.  Inotify, on the other hand, has a group per
         * inotify_init() and the refcnt will hit 0 only when that fd has been
         * closed.
         */
        atomic_t refcnt;                /* things with interest in this group */
        unsigned int group_num;         /* simply prevents accidental group collision */

        const struct fsnotify_ops *ops; /* how this group handles things */

        /* needed to send notification to userspace */
        struct mutex notification_mutex;        /* protect the notification_list */
        struct list_head notification_list;     /* list of event_holder this group needs to send to userspace */
        wait_queue_head_t notification_waitq;   /* read() on the notification file blocks on this waitq */
        unsigned int q_len;                     /* events on the queue */
        unsigned int max_events;                /* maximum events allowed on the list */

        /* stores all fastapth entries assoc with this group so they can be cleaned on unregister */
        spinlock_t mark_lock;           /* protect mark_entries list */
        atomic_t num_marks;             /* 1 for each mark entry and 1 for not being
                                         * past the point of no return when freeing
                                         * a group */
        struct list_head mark_entries;  /* all inode mark entries for this group */

        /* prevents double list_del of group_list.  protected by global fsnotify_grp_mutex */
        bool on_group_list;

        /* groups can define private fields here or use the void *private */
        union {
                void *private;
#ifdef CONFIG_INOTIFY_USER
                struct inotify_group_private_data {
                        spinlock_t      idr_lock;
                        struct idr      idr;
                        u32             last_wd;
                        struct fasync_struct    *fa;    /* async notification */
                        struct user_struct      *user;
                } inotify_data;
#endif
        };
};

/*
 * A single event can be queued in multiple group->notification_lists.
 *
 * each group->notification_list will point to an event_holder which in turns points
 * to the actual event that needs to be sent to userspace.
 *
 * Seemed cheaper to create a refcnt'd event and a small holder for every group
 * than create a different event for every group
 *
 */
struct fsnotify_event_holder {
        struct fsnotify_event *event;
        struct list_head event_list;
};

/*
 * Inotify needs to tack data onto an event.  This struct lets us later find the
 * correct private data of the correct group.
 */
struct fsnotify_event_private_data {
        struct fsnotify_group *group;
        struct list_head event_list;
};

/*
 * all of the information about the original object we want to now send to
 * a group.  If you want to carry more info from the accessing task to the
 * listener this structure is where you need to be adding fields.
 */
struct fsnotify_event {
        /*
         * If we create an event we are also likely going to need a holder
         * to link to a group.  So embed one holder in the event.  Means only
         * one allocation for the common case where we only have one group
         */
        struct fsnotify_event_holder holder;
        spinlock_t lock;        /* protection for the associated event_holder and private_list */
        /* to_tell may ONLY be dereferenced during handle_event(). */
        struct inode *to_tell;  /* either the inode the event happened to or its parent */
        /*
         * depending on the event type we should have either a path or inode
         * We hold a reference on path, but NOT on inode.  Since we have the ref on
         * the path, it may be dereferenced at any point during this object's
         * lifetime.  That reference is dropped when this object's refcnt hits
         * 0.  If this event contains an inode instead of a path, the inode may
         * ONLY be used during handle_event().
         */
        union {
                struct path path;
                struct inode *inode;
        };
/* when calling fsnotify tell it if the data is a path or inode */
#define FSNOTIFY_EVENT_NONE     0
#define FSNOTIFY_EVENT_PATH     1
#define FSNOTIFY_EVENT_INODE    2
#define FSNOTIFY_EVENT_FILE     3
        int data_type;          /* which of the above union we have */
        atomic_t refcnt;        /* how many groups still are using/need to send this event */
        __u32 mask;             /* the type of access, bitwise OR for FS_* event types */

        u32 sync_cookie;        /* used to corrolate events, namely inotify mv events */
        char *file_name;
        size_t name_len;

        struct list_head private_data_list;     /* groups can store private data here */
};

/*
 * a mark is simply an entry attached to an in core inode which allows an
 * fsnotify listener to indicate they are either no longer interested in events
 * of a type matching mask or only interested in those events.
 *
 * these are flushed when an inode is evicted from core and may be flushed
 * when the inode is modified (as seen by fsnotify_access).  Some fsnotify users
 * (such as dnotify) will flush these when the open fd is closed and not at
 * inode eviction or modification.
 */
struct fsnotify_mark_entry {
        __u32 mask;                     /* mask this mark entry is for */
        /* we hold ref for each i_list and g_list.  also one ref for each 'thing'
         * in kernel that found and may be using this mark. */
        atomic_t refcnt;                /* active things looking at this mark */
        struct inode *inode;            /* inode this entry is associated with */
        struct fsnotify_group *group;   /* group this mark entry is for */
        struct hlist_node i_list;       /* list of mark_entries by inode->i_fsnotify_mark_entries */
        struct list_head g_list;        /* list of mark_entries by group->i_fsnotify_mark_entries */
        spinlock_t lock;                /* protect group, inode, and killme */
        struct list_head free_i_list;   /* tmp list used when freeing this mark */
        struct list_head free_g_list;   /* tmp list used when freeing this mark */
        void (*free_mark)(struct fsnotify_mark_entry *entry); /* called on final put+free */
};

#ifdef CONFIG_FSNOTIFY

/* called from the vfs helpers */

/* main fsnotify call to send events */
extern void fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is,
                     const char *name, u32 cookie);
extern void __fsnotify_parent(struct dentry *dentry, __u32 mask);
extern void __fsnotify_inode_delete(struct inode *inode);
extern u32 fsnotify_get_cookie(void);

static inline int fsnotify_inode_watches_children(struct inode *inode)
{
        /* FS_EVENT_ON_CHILD is set if the inode may care */
        if (!(inode->i_fsnotify_mask & FS_EVENT_ON_CHILD))
                return 0;
        /* this inode might care about child events, does it care about the
         * specific set of events that can happen on a child? */
        return inode->i_fsnotify_mask & FS_EVENTS_POSS_ON_CHILD;
}

/*
 * Update the dentry with a flag indicating the interest of its parent to receive
 * filesystem events when those events happens to this dentry->d_inode.
 */
static inline void __fsnotify_update_dcache_flags(struct dentry *dentry)
{
        struct dentry *parent;

        assert_spin_locked(&dcache_lock);
        assert_spin_locked(&dentry->d_lock);

        parent = dentry->d_parent;
        if (parent->d_inode && fsnotify_inode_watches_children(parent->d_inode))
                dentry->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED;
        else
                dentry->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
}

/*
 * fsnotify_d_instantiate - instantiate a dentry for inode
 * Called with dcache_lock held.
 */
static inline void __fsnotify_d_instantiate(struct dentry *dentry, struct inode *inode)
{
        if (!inode)
                return;

        assert_spin_locked(&dcache_lock);

        spin_lock(&dentry->d_lock);
        __fsnotify_update_dcache_flags(dentry);
        spin_unlock(&dentry->d_lock);
}

/* called from fsnotify listeners, such as fanotify or dnotify */

/* must call when a group changes its ->mask */
extern void fsnotify_recalc_global_mask(void);
/* get a reference to an existing or create a new group */
extern struct fsnotify_group *fsnotify_obtain_group(unsigned int group_num,
                                                    __u32 mask,
                                                    const struct fsnotify_ops *ops);
/* run all marks associated with this group and update group->mask */
extern void fsnotify_recalc_group_mask(struct fsnotify_group *group);
/* drop reference on a group from fsnotify_obtain_group */
extern void fsnotify_put_group(struct fsnotify_group *group);

/* take a reference to an event */
extern void fsnotify_get_event(struct fsnotify_event *event);
extern void fsnotify_put_event(struct fsnotify_event *event);
/* find private data previously attached to an event and unlink it */
extern struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnotify_group *group,
                                                                           struct fsnotify_event *event);

/* attach the event to the group notification queue */
extern int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
                                     struct fsnotify_event_private_data *priv);
/* true if the group notification queue is empty */
extern bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group);
/* return, but do not dequeue the first event on the notification queue */
extern struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group);
/* return AND dequeue the first event on the notification queue */
extern struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group);

/* functions used to manipulate the marks attached to inodes */

/* run all marks associated with an inode and update inode->i_fsnotify_mask */
extern void fsnotify_recalc_inode_mask(struct inode *inode);
extern void fsnotify_init_mark(struct fsnotify_mark_entry *entry, void (*free_mark)(struct fsnotify_mark_entry *entry));
/* find (and take a reference) to a mark associated with group and inode */
extern struct fsnotify_mark_entry *fsnotify_find_mark_entry(struct fsnotify_group *group, struct inode *inode);
/* attach the mark to both the group and the inode */
extern int fsnotify_add_mark(struct fsnotify_mark_entry *entry, struct fsnotify_group *group, struct inode *inode);
/* given a mark, flag it to be freed when all references are dropped */
extern void fsnotify_destroy_mark_by_entry(struct fsnotify_mark_entry *entry);
/* run all the marks in a group, and flag them to be freed */
extern void fsnotify_clear_marks_by_group(struct fsnotify_group *group);
extern void fsnotify_get_mark(struct fsnotify_mark_entry *entry);
extern void fsnotify_put_mark(struct fsnotify_mark_entry *entry);
extern void fsnotify_unmount_inodes(struct list_head *list);

/* put here because inotify does some weird stuff when destroying watches */
extern struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask,
                                                    void *data, int data_is, const char *name,
                                                    u32 cookie, gfp_t gfp);

#else

static inline void fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is,
                            const char *name, u32 cookie)
{}

static inline void __fsnotify_parent(struct dentry *dentry, __u32 mask)
{}

static inline void __fsnotify_inode_delete(struct inode *inode)
{}

static inline void __fsnotify_update_dcache_flags(struct dentry *dentry)
{}

static inline void __fsnotify_d_instantiate(struct dentry *dentry, struct inode *inode)
{}

static inline u32 fsnotify_get_cookie(void)
{
        return 0;
}

static inline void fsnotify_unmount_inodes(struct list_head *list)
{}

#endif  /* CONFIG_FSNOTIFY */

#endif  /* __KERNEL __ */

#endif  /* __LINUX_FSNOTIFY_BACKEND_H */