On Mon, 18 Aug 2008 21:28:56 +0900
Takashi Sato <t-sato@xxxxxxxxxxxxx> wrote:
The timeout feature is added to freeze ioctl. And new ioctl
to reset the timeout period is added.
o Freeze the filesystem
int ioctl(int fd, int FIFREEZE, long *timeout_sec)
fd: The file descriptor of the mountpoint
FIFREEZE: request code for the freeze
timeout_sec: the timeout period in seconds
If it's 0 or 1, the timeout isn't set.
This special case of "1" is implemented to keep
the compatibility with XFS applications.
Return value: 0 if the operation succeeds. Otherwise, -1
o Reset the timeout period
int ioctl(int fd, int FIFREEZE_RESET_TIMEOUT, long *timeout_sec)
fd:file descriptor of mountpoint
FIFREEZE_RESET_TIMEOUT: request code for reset of timeout period
timeout_sec: new timeout period in seconds
Return value: 0 if the operation succeeds. Otherwise, -1
Error number: If the filesystem has already been unfrozen,
errno is set to EINVAL.
I don't think the changelogs actually explained why this feature is
being added?
Which userspace tools are expected to send these ioctls? Something in
util-linux? dm-utils? Are patches to those packages planned?
...
/*
+ * ioctl_freeze_reset_timeout - Reset timeout for freeze.
+ *
+ * @filp: target file
+ * @argp: timeout value(sec)
+ *
+ * Reset timeout for freeze.
+ */
+static int
+ioctl_freeze_reset_timeout(struct file *filp, int __user *argp)
+{
+ int timeout_sec;
+ unsigned int timeout_msec;
+ struct super_block *sb = filp->f_path.dentry->d_inode->i_sb;
+ struct block_device *bdev = sb->s_bdev;
+ int error;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ /* If a regular file or a directory isn't specified, return EINVAL. */
+ if (bdev == NULL)
+ return -EINVAL;
+
+ /* arg(sec) to tick value */
+ error = get_user(timeout_sec, argp);
+ if (error)
+ return error;
+
+ if (timeout_sec <= 0 || timeout_sec > UINT_MAX/1000)
+ return -EINVAL;
+
+ timeout_msec = timeout_sec * 1000;
+
+ down(&bdev->bd_freeze_sem);
+ if (!bdev->bd_freeze_count) {
+ up(&bdev->bd_freeze_sem);
+ return -EINVAL;
+ }
+ /* setup unfreeze timer */
+ add_freeze_timeout(bdev, timeout_msec);
+ up(&bdev->bd_freeze_sem);
+
+ return 0;
+}
This duplicates quite a bit of code from ioctl_freeze(). Can this be
cleaned up?
+/*
* When you add any new common ioctls to the switches above and below
* please update compat_sys_ioctl() too.
*
@@ -235,13 +302,17 @@ int do_vfs_ioctl(struct file *filp, unsi
break;
case FIFREEZE:
- error = ioctl_freeze(filp);
+ error = ioctl_freeze(filp, argp);
break;
case FITHAW:
error = ioctl_thaw(filp);
break;
+ case FIFREEZE_RESET_TIMEOUT:
+ error = ioctl_freeze_reset_timeout(filp, argp);
+ break;
+
default:
if (S_ISREG(filp->f_path.dentry->d_inode->i_mode))
error = file_ioctl(filp, cmd, arg);
...
EXPORT_SYMBOL_GPL(kern_mount_data);
+
+/*
+ * freeze_timeout - Thaw the filesystem.
+ *
+ * @work: work queue (delayed_work.work)
+ *
+ * Called by the delayed work when elapsing the timeout period.
+ * Thaw the filesystem.
+ */
+void freeze_timeout(struct work_struct *work)
+{
+ struct block_device *bd = container_of(work,
+ struct block_device, bd_freeze_timeout.work);
+ struct super_block *sb = get_super(bd);
+
+ thaw_bdev(bd, sb);
+
+ if (sb)
+ drop_super(sb);
+}
+EXPORT_SYMBOL_GPL(freeze_timeout);
I can't see why this was exported.
+/*
+ * add_freeze_timeout - Add timeout for freeze.
+ *
+ * @bdev: block device struct
+ * @timeout_msec: timeout period
+ *
+ * Add the delayed work for freeze timeout to the delayed work queue.
+ */
+void add_freeze_timeout(struct block_device *bdev, unsigned int timeout_msec)
+{
+ s64 timeout_jiffies = msecs_to_jiffies(timeout_msec);
+
+ /* Set delayed work queue */
+ cancel_delayed_work_sync(&bdev->bd_freeze_timeout);
+ schedule_delayed_work(&bdev->bd_freeze_timeout, timeout_jiffies);
+}
I don't particularly like the names of these new global symbols. The
kernel already has a "freezer" thing, part of power-management. Introducing another one is a bit confusing.
otoh, freezer seems to have consistently used "freezer", so the 'r'
arguable saves us.
Still, I'd have thought that "fsfreeze" would have been a clearer, more
specific identifier for the whole project.
+/*
+ * del_freeze_timeout - Delete timeout for freeze.
+ *
+ * @bdev: block device struct
+ *
+ * Delete the delayed work for freeze timeout from the delayed work queue.
+ */
+void del_freeze_timeout(struct block_device *bdev)
+{
+ /*
+ * It's possible that the delayed work task (freeze_timeout()) calls
+ * del_freeze_timeout(). If the delayed work task calls
+ * cancel_delayed_work_sync((), the deadlock will occur.
+ * So we need this check (delayed_work_pending()).
+ */
+ if (delayed_work_pending(&bdev->bd_freeze_timeout))
+ cancel_delayed_work_sync(&bdev->bd_freeze_timeout);
+}
So if the calling task is keventd via run_workqueue() then
delayed_work_pending() should return false due to run_workqueue()
ordering, so we avoid the deadlock.
Seems a bit racy if some other process starts the delayed-work while
this function is running but I guess the new semaphore prevents that.
Perhaps cancel_delayed_work_sync() shouldn't hang up if called from the
work handler?