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 0000000..8f07f8d1
--- /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);
+}