[PATCH] md: Fix missing unused status line of /proc/mdstat

[PATCH] md: Fix missing unused status line of /proc/mdstat

[Jan Glauber]

Reading /proc/mdstat with a read buffer size that would not
fit the unused status line in the first read will skip this
line from the output.

So 'dd if=/proc/mdstat bs=64 2>/dev/null' will not print something
like: unused devices: <none>

Don't return NULL immediately in start() for v=2 but call
show() once to print the status line also for multiple reads.

Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface")
Signed-off-by: Jan Glauber <jglauber@digitalocean.com>
---
 drivers/md/md.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 21da0c48f6c2..cb19d50fa672 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8153,7 +8153,11 @@ static void *md_seq_start(struct seq_file *seq, loff_t *pos)
 	loff_t l = *pos;
 	struct mddev *mddev;
 
-	if (l >= 0x10000)
+	if (l == 0x10000) {
+		++*pos;
+		return (void *)2;
+	}
+	if (l > 0x10000)
 		return NULL;
 	if (!l--)
 		/* header */
-- 
2.17.1

Re: [PATCH] md: Fix missing unused status line of /proc/mdstat

[Song Liu]

On Wed, Mar 17, 2021 at 7:05 AM Jan Glauber <jglauber@digitalocean.com> wrote:
>
> Reading /proc/mdstat with a read buffer size that would not
> fit the unused status line in the first read will skip this
> line from the output.
>
> So 'dd if=/proc/mdstat bs=64 2>/dev/null' will not print something
> like: unused devices: <none>
>
> Don't return NULL immediately in start() for v=2 but call
> show() once to print the status line also for multiple reads.
>
> Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface")
> Signed-off-by: Jan Glauber <jglauber@digitalocean.com>

Applied to md-next. Thanks!
Song