fsnotify_backend.h

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/*
 * Filesystem access notification for Linux
 *
 *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <[email protected]>
 */

#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 <linux/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_OPEN_PERM        0x00010000  /* open event in an permission hook */
#define FS_ACCESS_PERM      0x00020000  /* access event in a permissions hook */

#define FS_EXCL_UNLINK      0x04000000  /* do not send events if object is unlinked */
#define FS_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 | FS_OPEN_PERM | FS_ACCESS_PERM)

#define FS_MOVE         (FS_MOVED_FROM | FS_MOVED_TO)

#define ALL_FSNOTIFY_PERM_EVENTS (FS_OPEN_PERM | FS_ACCESS_PERM)

#define ALL_FSNOTIFY_EVENTS (FS_ACCESS | FS_MODIFY | FS_ATTRIB | \
                 FS_CLOSE_WRITE | FS_CLOSE_NOWRITE | FS_OPEN | \
                 FS_MOVED_FROM | FS_MOVED_TO | FS_CREATE | \
                 FS_DELETE | FS_DELETE_SELF | FS_MOVE_SELF | \
                 FS_UNMOUNT | FS_Q_OVERFLOW | FS_IN_IGNORED | \
                 FS_OPEN_PERM | FS_ACCESS_PERM | FS_EXCL_UNLINK | \
                 FS_ISDIR | FS_IN_ONESHOT | FS_DN_RENAME | \
                 FS_DN_MULTISHOT | FS_EVENT_ON_CHILD)

struct fsnotify_group;
struct fsnotify_event;
struct fsnotify_mark;
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,
                  struct fsnotify_mark *inode_mark,
                  struct fsnotify_mark *vfsmount_mark,
                  __u32 mask, void *data, int data_type);
    int (*handle_event)(struct fsnotify_group *group,
                struct fsnotify_mark *inode_mark,
                struct fsnotify_mark *vfsmount_mark,
                struct fsnotify_event *event);
    void (*free_group_priv)(struct fsnotify_group *group);
    void (*freeing_mark)(struct fsnotify_mark *mark, 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 {
    /*
     * 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 */

    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 */
    /*
     * Valid fsnotify group priorities.  Events are send in order from highest
     * priority to lowest priority.  We default to the lowest priority.
     */
    #define FS_PRIO_0   0 /* normal notifiers, no permissions */
    #define FS_PRIO_1   1 /* fanotify content based access control */
    #define FS_PRIO_2   2 /* fanotify pre-content access */
    unsigned int priority;

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

    /* 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
#ifdef CONFIG_FANOTIFY
        struct fanotify_group_private_data {
#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
            /* allows a group to block waiting for a userspace response */
            struct mutex access_mutex;
            struct list_head access_list;
            wait_queue_head_t access_waitq;
            atomic_t bypass_perm;
#endif /* CONFIG_FANOTIFY_ACCESS_PERMISSIONS */
            int f_flags;
            unsigned int max_marks;
            struct user_struct *user;
        } fanotify_data;
#endif /* CONFIG_FANOTIFY */
    };
};

/*
 * 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
    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 */
    const unsigned char *file_name;
    size_t name_len;
    struct pid *tgid;

#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
    __u32 response; /* userspace answer to question */
#endif /* CONFIG_FANOTIFY_ACCESS_PERMISSIONS */

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

/*
 * Inode specific fields in an fsnotify_mark
 */
struct fsnotify_inode_mark {
    struct inode *inode;        /* inode this mark is associated with */
    struct hlist_node i_list;   /* list of marks by inode->i_fsnotify_marks */
    struct list_head free_i_list;   /* tmp list used when freeing this mark */
};

/*
 * Mount point specific fields in an fsnotify_mark
 */
struct fsnotify_vfsmount_mark {
    struct vfsmount *mnt;       /* vfsmount this mark is associated with */
    struct hlist_node m_list;   /* list of marks by inode->i_fsnotify_marks */
    struct list_head free_m_list;   /* tmp list used when freeing this mark */
};

/*
 * a mark is simply an object 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 {
    __u32 mask;         /* mask this mark 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 fsnotify_group *group;   /* group this mark is for */
    struct list_head g_list;    /* list of marks by group->i_fsnotify_marks */
    spinlock_t lock;        /* protect group and inode */
    union {
        struct fsnotify_inode_mark i;
        struct fsnotify_vfsmount_mark m;
    };
    struct list_head free_g_list;   /* tmp list used when freeing this mark */
    __u32 ignored_mask;     /* events types to ignore */
#define FSNOTIFY_MARK_FLAG_INODE        0x01
#define FSNOTIFY_MARK_FLAG_VFSMOUNT     0x02
#define FSNOTIFY_MARK_FLAG_OBJECT_PINNED    0x04
#define FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY  0x08
#define FSNOTIFY_MARK_FLAG_ALIVE        0x10
    unsigned int flags;     /* vfsmount or inode mark? */
    struct list_head destroy_list;
    void (*free_mark)(struct fsnotify_mark *mark); /* called on final put+free */
};

#ifdef CONFIG_FSNOTIFY

/* called from the vfs helpers */

/* main fsnotify call to send events */
extern int fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is,
            const unsigned char *name, u32 cookie);
extern int __fsnotify_parent(struct path *path, struct dentry *dentry, __u32 mask);
extern void __fsnotify_inode_delete(struct inode *inode);
extern void __fsnotify_vfsmount_delete(struct vfsmount *mnt);
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(&dentry->d_lock);

    /*
     * Serialisation of setting PARENT_WATCHED on the dentries is provided
     * by d_lock. If inotify_inode_watched changes after we have taken
     * d_lock, the following __fsnotify_update_child_dentry_flags call will
     * find our entry, so it will spin until we complete here, and update
     * us with the new state.
     */
    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
 */
static inline void __fsnotify_d_instantiate(struct dentry *dentry, struct inode *inode)
{
    if (!inode)
        return;

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

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

/* get a reference to an existing or create a new group */
extern struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops);
/* drop reference on a group from fsnotify_alloc_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 struct fsnotify_event *fsnotify_add_notify_event(struct fsnotify_group *group,
                            struct fsnotify_event *event,
                            struct fsnotify_event_private_data *priv,
                            struct fsnotify_event *(*merge)(struct list_head *,
                                            struct fsnotify_event *));
/* 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 a vfsmount and update mnt->mnt_fsnotify_mask */
extern void fsnotify_recalc_vfsmount_mask(struct vfsmount *mnt);
/* 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 *mark, void (*free_mark)(struct fsnotify_mark *mark));
/* find (and take a reference) to a mark associated with group and inode */
extern struct fsnotify_mark *fsnotify_find_inode_mark(struct fsnotify_group *group, struct inode *inode);
/* find (and take a reference) to a mark associated with group and vfsmount */
extern struct fsnotify_mark *fsnotify_find_vfsmount_mark(struct fsnotify_group *group, struct vfsmount *mnt);
/* copy the values from old into new */
extern void fsnotify_duplicate_mark(struct fsnotify_mark *new, struct fsnotify_mark *old);
/* set the ignored_mask of a mark */
extern void fsnotify_set_mark_ignored_mask_locked(struct fsnotify_mark *mark, __u32 mask);
/* set the mask of a mark (might pin the object into memory */
extern void fsnotify_set_mark_mask_locked(struct fsnotify_mark *mark, __u32 mask);
/* attach the mark to both the group and the inode */
extern int fsnotify_add_mark(struct fsnotify_mark *mark, struct fsnotify_group *group,
                 struct inode *inode, struct vfsmount *mnt, int allow_dups);
/* given a mark, flag it to be freed when all references are dropped */
extern void fsnotify_destroy_mark(struct fsnotify_mark *mark);
/* run all the marks in a group, and clear all of the vfsmount marks */
extern void fsnotify_clear_vfsmount_marks_by_group(struct fsnotify_group *group);
/* run all the marks in a group, and clear all of the inode marks */
extern void fsnotify_clear_inode_marks_by_group(struct fsnotify_group *group);
/* run all the marks in a group, and clear all of the marks where mark->flags & flags is true*/
extern void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group, unsigned int flags);
/* 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 *mark);
extern void fsnotify_put_mark(struct fsnotify_mark *mark);
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 unsigned char *name,
                            u32 cookie, gfp_t gfp);

/* fanotify likes to change events after they are on lists... */
extern struct fsnotify_event *fsnotify_clone_event(struct fsnotify_event *old_event);
extern int fsnotify_replace_event(struct fsnotify_event_holder *old_holder,
                  struct fsnotify_event *new_event);

#else

static inline int fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is,
               const unsigned char *name, u32 cookie)
{
    return 0;
}

static inline int __fsnotify_parent(struct path *path, struct dentry *dentry, __u32 mask)
{
    return 0;
}

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

static inline void __fsnotify_vfsmount_delete(struct vfsmount *mnt)
{}

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 */