[PATCH] kernfs: handle poll correctly on 'direct_read' files.

[PATCH] kernfs: handle poll correctly on 'direct_read' files.

[NeilBrown]

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Kernfs supports two styles of read: direct_read and seqfile_read.

The latter supports 'poll' correctly thanks to the update of
'->event' in kernfs_seq_show.
The former does not as '->event' is never updated on a read.

So add an appropriate update in kernfs_file_direct_read().

This was noticed because some 'md' sysfs attributes were
recently changed to use direct reads.

Reported-by: Prakash Punnoor <prakash@punnoor.de>
Reported-by: Torsten Kaiser <just.for.lkml@googlemail.com>
Fixes: 750f199ee8b578062341e6ddfe36c59ac8ff2dcb
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index b684e8a132e6..2bacb9988566 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -207,6 +207,7 @@ static ssize_t kernfs_file_direct_read(struct kernfs_open_file *of,
 		goto out_free;
 	}
 
+	of->event = atomic_read(&of->kn->attr.open->event);
 	ops = kernfs_ops(of->kn);
 	if (ops->read)
 		len = ops->read(of, buf, len, *ppos);

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Re: [PATCH] kernfs: handle poll correctly on 'direct_read' files.

[Tejun Heo]

On Mon, Mar 16, 2015 at 10:44:52AM +1100, NeilBrown wrote:
> 
> 
> Kernfs supports two styles of read: direct_read and seqfile_read.
> 
> The latter supports 'poll' correctly thanks to the update of
> '->event' in kernfs_seq_show.
> The former does not as '->event' is never updated on a read.
> 
> So add an appropriate update in kernfs_file_direct_read().
> 
> This was noticed because some 'md' sysfs attributes were
> recently changed to use direct reads.
> 
> Reported-by: Prakash Punnoor <prakash@punnoor.de>
> Reported-by: Torsten Kaiser <just.for.lkml@googlemail.com>
> Fixes: 750f199ee8b578062341e6ddfe36c59ac8ff2dcb

This fixes tag is kinda weird without further explanation.

> Signed-off-by: NeilBrown <neilb@suse.de>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun