Btrfs: wait for quota rescan to complete

Btrfs: wait for quota rescan to complete

[Jan Schmidt]

Two small patches, one for the kernel and one for the user mode. Both
required to support waiting for quota rescan to complete.

Jan Schmidt (1):
  Btrfs: add ioctl to wait for qgroup rescan completion

 fs/btrfs/ctree.h           |    2 ++
 fs/btrfs/ioctl.c           |   12 ++++++++++++
 fs/btrfs/qgroup.c          |   21 +++++++++++++++++++++
 include/uapi/linux/btrfs.h |    1 +
 4 files changed, 36 insertions(+), 0 deletions(-)


Jan Schmidt (2):
  Btrfs-progs: fixup: add flags to struct btrfs_ioctl_quota_rescan_args
  Btrfs-progs: added "btrfs quota rescan" -w switch (wait)

 cmds-quota.c |   19 +++++++++++++++++--
 ioctl.h      |    2 ++
 2 files changed, 19 insertions(+), 2 deletions(-)

[PATCH] Btrfs: add ioctl to wait for qgroup rescan completion

[Jan Schmidt]

btrfs_qgroup_wait_for_completion waits until the currently running qgroup
operation completes. It returns immediately when no rescan process is in
progress. This is useful to automate things around the rescan process (e.g.
testing).

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
---
 fs/btrfs/ctree.h           |    2 ++
 fs/btrfs/ioctl.c           |   12 ++++++++++++
 fs/btrfs/qgroup.c          |   21 +++++++++++++++++++++
 include/uapi/linux/btrfs.h |    1 +
 4 files changed, 36 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 8624f49..39ca0d9 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1607,6 +1607,7 @@ struct btrfs_fs_info {
 	struct mutex qgroup_rescan_lock; /* protects the progress item */
 	struct btrfs_key qgroup_rescan_progress;
 	struct btrfs_workers qgroup_rescan_workers;
+	struct completion qgroup_rescan_completion;
 
 	/* filesystem state */
 	unsigned long fs_state;
@@ -3836,6 +3837,7 @@ int btrfs_quota_enable(struct btrfs_trans_handle *trans,
 int btrfs_quota_disable(struct btrfs_trans_handle *trans,
 			struct btrfs_fs_info *fs_info);
 int btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info);
+int btrfs_qgroup_wait_for_completion(struct btrfs_fs_info *fs_info);
 int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans,
 			      struct btrfs_fs_info *fs_info, u64 src, u64 dst);
 int btrfs_del_qgroup_relation(struct btrfs_trans_handle *trans,
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 5e93bb8..9161660 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3937,6 +3937,16 @@ static long btrfs_ioctl_quota_rescan_status(struct file *file, void __user *arg)
 	return ret;
 }
 
+static long btrfs_ioctl_quota_rescan_wait(struct file *file, void __user *arg)
+{
+	struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	return btrfs_qgroup_wait_for_completion(root->fs_info);
+}
+
 static long btrfs_ioctl_set_received_subvol(struct file *file,
 					    void __user *arg)
 {
@@ -4179,6 +4189,8 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_quota_rescan(file, argp);
 	case BTRFS_IOC_QUOTA_RESCAN_STATUS:
 		return btrfs_ioctl_quota_rescan_status(file, argp);
+	case BTRFS_IOC_QUOTA_RESCAN_WAIT:
+		return btrfs_ioctl_quota_rescan_wait(file, argp);
 	case BTRFS_IOC_DEV_REPLACE:
 		return btrfs_ioctl_dev_replace(root, argp);
 	case BTRFS_IOC_GET_FSLABEL:
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 9d49c58..ebca17a 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -2068,6 +2068,8 @@ out:
 	} else {
 		pr_err("btrfs: qgroup scan failed with %d\n", err);
 	}
+
+	complete_all(&fs_info->qgroup_rescan_completion);
 }
 
 static void
@@ -2108,6 +2110,7 @@ btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info)
 	fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_RESCAN;
 	memset(&fs_info->qgroup_rescan_progress, 0,
 		sizeof(fs_info->qgroup_rescan_progress));
+	init_completion(&fs_info->qgroup_rescan_completion);
 
 	/* clear all current qgroup tracking information */
 	for (n = rb_first(&fs_info->qgroup_tree); n; n = rb_next(n)) {
@@ -2124,3 +2127,21 @@ btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info)
 
 	return 0;
 }
+
+int btrfs_qgroup_wait_for_completion(struct btrfs_fs_info *fs_info)
+{
+	int running;
+	int ret = 0;
+
+	mutex_lock(&fs_info->qgroup_rescan_lock);
+	spin_lock(&fs_info->qgroup_lock);
+	running = fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN;
+	spin_unlock(&fs_info->qgroup_lock);
+	mutex_unlock(&fs_info->qgroup_rescan_lock);
+
+	if (running)
+		ret = wait_for_completion_interruptible(
+					&fs_info->qgroup_rescan_completion);
+
+	return ret;
+}
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 5ef0df5..5b683b5 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -530,6 +530,7 @@ struct btrfs_ioctl_send_args {
 			       struct btrfs_ioctl_quota_rescan_args)
 #define BTRFS_IOC_QUOTA_RESCAN_STATUS _IOR(BTRFS_IOCTL_MAGIC, 45, \
 			       struct btrfs_ioctl_quota_rescan_args)
+#define BTRFS_IOC_QUOTA_RESCAN_WAIT _IO(BTRFS_IOCTL_MAGIC, 46)
 #define BTRFS_IOC_GET_FSLABEL _IOR(BTRFS_IOCTL_MAGIC, 49, \
 				   char[BTRFS_LABEL_SIZE])
 #define BTRFS_IOC_SET_FSLABEL _IOW(BTRFS_IOCTL_MAGIC, 50, \
-- 
1.7.1

Re: [PATCH] Btrfs: add ioctl to wait for qgroup rescan completion

[David Sterba]

On Mon, May 06, 2013 at 09:14:17PM +0200, Jan Schmidt wrote:
> --- a/include/uapi/linux/btrfs.h
> +++ b/include/uapi/linux/btrfs.h
> @@ -530,6 +530,7 @@ struct btrfs_ioctl_send_args {
>  			       struct btrfs_ioctl_quota_rescan_args)
>  #define BTRFS_IOC_QUOTA_RESCAN_STATUS _IOR(BTRFS_IOCTL_MAGIC, 45, \
>  			       struct btrfs_ioctl_quota_rescan_args)
> +#define BTRFS_IOC_QUOTA_RESCAN_WAIT _IO(BTRFS_IOCTL_MAGIC, 46)

Why do you need an ioctl when the same can be achieved by polling the
RESCAN_STATUS value ? The code does not anything special that has to be
done within kernel.

david

Re: [PATCH] Btrfs: add ioctl to wait for qgroup rescan completion

[Jan Schmidt]

On Mon, May 06, 2013 at 23:20 (+0200), David Sterba wrote:
> On Mon, May 06, 2013 at 09:14:17PM +0200, Jan Schmidt wrote:
>> --- a/include/uapi/linux/btrfs.h
>> +++ b/include/uapi/linux/btrfs.h
>> @@ -530,6 +530,7 @@ struct btrfs_ioctl_send_args {
>>  			       struct btrfs_ioctl_quota_rescan_args)
>>  #define BTRFS_IOC_QUOTA_RESCAN_STATUS _IOR(BTRFS_IOCTL_MAGIC, 45, \
>>  			       struct btrfs_ioctl_quota_rescan_args)
>> +#define BTRFS_IOC_QUOTA_RESCAN_WAIT _IO(BTRFS_IOCTL_MAGIC, 46)
> 
> Why do you need an ioctl when the same can be achieved by polling the
> RESCAN_STATUS value ? The code does not anything special that has to be
> done within kernel.

It's because I don't like polling :-) A rescan can take hours to complete, and
you wouldn't like to see one ioctl per second for such a period either, I guess.
(Plus: Everybody would lose like .9 seconds for each run of the xfstest I'm
writing - accumulates to ages at least!)

If you're worried about ioctl numbers, we could turn it into flags for
BTRFS_IOC_QUOTA_RESCAN, but I don't see we're short on ioctl numbers yet. The
reason why I chose a separate ioctl is that it is more like an attach operation
to support both, specifying it when starting a fresh scan and waiting for a scan
that's already running. I find it more intuitive to have it separate.

-Jan

Re: [PATCH] Btrfs: add ioctl to wait for qgroup rescan completion

[David Sterba]

On Tue, May 07, 2013 at 08:17:12AM +0200, Jan Schmidt wrote:
> On Mon, May 06, 2013 at 23:20 (+0200), David Sterba wrote:
> > On Mon, May 06, 2013 at 09:14:17PM +0200, Jan Schmidt wrote:
> >> --- a/include/uapi/linux/btrfs.h
> >> +++ b/include/uapi/linux/btrfs.h
> >> @@ -530,6 +530,7 @@ struct btrfs_ioctl_send_args {
> >>  			       struct btrfs_ioctl_quota_rescan_args)
> >>  #define BTRFS_IOC_QUOTA_RESCAN_STATUS _IOR(BTRFS_IOCTL_MAGIC, 45, \
> >>  			       struct btrfs_ioctl_quota_rescan_args)
> >> +#define BTRFS_IOC_QUOTA_RESCAN_WAIT _IO(BTRFS_IOCTL_MAGIC, 46)
> > 
> > Why do you need an ioctl when the same can be achieved by polling the
> > RESCAN_STATUS value ? The code does not anything special that has to be
> > done within kernel.
> 
> It's because I don't like polling :-) A rescan can take hours to complete, and
> you wouldn't like to see one ioctl per second for such a period either, I guess.
> (Plus: Everybody would lose like .9 seconds for each run of the xfstest I'm
> writing - accumulates to ages at least!)

> If you're worried about ioctl numbers, we could turn it into flags for
> BTRFS_IOC_QUOTA_RESCAN, but I don't see we're short on ioctl numbers yet.

Nah, not yet :)

A long operation? Then you can poll it every minute, with a configurable
polling interval of course. I don't see what's wrong with polling here,
the key information is provided and accessible.

Also, I don't like to see adding extra 32 bytes (struct completion) to
btrfs_fs_info when the rescan operation is going to be used very rarely.
(The long-term plan is to reduce size of this oversized structure.)

> The reason why I chose a separate ioctl is that it is more like an
> attach operation to support both, specifying it when starting a fresh
> scan and waiting for a scan that's already running. I find it more
> intuitive to have it separate.

I agree it's separate, from the user's side. But not necessarily from
the implementation side.

david

[PATCH 1/2] Btrfs-progs: fixup: add flags to struct btrfs_ioctl_quota_rescan_args

[Jan Schmidt]

The patch set previously sent was sent together with the kernel part, but
was not updated as I added some reserved bytes to the ioctl struct for
future compatibility. This fixes struct btrfs_ioctl_quota_rescan_args.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
---
 ioctl.h |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/ioctl.h b/ioctl.h
index 1ee631a..abe6dd4 100644
--- a/ioctl.h
+++ b/ioctl.h
@@ -429,6 +429,7 @@ struct btrfs_ioctl_quota_ctl_args {
 struct btrfs_ioctl_quota_rescan_args {
 	__u64	flags;
 	__u64   progress;
+	__u64   reserved[6];
 };
 
 struct btrfs_ioctl_qgroup_assign_args {
-- 
1.7.1

[PATCH 2/2] Btrfs-progs: added "btrfs quota rescan" -w switch (wait)

[Jan Schmidt]

With -w one can wait for a rescan operation to finish. It can be used when
starting a rescan operation or later to wait for the currently running
rescan operation to finish. Waiting is interruptible.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
---
 cmds-quota.c |   19 +++++++++++++++++--
 ioctl.h      |    1 +
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/cmds-quota.c b/cmds-quota.c
index 1169772..6557e83 100644
--- a/cmds-quota.c
+++ b/cmds-quota.c
@@ -90,10 +90,11 @@ static int cmd_quota_disable(int argc, char **argv)
 }
 
 static const char * const cmd_quota_rescan_usage[] = {
-	"btrfs quota rescan [-s] <path>",
+	"btrfs quota rescan [-sw] <path>",
 	"Trash all qgroup numbers and scan the metadata again with the current config.",
 	"",
 	"-s   show status of a running rescan operation",
+	"-w   wait for rescan operation to finish (can be already in progress)",
 	NULL
 };
 
@@ -105,21 +106,30 @@ static int cmd_quota_rescan(int argc, char **argv)
 	char *path = NULL;
 	struct btrfs_ioctl_quota_rescan_args args;
 	int ioctlnum = BTRFS_IOC_QUOTA_RESCAN;
+	int wait_for_completion = 0;
 
 	optind = 1;
 	while (1) {
-		int c = getopt(argc, argv, "s");
+		int c = getopt(argc, argv, "sw");
 		if (c < 0)
 			break;
 		switch (c) {
 		case 's':
 			ioctlnum = BTRFS_IOC_QUOTA_RESCAN_STATUS;
 			break;
+		case 'w':
+			wait_for_completion = 1;
+			break;
 		default:
 			usage(cmd_quota_rescan_usage);
 		}
 	}
 
+	if (ioctlnum != BTRFS_IOC_QUOTA_RESCAN && wait_for_completion) {
+		fprintf(stderr, "ERROR: -w cannot be used with -s\n");
+		return 12;
+	}
+
 	if (check_argc_exact(argc - optind, 1))
 		usage(cmd_quota_rescan_usage);
 
@@ -134,6 +144,11 @@ static int cmd_quota_rescan(int argc, char **argv)
 
 	ret = ioctl(fd, ioctlnum, &args);
 	e = errno;
+
+	if (wait_for_completion && (ret == 0 || e == EINPROGRESS)) {
+		ret = ioctl(fd, BTRFS_IOC_QUOTA_RESCAN_WAIT, &args);
+		e = errno;
+	}
 	close(fd);
 
 	if (ioctlnum == BTRFS_IOC_QUOTA_RESCAN) {
diff --git a/ioctl.h b/ioctl.h
index abe6dd4..c260bbf 100644
--- a/ioctl.h
+++ b/ioctl.h
@@ -529,6 +529,7 @@ struct btrfs_ioctl_clone_range_args {
 			       struct btrfs_ioctl_quota_rescan_args)
 #define BTRFS_IOC_QUOTA_RESCAN_STATUS _IOR(BTRFS_IOCTL_MAGIC, 45, \
 			       struct btrfs_ioctl_quota_rescan_args)
+#define BTRFS_IOC_QUOTA_RESCAN_WAIT _IO(BTRFS_IOCTL_MAGIC, 46)
 #define BTRFS_IOC_GET_FSLABEL _IOR(BTRFS_IOCTL_MAGIC, 49, \
 				   char[BTRFS_LABEL_SIZE])
 #define BTRFS_IOC_SET_FSLABEL _IOW(BTRFS_IOCTL_MAGIC, 50, \
-- 
1.7.1