[PATCH v2] loop: Disable fallocate() zero and discard if not supported

[PATCH v2] loop: Disable fallocate() zero and discard if not supported

[Cyril Hrubis]

If fallcate is implemented but zero and discard operations are not
supported by the filesystem the backing file is on we continue to fill
dmesg with errors from the blk_mq_end_request() since each time we call
fallocate() on the loop device the EOPNOTSUPP error from lo_fallocate()
ends up propagated into the block layer. In the end syscall succeeds
since the blkdev_issue_zeroout() falls back to writing zeroes which
makes the errors even more misleading and confusing.

How to reproduce:

1. make sure /tmp is mounted as tmpfs
2. dd if=/dev/zero of=/tmp/disk.img bs=1M count=100
3. losetup /dev/loop0 /tmp/disk.img
4. mkfs.ext2 /dev/loop0
5. dmesg |tail

[710690.898214] operation not supported error, dev loop0, sector 204672 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
[710690.898279] operation not supported error, dev loop0, sector 522 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
[710690.898603] operation not supported error, dev loop0, sector 16906 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
[710690.898917] operation not supported error, dev loop0, sector 32774 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
[710690.899218] operation not supported error, dev loop0, sector 49674 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
[710690.899484] operation not supported error, dev loop0, sector 65542 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
[710690.899743] operation not supported error, dev loop0, sector 82442 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
[710690.900015] operation not supported error, dev loop0, sector 98310 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
[710690.900276] operation not supported error, dev loop0, sector 115210 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
[710690.900546] operation not supported error, dev loop0, sector 131078 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0

This patch changes the lo_fallocate() to clear the flags for zero and
discard operations if we get EOPNOTSUPP from the backing file fallocate
callback, that way we at least stop spewing errors after the first
unsuccessful try.

CC: Jan Kara <jack@suse.cz>
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
---

v2:
   - move the code into a separate function
   - use unlikely() in the condigtion

 drivers/block/loop.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 93780f41646b..1153721bc7c2 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -302,6 +302,21 @@ static int lo_read_simple(struct loop_device *lo, struct request *rq,
 	return 0;
 }
 
+static void loop_clear_limits(struct loop_device *lo, int mode)
+{
+	struct queue_limits lim = queue_limits_start_update(lo->lo_queue);
+
+	if (mode & FALLOC_FL_ZERO_RANGE)
+		lim.max_write_zeroes_sectors = 0;
+
+	if (mode & FALLOC_FL_PUNCH_HOLE) {
+		lim.max_hw_discard_sectors = 0;
+		lim.discard_granularity = 0;
+	}
+
+	queue_limits_commit_update(lo->lo_queue, &lim);
+}
+
 static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
 			int mode)
 {
@@ -320,6 +335,14 @@ static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
 	ret = file->f_op->fallocate(file, mode, pos, blk_rq_bytes(rq));
 	if (unlikely(ret && ret != -EINVAL && ret != -EOPNOTSUPP))
 		return -EIO;
+
+	/*
+	 * We initially configure the limits in a hope that fallocate is
+	 * supported and clear them here if that turns out not to be true.
+	 */
+	if (unlikely(ret == -EOPNOTSUPP))
+		loop_clear_limits(lo, mode);
+
 	return ret;
 }
 
-- 
2.44.2

Re: [PATCH v2] loop: Disable fallocate() zero and discard if not supported

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v2] loop: Disable fallocate() zero and discard if not supported

[Jan Kara]

On Thu 13-06-24 18:38:17, Cyril Hrubis wrote:
> If fallcate is implemented but zero and discard operations are not
     ^^^ fallocate

> supported by the filesystem the backing file is on we continue to fill
> dmesg with errors from the blk_mq_end_request() since each time we call
> fallocate() on the loop device the EOPNOTSUPP error from lo_fallocate()
> ends up propagated into the block layer. In the end syscall succeeds
> since the blkdev_issue_zeroout() falls back to writing zeroes which
> makes the errors even more misleading and confusing.
> 
> How to reproduce:
> 
> 1. make sure /tmp is mounted as tmpfs
> 2. dd if=/dev/zero of=/tmp/disk.img bs=1M count=100
> 3. losetup /dev/loop0 /tmp/disk.img
> 4. mkfs.ext2 /dev/loop0
> 5. dmesg |tail
> 
> [710690.898214] operation not supported error, dev loop0, sector 204672 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
> [710690.898279] operation not supported error, dev loop0, sector 522 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
> [710690.898603] operation not supported error, dev loop0, sector 16906 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
> [710690.898917] operation not supported error, dev loop0, sector 32774 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
> [710690.899218] operation not supported error, dev loop0, sector 49674 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
> [710690.899484] operation not supported error, dev loop0, sector 65542 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
> [710690.899743] operation not supported error, dev loop0, sector 82442 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
> [710690.900015] operation not supported error, dev loop0, sector 98310 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
> [710690.900276] operation not supported error, dev loop0, sector 115210 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
> [710690.900546] operation not supported error, dev loop0, sector 131078 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
> 
> This patch changes the lo_fallocate() to clear the flags for zero and
> discard operations if we get EOPNOTSUPP from the backing file fallocate
> callback, that way we at least stop spewing errors after the first
> unsuccessful try.
> 
> CC: Jan Kara <jack@suse.cz>
> Signed-off-by: Cyril Hrubis <chrubis@suse.cz>

Thanks. Besides the spelling fix the patch looks good to me. Feel free to
add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

>  drivers/block/loop.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 93780f41646b..1153721bc7c2 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -302,6 +302,21 @@ static int lo_read_simple(struct loop_device *lo, struct request *rq,
>  	return 0;
>  }
>  
> +static void loop_clear_limits(struct loop_device *lo, int mode)
> +{
> +	struct queue_limits lim = queue_limits_start_update(lo->lo_queue);
> +
> +	if (mode & FALLOC_FL_ZERO_RANGE)
> +		lim.max_write_zeroes_sectors = 0;
> +
> +	if (mode & FALLOC_FL_PUNCH_HOLE) {
> +		lim.max_hw_discard_sectors = 0;
> +		lim.discard_granularity = 0;
> +	}
> +
> +	queue_limits_commit_update(lo->lo_queue, &lim);
> +}
> +
>  static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
>  			int mode)
>  {
> @@ -320,6 +335,14 @@ static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
>  	ret = file->f_op->fallocate(file, mode, pos, blk_rq_bytes(rq));
>  	if (unlikely(ret && ret != -EINVAL && ret != -EOPNOTSUPP))
>  		return -EIO;
> +
> +	/*
> +	 * We initially configure the limits in a hope that fallocate is
> +	 * supported and clear them here if that turns out not to be true.
> +	 */
> +	if (unlikely(ret == -EOPNOTSUPP))
> +		loop_clear_limits(lo, mode);
> +
>  	return ret;
>  }
>  
> -- 
> 2.44.2
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH v2] loop: Disable fallocate() zero and discard if not supported

[Jens Axboe]

On Thu, 13 Jun 2024 18:38:17 +0200, Cyril Hrubis wrote:
> If fallcate is implemented but zero and discard operations are not
> supported by the filesystem the backing file is on we continue to fill
> dmesg with errors from the blk_mq_end_request() since each time we call
> fallocate() on the loop device the EOPNOTSUPP error from lo_fallocate()
> ends up propagated into the block layer. In the end syscall succeeds
> since the blkdev_issue_zeroout() falls back to writing zeroes which
> makes the errors even more misleading and confusing.
> 
> [...]

Applied, thanks!

[1/1] loop: Disable fallocate() zero and discard if not supported
      commit: 5f75e081ab5cbfbe7aca2112a802e69576ee9778

Best regards,
-- 
Jens Axboe