[PATCH] inotify (1/5): split kernel API from userspace support

The following series of patches introduces a kernel API for inotify,
making it possible for kernel modules to benefit from inotify's
mechanism for watching inodes.  With these patches, inotify will
maintain for each caller a list of watches (via an embedded struct
inotify_watch), where each inotify_watch is associated with a
corresponding struct inode.  The caller registers an event handler and
specifies for which filesystem events their event handler should be
called per inotify_watch.

Signed-off-by: Amy Griffis <amy.griffis@hp.com>
Acked-by: Robert Love <rml@novell.com>
Acked-by: John McCutchan <john@johnmccutchan.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 717 insertions, 0 deletions

diff --git a/fs/inotify_user.c b/fs/inotify_user.c
new file mode 100644
index 000000000000..845dc79a4e9c
--- /dev/null
+++ b/fs/inotify_user.c
@@ -0,0 +1,717 @@
+/*
+ * fs/inotify_user.c - inotify support for userspace
+ *
+ * Authors:
+ *      John McCutchan  <ttb@tentacle.dhs.org>
+ *      Robert Love     <rml@novell.com>
+ *
+ * Copyright (C) 2005 John McCutchan
+ * Copyright 2006 Hewlett-Packard Development Company, L.P.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2, or (at your option) any
+ * later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
+#include <linux/poll.h>
+#include <linux/init.h>
+#include <linux/list.h>
+#include <linux/inotify.h>
+#include <linux/syscalls.h>
+
+#include <asm/ioctls.h>
+
+static kmem_cache_t *watch_cachep __read_mostly;
+static kmem_cache_t *event_cachep __read_mostly;
+
+static struct vfsmount *inotify_mnt __read_mostly;
+
+/* these are configurable via /proc/sys/fs/inotify/ */
+int inotify_max_user_instances __read_mostly;
+int inotify_max_user_watches __read_mostly;
+int inotify_max_queued_events __read_mostly;
+
+/*
+ * Lock ordering:
+ *
+ * inotify_dev->up_mutex (ensures we don't re-add the same watch)
+ *      inode->inotify_mutex (protects inode's watch list)
+ *              inotify_handle->mutex (protects inotify_handle's watch list)
+ *                      inotify_dev->ev_mutex (protects device's event queue)
+ */
+
+/*
+ * Lifetimes of the main data structures:
+ *
+ * inotify_device: Lifetime is managed by reference count, from
+ * sys_inotify_init() until release.  Additional references can bump the count
+ * via get_inotify_dev() and drop the count via put_inotify_dev().
+ *
+ * inotify_user_watch: Lifetime is from create_watch() to the receipt of an
+ * IN_IGNORED event from inotify, or when using IN_ONESHOT, to receipt of the
+ * first event, or to inotify_destroy().
+ */
+
+/*
+ * struct inotify_device - represents an inotify instance
+ *
+ * This structure is protected by the mutex 'mutex'.
+ */
+struct inotify_device {
+        wait_queue_head_t       wq;             /* wait queue for i/o */
+        struct mutex            ev_mutex;       /* protects event queue */
+        struct mutex            up_mutex;       /* synchronizes watch updates */
+        struct list_head        events;         /* list of queued events */
+        atomic_t                count;          /* reference count */
+        struct user_struct      *user;          /* user who opened this dev */
+        struct inotify_handle   *ih;            /* inotify handle */
+        unsigned int            queue_size;     /* size of the queue (bytes) */
+        unsigned int            event_count;    /* number of pending events */
+        unsigned int            max_events;     /* maximum number of events */
+};
+
+/*
+ * struct inotify_kernel_event - An inotify event, originating from a watch and
+ * queued for user-space.  A list of these is attached to each instance of the
+ * device.  In read(), this list is walked and all events that can fit in the
+ * buffer are returned.
+ *
+ * Protected by dev->ev_mutex of the device in which we are queued.
+ */
+struct inotify_kernel_event {
+        struct inotify_event    event;  /* the user-space event */
+        struct list_head        list;   /* entry in inotify_device's list */
+        char                    *name;  /* filename, if any */
+};
+
+/*
+ * struct inotify_user_watch - our version of an inotify_watch, we add
+ * a reference to the associated inotify_device.
+ */
+struct inotify_user_watch {
+        struct inotify_device   *dev;   /* associated device */
+        struct inotify_watch    wdata;  /* inotify watch data */
+};
+
+#ifdef CONFIG_SYSCTL
+
+#include <linux/sysctl.h>
+
+static int zero;
+
+ctl_table inotify_table[] = {
+        {
+                .ctl_name       = INOTIFY_MAX_USER_INSTANCES,
+                .procname       = "max_user_instances",
+                .data           = &inotify_max_user_instances,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec_minmax,
+                .strategy       = &sysctl_intvec,
+                .extra1         = &zero,
+        },
+        {
+                .ctl_name       = INOTIFY_MAX_USER_WATCHES,
+                .procname       = "max_user_watches",
+                .data           = &inotify_max_user_watches,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec_minmax,
+                .strategy       = &sysctl_intvec,
+                .extra1         = &zero,
+        },
+        {
+                .ctl_name       = INOTIFY_MAX_QUEUED_EVENTS,
+                .procname       = "max_queued_events",
+                .data           = &inotify_max_queued_events,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec_minmax,
+                .strategy       = &sysctl_intvec,
+                .extra1         = &zero
+        },
+        { .ctl_name = 0 }
+};
+#endif /* CONFIG_SYSCTL */
+
+static inline void get_inotify_dev(struct inotify_device *dev)
+{
+        atomic_inc(&dev->count);
+}
+
+static inline void put_inotify_dev(struct inotify_device *dev)
+{
+        if (atomic_dec_and_test(&dev->count)) {
+                atomic_dec(&dev->user->inotify_devs);
+                free_uid(dev->user);
+                kfree(dev);
+        }
+}
+
+/*
+ * free_inotify_user_watch - cleans up the watch and its references
+ */
+static void free_inotify_user_watch(struct inotify_watch *w)
+{
+        struct inotify_user_watch *watch;
+        struct inotify_device *dev;
+
+        watch = container_of(w, struct inotify_user_watch, wdata);
+        dev = watch->dev;
+
+        atomic_dec(&dev->user->inotify_watches);
+        put_inotify_dev(dev);
+        kmem_cache_free(watch_cachep, watch);
+}
+
+/*
+ * kernel_event - create a new kernel event with the given parameters
+ *
+ * This function can sleep.
+ */
+static struct inotify_kernel_event * kernel_event(s32 wd, u32 mask, u32 cookie,
+                                                  const char *name)
+{
+        struct inotify_kernel_event *kevent;
+
+        kevent = kmem_cache_alloc(event_cachep, GFP_KERNEL);
+        if (unlikely(!kevent))
+                return NULL;
+
+        /* we hand this out to user-space, so zero it just in case */
+        memset(&kevent->event, 0, sizeof(struct inotify_event));
+
+        kevent->event.wd = wd;
+        kevent->event.mask = mask;
+        kevent->event.cookie = cookie;
+
+        INIT_LIST_HEAD(&kevent->list);
+
+        if (name) {
+                size_t len, rem, event_size = sizeof(struct inotify_event);
+
+                /*
+                 * We need to pad the filename so as to properly align an
+                 * array of inotify_event structures.  Because the structure is
+                 * small and the common case is a small filename, we just round
+                 * up to the next multiple of the structure's sizeof.  This is
+                 * simple and safe for all architectures.
+                 */
+                len = strlen(name) + 1;
+                rem = event_size - len;
+                if (len > event_size) {
+                        rem = event_size - (len % event_size);
+                        if (len % event_size == 0)
+                                rem = 0;
+                }
+
+                kevent->name = kmalloc(len + rem, GFP_KERNEL);
+                if (unlikely(!kevent->name)) {
+                        kmem_cache_free(event_cachep, kevent);
+                        return NULL;
+                }
+                memcpy(kevent->name, name, len);
+                if (rem)
+                        memset(kevent->name + len, 0, rem);
+                kevent->event.len = len + rem;
+        } else {
+                kevent->event.len = 0;
+                kevent->name = NULL;
+        }
+
+        return kevent;
+}
+
+/*
+ * inotify_dev_get_event - return the next event in the given dev's queue
+ *
+ * Caller must hold dev->ev_mutex.
+ */
+static inline struct inotify_kernel_event *
+inotify_dev_get_event(struct inotify_device *dev)
+{
+        return list_entry(dev->events.next, struct inotify_kernel_event, list);
+}
+
+/*
+ * inotify_dev_queue_event - event handler registered with core inotify, adds
+ * a new event to the given device
+ *
+ * Can sleep (calls kernel_event()).
+ */
+static void inotify_dev_queue_event(struct inotify_watch *w, u32 wd, u32 mask,
+                                    u32 cookie, const char *name)
+{
+        struct inotify_user_watch *watch;
+        struct inotify_device *dev;
+        struct inotify_kernel_event *kevent, *last;
+
+        watch = container_of(w, struct inotify_user_watch, wdata);
+        dev = watch->dev;
+
+        mutex_lock(&dev->ev_mutex);
+
+        /* we can safely put the watch as we don't reference it while
+         * generating the event
+         */
+        if (mask & IN_IGNORED || mask & IN_ONESHOT)
+                put_inotify_watch(w); /* final put */
+
+        /* coalescing: drop this event if it is a dupe of the previous */
+        last = inotify_dev_get_event(dev);
+        if (last && last->event.mask == mask && last->event.wd == wd &&
+                        last->event.cookie == cookie) {
+                const char *lastname = last->name;
+
+                if (!name && !lastname)
+                        goto out;
+                if (name && lastname && !strcmp(lastname, name))
+                        goto out;
+        }
+
+        /* the queue overflowed and we already sent the Q_OVERFLOW event */
+        if (unlikely(dev->event_count > dev->max_events))
+                goto out;
+
+        /* if the queue overflows, we need to notify user space */
+        if (unlikely(dev->event_count == dev->max_events))
+                kevent = kernel_event(-1, IN_Q_OVERFLOW, cookie, NULL);
+        else
+                kevent = kernel_event(wd, mask, cookie, name);
+
+        if (unlikely(!kevent))
+                goto out;
+
+        /* queue the event and wake up anyone waiting */
+        dev->event_count++;
+        dev->queue_size += sizeof(struct inotify_event) + kevent->event.len;
+        list_add_tail(&kevent->list, &dev->events);
+        wake_up_interruptible(&dev->wq);
+
+out:
+        mutex_unlock(&dev->ev_mutex);
+}
+
+/*
+ * remove_kevent - cleans up and ultimately frees the given kevent
+ *
+ * Caller must hold dev->ev_mutex.
+ */
+static void remove_kevent(struct inotify_device *dev,
+                          struct inotify_kernel_event *kevent)
+{
+        list_del(&kevent->list);
+
+        dev->event_count--;
+        dev->queue_size -= sizeof(struct inotify_event) + kevent->event.len;
+
+        kfree(kevent->name);
+        kmem_cache_free(event_cachep, kevent);
+}
+
+/*
+ * inotify_dev_event_dequeue - destroy an event on the given device
+ *
+ * Caller must hold dev->ev_mutex.
+ */
+static void inotify_dev_event_dequeue(struct inotify_device *dev)
+{
+        if (!list_empty(&dev->events)) {
+                struct inotify_kernel_event *kevent;
+                kevent = inotify_dev_get_event(dev);
+                remove_kevent(dev, kevent);
+        }
+}
+
+/*
+ * find_inode - resolve a user-given path to a specific inode and return a nd
+ */
+static int find_inode(const char __user *dirname, struct nameidata *nd,
+                      unsigned flags)
+{
+        int error;
+
+        error = __user_walk(dirname, flags, nd);
+        if (error)
+                return error;
+        /* you can only watch an inode if you have read permissions on it */
+        error = vfs_permission(nd, MAY_READ);
+        if (error)
+                path_release(nd);
+        return error;
+}
+
+/*
+ * create_watch - creates a watch on the given device.
+ *
+ * Callers must hold dev->up_mutex.
+ */
+static int create_watch(struct inotify_device *dev, struct inode *inode,
+                        u32 mask)
+{
+        struct inotify_user_watch *watch;
+        int ret;
+
+        if (atomic_read(&dev->user->inotify_watches) >=
+                        inotify_max_user_watches)
+                return -ENOSPC;
+
+        watch = kmem_cache_alloc(watch_cachep, GFP_KERNEL);
+        if (unlikely(!watch))
+                return -ENOMEM;
+
+        /* save a reference to device and bump the count to make it official */
+        get_inotify_dev(dev);
+        watch->dev = dev;
+
+        atomic_inc(&dev->user->inotify_watches);
+
+        ret = inotify_add_watch(dev->ih, &watch->wdata, inode, mask);
+        if (ret < 0)
+                free_inotify_user_watch(&watch->wdata);
+
+        return ret;
+}
+
+/* Device Interface */
+
+static unsigned int inotify_poll(struct file *file, poll_table *wait)
+{
+        struct inotify_device *dev = file->private_data;
+        int ret = 0;
+
+        poll_wait(file, &dev->wq, wait);
+        mutex_lock(&dev->ev_mutex);
+        if (!list_empty(&dev->events))
+                ret = POLLIN | POLLRDNORM;
+        mutex_unlock(&dev->ev_mutex);
+
+        return ret;
+}
+
+static ssize_t inotify_read(struct file *file, char __user *buf,
+                            size_t count, loff_t *pos)
+{
+        size_t event_size = sizeof (struct inotify_event);
+        struct inotify_device *dev;
+        char __user *start;
+        int ret;
+        DEFINE_WAIT(wait);
+
+        start = buf;
+        dev = file->private_data;
+
+        while (1) {
+                int events;
+
+                prepare_to_wait(&dev->wq, &wait, TASK_INTERRUPTIBLE);
+
+                mutex_lock(&dev->ev_mutex);
+                events = !list_empty(&dev->events);
+                mutex_unlock(&dev->ev_mutex);
+                if (events) {
+                        ret = 0;
+                        break;
+                }
+
+                if (file->f_flags & O_NONBLOCK) {
+                        ret = -EAGAIN;
+                        break;
+                }
+
+                if (signal_pending(current)) {
+                        ret = -EINTR;
+                        break;
+                }
+
+                schedule();
+        }
+
+        finish_wait(&dev->wq, &wait);
+        if (ret)
+                return ret;
+
+        mutex_lock(&dev->ev_mutex);
+        while (1) {
+                struct inotify_kernel_event *kevent;
+
+                ret = buf - start;
+                if (list_empty(&dev->events))
+                        break;
+
+                kevent = inotify_dev_get_event(dev);
+                if (event_size + kevent->event.len > count)
+                        break;
+
+                if (copy_to_user(buf, &kevent->event, event_size)) {
+                        ret = -EFAULT;
+                        break;
+                }
+                buf += event_size;
+                count -= event_size;
+
+                if (kevent->name) {
+                        if (copy_to_user(buf, kevent->name, kevent->event.len)){
+                                ret = -EFAULT;
+                                break;
+                        }
+                        buf += kevent->event.len;
+                        count -= kevent->event.len;
+                }
+
+                remove_kevent(dev, kevent);
+        }
+        mutex_unlock(&dev->ev_mutex);
+
+        return ret;
+}
+
+static int inotify_release(struct inode *ignored, struct file *file)
+{
+        struct inotify_device *dev = file->private_data;
+
+        inotify_destroy(dev->ih);
+
+        /* destroy all of the events on this device */
+        mutex_lock(&dev->ev_mutex);
+        while (!list_empty(&dev->events))
+                inotify_dev_event_dequeue(dev);
+        mutex_unlock(&dev->ev_mutex);
+
+        /* free this device: the put matching the get in inotify_init() */
+        put_inotify_dev(dev);
+
+        return 0;
+}
+
+static long inotify_ioctl(struct file *file, unsigned int cmd,
+                          unsigned long arg)
+{
+        struct inotify_device *dev;
+        void __user *p;
+        int ret = -ENOTTY;
+
+        dev = file->private_data;
+        p = (void __user *) arg;
+
+        switch (cmd) {
+        case FIONREAD:
+                ret = put_user(dev->queue_size, (int __user *) p);
+                break;
+        }
+
+        return ret;
+}
+
+static const struct file_operations inotify_fops = {
+        .poll           = inotify_poll,
+        .read           = inotify_read,
+        .release        = inotify_release,
+        .unlocked_ioctl = inotify_ioctl,
+        .compat_ioctl   = inotify_ioctl,
+};
+
+static const struct inotify_operations inotify_user_ops = {
+        .handle_event   = inotify_dev_queue_event,
+        .destroy_watch  = free_inotify_user_watch,
+};
+
+asmlinkage long sys_inotify_init(void)
+{
+        struct inotify_device *dev;
+        struct inotify_handle *ih;
+        struct user_struct *user;
+        struct file *filp;
+        int fd, ret;
+
+        fd = get_unused_fd();
+        if (fd < 0)
+                return fd;
+
+        filp = get_empty_filp();
+        if (!filp) {
+                ret = -ENFILE;
+                goto out_put_fd;
+        }
+
+        user = get_uid(current->user);
+        if (unlikely(atomic_read(&user->inotify_devs) >=
+                        inotify_max_user_instances)) {
+                ret = -EMFILE;
+                goto out_free_uid;
+        }
+
+        dev = kmalloc(sizeof(struct inotify_device), GFP_KERNEL);
+        if (unlikely(!dev)) {
+                ret = -ENOMEM;
+                goto out_free_uid;
+        }
+
+        ih = inotify_init(&inotify_user_ops);
+        if (unlikely(IS_ERR(ih))) {
+                ret = PTR_ERR(ih);
+                goto out_free_dev;
+        }
+        dev->ih = ih;
+
+        filp->f_op = &inotify_fops;
+        filp->f_vfsmnt = mntget(inotify_mnt);
+        filp->f_dentry = dget(inotify_mnt->mnt_root);
+        filp->f_mapping = filp->f_dentry->d_inode->i_mapping;
+        filp->f_mode = FMODE_READ;
+        filp->f_flags = O_RDONLY;
+        filp->private_data = dev;
+
+        INIT_LIST_HEAD(&dev->events);
+        init_waitqueue_head(&dev->wq);
+        mutex_init(&dev->ev_mutex);
+        mutex_init(&dev->up_mutex);
+        dev->event_count = 0;
+        dev->queue_size = 0;
+        dev->max_events = inotify_max_queued_events;
+        dev->user = user;
+        atomic_set(&dev->count, 0);
+
+        get_inotify_dev(dev);
+        atomic_inc(&user->inotify_devs);
+        fd_install(fd, filp);
+
+        return fd;
+out_free_dev:
+        kfree(dev);
+out_free_uid:
+        free_uid(user);
+        put_filp(filp);
+out_put_fd:
+        put_unused_fd(fd);
+        return ret;
+}
+
+asmlinkage long sys_inotify_add_watch(int fd, const char __user *path, u32 mask)
+{
+        struct inode *inode;
+        struct inotify_device *dev;
+        struct nameidata nd;
+        struct file *filp;
+        int ret, fput_needed;
+        unsigned flags = 0;
+
+        filp = fget_light(fd, &fput_needed);
+        if (unlikely(!filp))
+                return -EBADF;
+
+        /* verify that this is indeed an inotify instance */
+        if (unlikely(filp->f_op != &inotify_fops)) {
+                ret = -EINVAL;
+                goto fput_and_out;
+        }
+
+        if (!(mask & IN_DONT_FOLLOW))
+                flags |= LOOKUP_FOLLOW;
+        if (mask & IN_ONLYDIR)
+                flags |= LOOKUP_DIRECTORY;
+
+        ret = find_inode(path, &nd, flags);
+        if (unlikely(ret))
+                goto fput_and_out;
+
+        /* inode held in place by reference to nd; dev by fget on fd */
+        inode = nd.dentry->d_inode;
+        dev = filp->private_data;
+
+        mutex_lock(&dev->up_mutex);
+        ret = inotify_find_update_watch(dev->ih, inode, mask);
+        if (ret == -ENOENT)
+                ret = create_watch(dev, inode, mask);
+        mutex_unlock(&dev->up_mutex);
+
+        path_release(&nd);
+fput_and_out:
+        fput_light(filp, fput_needed);
+        return ret;
+}
+
+asmlinkage long sys_inotify_rm_watch(int fd, u32 wd)
+{
+        struct file *filp;
+        struct inotify_device *dev;
+        int ret, fput_needed;
+
+        filp = fget_light(fd, &fput_needed);
+        if (unlikely(!filp))
+                return -EBADF;
+
+        /* verify that this is indeed an inotify instance */
+        if (unlikely(filp->f_op != &inotify_fops)) {
+                ret = -EINVAL;
+                goto out;
+        }
+
+        dev = filp->private_data;
+
+        /* we free our watch data when we get IN_IGNORED */
+        ret = inotify_rm_wd(dev->ih, wd);
+
+out:
+        fput_light(filp, fput_needed);
+        return ret;
+}
+
+static struct super_block *
+inotify_get_sb(struct file_system_type *fs_type, int flags,
+               const char *dev_name, void *data)
+{
+    return get_sb_pseudo(fs_type, "inotify", NULL, 0xBAD1DEA);
+}
+
+static struct file_system_type inotify_fs_type = {
+    .name           = "inotifyfs",
+    .get_sb         = inotify_get_sb,
+    .kill_sb        = kill_anon_super,
+};
+
+/*
+ * inotify_user_setup - Our initialization function.  Note that we cannnot return
+ * error because we have compiled-in VFS hooks.  So an (unlikely) failure here
+ * must result in panic().
+ */
+static int __init inotify_user_setup(void)
+{
+        int ret;
+
+        ret = register_filesystem(&inotify_fs_type);
+        if (unlikely(ret))
+                panic("inotify: register_filesystem returned %d!\n", ret);
+
+        inotify_mnt = kern_mount(&inotify_fs_type);
+        if (IS_ERR(inotify_mnt))
+                panic("inotify: kern_mount ret %ld!\n", PTR_ERR(inotify_mnt));
+
+        inotify_max_queued_events = 16384;
+        inotify_max_user_instances = 128;
+        inotify_max_user_watches = 8192;
+
+        watch_cachep = kmem_cache_create("inotify_watch_cache",
+                                         sizeof(struct inotify_user_watch),
+                                         0, SLAB_PANIC, NULL, NULL);
+        event_cachep = kmem_cache_create("inotify_event_cache",
+                                         sizeof(struct inotify_kernel_event),
+                                         0, SLAB_PANIC, NULL, NULL);
+
+        return 0;
+}
+
+module_init(inotify_user_setup);