AFS: implement file locking

Implement file locking for AFS.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 558 insertions, 0 deletions

diff --git a/fs/afs/flock.c b/fs/afs/flock.c
new file mode 100644
index 000000000000..8f07f8d1bfa9
--- /dev/null
+++ b/fs/afs/flock.c
@@ -0,0 +1,558 @@
+/* AFS file locking support
+ *
+ * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * 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 of the License, or (at your option) any later version.
+ */
+
+#include <linux/smp_lock.h>
+#include "internal.h"
+
+#define AFS_LOCK_GRANTED        0
+#define AFS_LOCK_PENDING        1
+
+static void afs_fl_copy_lock(struct file_lock *new, struct file_lock *fl);
+static void afs_fl_release_private(struct file_lock *fl);
+
+static struct workqueue_struct *afs_lock_manager;
+
+static struct file_lock_operations afs_lock_ops = {
+        .fl_copy_lock           = afs_fl_copy_lock,
+        .fl_release_private     = afs_fl_release_private,
+};
+
+/*
+ * initialise the lock manager thread if it isn't already running
+ */
+static int afs_init_lock_manager(void)
+{
+        if (!afs_lock_manager) {
+                afs_lock_manager = create_singlethread_workqueue("kafs_lockd");
+                if (!afs_lock_manager)
+                        return -ENOMEM;
+        }
+        return 0;
+}
+
+/*
+ * destroy the lock manager thread if it's running
+ */
+void __exit afs_kill_lock_manager(void)
+{
+        if (afs_lock_manager)
+                destroy_workqueue(afs_lock_manager);
+}
+
+/*
+ * if the callback is broken on this vnode, then the lock may now be available
+ */
+void afs_lock_may_be_available(struct afs_vnode *vnode)
+{
+        _enter("{%x:%u}", vnode->fid.vid, vnode->fid.vnode);
+
+        queue_delayed_work(afs_lock_manager, &vnode->lock_work, 0);
+}
+
+/*
+ * the lock will time out in 5 minutes unless we extend it, so schedule
+ * extension in a bit less than that time
+ */
+static void afs_schedule_lock_extension(struct afs_vnode *vnode)
+{
+        queue_delayed_work(afs_lock_manager, &vnode->lock_work,
+                           AFS_LOCKWAIT * HZ / 2);
+}
+
+/*
+ * do work for a lock, including:
+ * - probing for a lock we're waiting on but didn't get immediately
+ * - extending a lock that's close to timing out
+ */
+void afs_lock_work(struct work_struct *work)
+{
+        struct afs_vnode *vnode =
+                container_of(work, struct afs_vnode, lock_work.work);
+        struct file_lock *fl;
+        afs_lock_type_t type;
+        struct key *key;
+        int ret;
+
+        _enter("{%x:%u}", vnode->fid.vid, vnode->fid.vnode);
+
+        spin_lock(&vnode->lock);
+
+        if (test_bit(AFS_VNODE_UNLOCKING, &vnode->flags)) {
+                _debug("unlock");
+                spin_unlock(&vnode->lock);
+
+                /* attempt to release the server lock; if it fails, we just
+                 * wait 5 minutes and it'll time out anyway */
+                ret = afs_vnode_release_lock(vnode, vnode->unlock_key);
+                if (ret < 0)
+                        printk(KERN_WARNING "AFS:"
+                               " Failed to release lock on {%x:%x} error %d\n",
+                               vnode->fid.vid, vnode->fid.vnode, ret);
+
+                spin_lock(&vnode->lock);
+                key_put(vnode->unlock_key);
+                vnode->unlock_key = NULL;
+                clear_bit(AFS_VNODE_UNLOCKING, &vnode->flags);
+        }
+
+        /* if we've got a lock, then it must be time to extend that lock as AFS
+         * locks time out after 5 minutes */
+        if (!list_empty(&vnode->granted_locks)) {
+                _debug("extend");
+
+                if (test_and_set_bit(AFS_VNODE_LOCKING, &vnode->flags))
+                        BUG();
+                fl = list_entry(vnode->granted_locks.next,
+                                struct file_lock, fl_u.afs.link);
+                key = key_get(fl->fl_file->private_data);
+                spin_unlock(&vnode->lock);
+
+                ret = afs_vnode_extend_lock(vnode, key);
+                clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
+                key_put(key);
+                switch (ret) {
+                case 0:
+                        afs_schedule_lock_extension(vnode);
+                        break;
+                default:
+                        /* ummm... we failed to extend the lock - retry
+                         * extension shortly */
+                        printk(KERN_WARNING "AFS:"
+                               " Failed to extend lock on {%x:%x} error %d\n",
+                               vnode->fid.vid, vnode->fid.vnode, ret);
+                        queue_delayed_work(afs_lock_manager, &vnode->lock_work,
+                                           HZ * 10);
+                        break;
+                }
+                _leave(" [extend]");
+                return;
+        }
+
+        /* if we don't have a granted lock, then we must've been called back by
+         * the server, and so if might be possible to get a lock we're
+         * currently waiting for */
+        if (!list_empty(&vnode->pending_locks)) {
+                _debug("get");
+
+                if (test_and_set_bit(AFS_VNODE_LOCKING, &vnode->flags))
+                        BUG();
+                fl = list_entry(vnode->pending_locks.next,
+                                struct file_lock, fl_u.afs.link);
+                key = key_get(fl->fl_file->private_data);
+                type = (fl->fl_type == F_RDLCK) ?
+                        AFS_LOCK_READ : AFS_LOCK_WRITE;
+                spin_unlock(&vnode->lock);
+
+                ret = afs_vnode_set_lock(vnode, key, type);
+                clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
+                switch (ret) {
+                case -EWOULDBLOCK:
+                        _debug("blocked");
+                        break;
+                case 0:
+                        _debug("acquired");
+                        if (type == AFS_LOCK_READ)
+                                set_bit(AFS_VNODE_READLOCKED, &vnode->flags);
+                        else
+                                set_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
+                        ret = AFS_LOCK_GRANTED;
+                default:
+                        spin_lock(&vnode->lock);
+                        /* the pending lock may have been withdrawn due to a
+                         * signal */
+                        if (list_entry(vnode->pending_locks.next,
+                                       struct file_lock, fl_u.afs.link) == fl) {
+                                fl->fl_u.afs.state = ret;
+                                if (ret == AFS_LOCK_GRANTED)
+                                        list_move_tail(&fl->fl_u.afs.link,
+                                                       &vnode->granted_locks);
+                                else
+                                        list_del_init(&fl->fl_u.afs.link);
+                                wake_up(&fl->fl_wait);
+                                spin_unlock(&vnode->lock);
+                        } else {
+                                _debug("withdrawn");
+                                clear_bit(AFS_VNODE_READLOCKED, &vnode->flags);
+                                clear_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
+                                spin_unlock(&vnode->lock);
+                                afs_vnode_release_lock(vnode, key);
+                                if (!list_empty(&vnode->pending_locks))
+                                        afs_lock_may_be_available(vnode);
+                        }
+                        break;
+                }
+                key_put(key);
+                _leave(" [pend]");
+                return;
+        }
+
+        /* looks like the lock request was withdrawn on a signal */
+        spin_unlock(&vnode->lock);
+        _leave(" [no locks]");
+}
+
+/*
+ * pass responsibility for the unlocking of a vnode on the server to the
+ * manager thread, lest a pending signal in the calling thread interrupt
+ * AF_RXRPC
+ * - the caller must hold the vnode lock
+ */
+static void afs_defer_unlock(struct afs_vnode *vnode, struct key *key)
+{
+        cancel_delayed_work(&vnode->lock_work);
+        if (!test_and_clear_bit(AFS_VNODE_READLOCKED, &vnode->flags) &&
+            !test_and_clear_bit(AFS_VNODE_WRITELOCKED, &vnode->flags))
+                BUG();
+        if (test_and_set_bit(AFS_VNODE_UNLOCKING, &vnode->flags))
+                BUG();
+        vnode->unlock_key = key_get(key);
+        afs_lock_may_be_available(vnode);
+}
+
+/*
+ * request a lock on a file on the server
+ */
+static int afs_do_setlk(struct file *file, struct file_lock *fl)
+{
+        struct afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
+        afs_lock_type_t type;
+        struct key *key = file->private_data;
+        int ret;
+
+        _enter("{%x:%u},%u", vnode->fid.vid, vnode->fid.vnode, fl->fl_type);
+
+        /* only whole-file locks are supported */
+        if (fl->fl_start != 0 || fl->fl_end != OFFSET_MAX)
+                return -EINVAL;
+
+        ret = afs_init_lock_manager();
+        if (ret < 0)
+                return ret;
+
+        fl->fl_ops = &afs_lock_ops;
+        INIT_LIST_HEAD(&fl->fl_u.afs.link);
+        fl->fl_u.afs.state = AFS_LOCK_PENDING;
+
+        type = (fl->fl_type == F_RDLCK) ? AFS_LOCK_READ : AFS_LOCK_WRITE;
+
+        lock_kernel();
+
+        /* make sure we've got a callback on this file and that our view of the
+         * data version is up to date */
+        ret = afs_vnode_fetch_status(vnode, NULL, key);
+        if (ret < 0)
+                goto error;
+
+        if (vnode->status.lock_count != 0 && !(fl->fl_flags & FL_SLEEP)) {
+                ret = -EAGAIN;
+                goto error;
+        }
+
+        spin_lock(&vnode->lock);
+
+        if (list_empty(&vnode->pending_locks)) {
+                /* if there's no-one else with a lock on this vnode, then we
+                 * need to ask the server for a lock */
+                if (list_empty(&vnode->granted_locks)) {
+                        _debug("not locked");
+                        ASSERTCMP(vnode->flags &
+                                  ((1 << AFS_VNODE_LOCKING) |
+                                   (1 << AFS_VNODE_READLOCKED) |
+                                   (1 << AFS_VNODE_WRITELOCKED)), ==, 0);
+                        list_add_tail(&fl->fl_u.afs.link, &vnode->pending_locks);
+                        set_bit(AFS_VNODE_LOCKING, &vnode->flags);
+                        spin_unlock(&vnode->lock);
+
+                        ret = afs_vnode_set_lock(vnode, key, type);
+                        clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
+                        switch (ret) {
+                        case 0:
+                                goto acquired_server_lock;
+                        case -EWOULDBLOCK:
+                                spin_lock(&vnode->lock);
+                                ASSERT(list_empty(&vnode->granted_locks));
+                                ASSERTCMP(vnode->pending_locks.next, ==,
+                                          &fl->fl_u.afs.link);
+                                goto wait;
+                        default:
+                                spin_lock(&vnode->lock);
+                                list_del_init(&fl->fl_u.afs.link);
+                                spin_unlock(&vnode->lock);
+                                goto error;
+                        }
+                }
+
+                /* if we've already got a readlock on the server and no waiting
+                 * writelocks, then we might be able to instantly grant another
+                 * readlock */
+                if (type == AFS_LOCK_READ &&
+                    vnode->flags & (1 << AFS_VNODE_READLOCKED)) {
+                        _debug("instant readlock");
+                        ASSERTCMP(vnode->flags &
+                                  ((1 << AFS_VNODE_LOCKING) |
+                                   (1 << AFS_VNODE_WRITELOCKED)), ==, 0);
+                        ASSERT(!list_empty(&vnode->granted_locks));
+                        goto sharing_existing_lock;
+                }
+        }
+
+        /* otherwise, we need to wait for a local lock to become available */
+        _debug("wait local");
+        list_add_tail(&fl->fl_u.afs.link, &vnode->pending_locks);
+wait:
+        if (!(fl->fl_flags & FL_SLEEP)) {
+                _debug("noblock");
+                ret = -EAGAIN;
+                goto abort_attempt;
+        }
+        spin_unlock(&vnode->lock);
+
+        /* now we need to sleep and wait for the lock manager thread to get the
+         * lock from the server */
+        _debug("sleep");
+        ret = wait_event_interruptible(fl->fl_wait,
+                                       fl->fl_u.afs.state <= AFS_LOCK_GRANTED);
+        if (fl->fl_u.afs.state <= AFS_LOCK_GRANTED) {
+                ret = fl->fl_u.afs.state;
+                if (ret < 0)
+                        goto error;
+                spin_lock(&vnode->lock);
+                goto given_lock;
+        }
+
+        /* we were interrupted, but someone may still be in the throes of
+         * giving us the lock */
+        _debug("intr");
+        ASSERTCMP(ret, ==, -ERESTARTSYS);
+
+        spin_lock(&vnode->lock);
+        if (fl->fl_u.afs.state <= AFS_LOCK_GRANTED) {
+                ret = fl->fl_u.afs.state;
+                if (ret < 0) {
+                        spin_unlock(&vnode->lock);
+                        goto error;
+                }
+                goto given_lock;
+        }
+
+abort_attempt:
+        /* we aren't going to get the lock, either because we're unwilling to
+         * wait, or because some signal happened */
+        _debug("abort");
+        if (list_empty(&vnode->granted_locks) &&
+            vnode->pending_locks.next == &fl->fl_u.afs.link) {
+                if (vnode->pending_locks.prev != &fl->fl_u.afs.link) {
+                        /* kick the next pending lock into having a go */
+                        list_del_init(&fl->fl_u.afs.link);
+                        afs_lock_may_be_available(vnode);
+                }
+        } else {
+                list_del_init(&fl->fl_u.afs.link);
+        }
+        spin_unlock(&vnode->lock);
+        goto error;
+
+acquired_server_lock:
+        /* we've acquired a server lock, but it needs to be renewed after 5
+         * mins */
+        spin_lock(&vnode->lock);
+        afs_schedule_lock_extension(vnode);
+        if (type == AFS_LOCK_READ)
+                set_bit(AFS_VNODE_READLOCKED, &vnode->flags);
+        else
+                set_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
+sharing_existing_lock:
+        /* the lock has been granted as far as we're concerned... */
+        fl->fl_u.afs.state = AFS_LOCK_GRANTED;
+        list_move_tail(&fl->fl_u.afs.link, &vnode->granted_locks);
+given_lock:
+        /* ... but we do still need to get the VFS's blessing */
+        ASSERT(!(vnode->flags & (1 << AFS_VNODE_LOCKING)));
+        ASSERT((vnode->flags & ((1 << AFS_VNODE_READLOCKED) |
+                                (1 << AFS_VNODE_WRITELOCKED))) != 0);
+        ret = posix_lock_file(file, fl, NULL);
+        if (ret < 0)
+                goto vfs_rejected_lock;
+        spin_unlock(&vnode->lock);
+
+        /* again, make sure we've got a callback on this file and, again, make
+         * sure that our view of the data version is up to date (we ignore
+         * errors incurred here and deal with the consequences elsewhere) */
+        afs_vnode_fetch_status(vnode, NULL, key);
+
+error:
+        unlock_kernel();
+        _leave(" = %d", ret);
+        return ret;
+
+vfs_rejected_lock:
+        /* the VFS rejected the lock we just obtained, so we have to discard
+         * what we just got */
+        _debug("vfs refused %d", ret);
+        list_del_init(&fl->fl_u.afs.link);
+        if (list_empty(&vnode->granted_locks))
+                afs_defer_unlock(vnode, key);
+        spin_unlock(&vnode->lock);
+        goto abort_attempt;
+}
+
+/*
+ * unlock on a file on the server
+ */
+static int afs_do_unlk(struct file *file, struct file_lock *fl)
+{
+        struct afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
+        struct key *key = file->private_data;
+        int ret;
+
+        _enter("{%x:%u},%u", vnode->fid.vid, vnode->fid.vnode, fl->fl_type);
+
+        /* only whole-file unlocks are supported */
+        if (fl->fl_start != 0 || fl->fl_end != OFFSET_MAX)
+                return -EINVAL;
+
+        fl->fl_ops = &afs_lock_ops;
+        INIT_LIST_HEAD(&fl->fl_u.afs.link);
+        fl->fl_u.afs.state = AFS_LOCK_PENDING;
+
+        spin_lock(&vnode->lock);
+        ret = posix_lock_file(file, fl, NULL);
+        if (ret < 0) {
+                spin_unlock(&vnode->lock);
+                _leave(" = %d [vfs]", ret);
+                return ret;
+        }
+
+        /* discard the server lock only if all granted locks are gone */
+        if (list_empty(&vnode->granted_locks))
+                afs_defer_unlock(vnode, key);
+        spin_unlock(&vnode->lock);
+        _leave(" = 0");
+        return 0;
+}
+
+/*
+ * return information about a lock we currently hold, if indeed we hold one
+ */
+static int afs_do_getlk(struct file *file, struct file_lock *fl)
+{
+        struct afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
+        struct key *key = file->private_data;
+        int ret, lock_count;
+
+        _enter("");
+
+        fl->fl_type = F_UNLCK;
+
+        mutex_lock(&vnode->vfs_inode.i_mutex);
+
+        /* check local lock records first */
+        ret = 0;
+        if (posix_test_lock(file, fl) == 0) {
+                /* no local locks; consult the server */
+                ret = afs_vnode_fetch_status(vnode, NULL, key);
+                if (ret < 0)
+                        goto error;
+                lock_count = vnode->status.lock_count;
+                if (lock_count) {
+                        if (lock_count > 0)
+                                fl->fl_type = F_RDLCK;
+                        else
+                                fl->fl_type = F_WRLCK;
+                        fl->fl_start = 0;
+                        fl->fl_end = OFFSET_MAX;
+                }
+        }
+
+error:
+        mutex_unlock(&vnode->vfs_inode.i_mutex);
+        _leave(" = %d [%hd]", ret, fl->fl_type);
+        return ret;
+}
+
+/*
+ * manage POSIX locks on a file
+ */
+int afs_lock(struct file *file, int cmd, struct file_lock *fl)
+{
+        struct afs_vnode *vnode = AFS_FS_I(file->f_dentry->d_inode);
+
+        _enter("{%x:%u},%d,{t=%x,fl=%x,r=%Ld:%Ld}",
+               vnode->fid.vid, vnode->fid.vnode, cmd,
+               fl->fl_type, fl->fl_flags,
+               (long long) fl->fl_start, (long long) fl->fl_end);
+
+        /* AFS doesn't support mandatory locks */
+        if ((vnode->vfs_inode.i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
+            fl->fl_type != F_UNLCK)
+                return -ENOLCK;
+
+        if (IS_GETLK(cmd))
+                return afs_do_getlk(file, fl);
+        if (fl->fl_type == F_UNLCK)
+                return afs_do_unlk(file, fl);
+        return afs_do_setlk(file, fl);
+}
+
+/*
+ * manage FLOCK locks on a file
+ */
+int afs_flock(struct file *file, int cmd, struct file_lock *fl)
+{
+        struct afs_vnode *vnode = AFS_FS_I(file->f_dentry->d_inode);
+
+        _enter("{%x:%u},%d,{t=%x,fl=%x}",
+               vnode->fid.vid, vnode->fid.vnode, cmd,
+               fl->fl_type, fl->fl_flags);
+
+        /*
+         * No BSD flocks over NFS allowed.
+         * Note: we could try to fake a POSIX lock request here by
+         * using ((u32) filp | 0x80000000) or some such as the pid.
+         * Not sure whether that would be unique, though, or whether
+         * that would break in other places.
+         */
+        if (!(fl->fl_flags & FL_FLOCK))
+                return -ENOLCK;
+
+        /* we're simulating flock() locks using posix locks on the server */
+        fl->fl_owner = (fl_owner_t) file;
+        fl->fl_start = 0;
+        fl->fl_end = OFFSET_MAX;
+
+        if (fl->fl_type == F_UNLCK)
+                return afs_do_unlk(file, fl);
+        return afs_do_setlk(file, fl);
+}
+
+/*
+ * the POSIX lock management core VFS code copies the lock record and adds the
+ * copy into its own list, so we need to add that copy to the vnode's lock
+ * queue in the same place as the original (which will be deleted shortly
+ * after)
+ */
+static void afs_fl_copy_lock(struct file_lock *new, struct file_lock *fl)
+{
+        _enter("");
+
+        list_add(&new->fl_u.afs.link, &fl->fl_u.afs.link);
+}
+
+/*
+ * need to remove this lock from the vnode queue when it's removed from the
+ * VFS's list
+ */
+static void afs_fl_release_private(struct file_lock *fl)
+{
+        _enter("");
+
+        list_del_init(&fl->fl_u.afs.link);
+}