On Mon, Nov 28, 2016 at 4:11 PM, Tomasz Majchrzak
<tomasz.majchr...@intel.com> wrote:
> If kernfs file is empty on a first read, successive read operations
> using the same file descriptor will return no data, even when data is
> available. Default kernfs 'seq_next' implementation advances iterator
> position even when next object is not there. Kernfs 'seq_start' for
> following requests will not return iterator as position is already on
> the second object.
>
> This defect doesn't allow to monitor badblocks sysfs files from MD raid.
> They are initially empty but if data appears at some stage, userspace is
> not able to read it.
>
> Signed-off-by: Tomasz Majchrzak <tomasz.majchr...@intel.com>
A comment above the check wouldn't hurt. Otherwise
Acked-by: Miklos Szeredi <mszer...@redhat.com>
> ---
> fs/seq_file.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/seq_file.c b/fs/seq_file.c
> index 368bfb9..ee21714 100644
> --- a/fs/seq_file.c
> +++ b/fs/seq_file.c
> @@ -190,6 +190,9 @@ ssize_t seq_read(struct file *file, char __user *buf,
> size_t size, loff_t *ppos)
> */
> m->version = file->f_version;
>
> + if (*ppos == 0)
> + m->index = 0;
> +
> /* Don't assume *ppos is where we left it */
> if (unlikely(*ppos != m->read_pos)) {
> while ((err = traverse(m, *ppos)) == -EAGAIN)
> --
> 1.8.3.1
>
