[ adding Al ] On Tue, Aug 23, 2016 at 2:19 AM, Tomasz Majchrzak <[email protected]> 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. > > Don't set read position if valid iterator has not been returned.
Can you say a bit about how you found this? So we have an idea about userspace tooling is broken by this bug. > > Signed-off-by: Tomasz Majchrzak <[email protected]> I would add "Cc: <[email protected]>" to the next version of this patch. > fs/seq_file.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/seq_file.c b/fs/seq_file.c > index 19f532e..893db43 100644 > --- a/fs/seq_file.c > +++ b/fs/seq_file.c > @@ -242,7 +242,8 @@ ssize_t seq_read(struct file *file, char __user *buf, > size_t size, loff_t *ppos) > m->count = 0; > if (unlikely(!m->count)) { > p = m->op->next(m, p, &pos); > - m->index = pos; > + if (p && !IS_ERR(p)) Lets change this to use the IS_ERR_OR_NULL() helper, and do the same with the earlier if (!p || IS_ERR()) a few lines up in the loop. Other than that, this looks good to me. Reviewed-by: Dan Williams <[email protected]>
