Commit e522751d authored by Tomasz Majchrzak's avatar Tomasz Majchrzak Committed by Al Viro

seq_file: reset iterator to first record for zero offset

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: default avatarTomasz Majchrzak <tomasz.majchrzak@intel.com>
Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 22725ce4
...@@ -190,6 +190,13 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos) ...@@ -190,6 +190,13 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
*/ */
m->version = file->f_version; m->version = file->f_version;
/*
* if request is to read from zero offset, reset iterator to first
* record as it might have been already advanced by previous requests
*/
if (*ppos == 0)
m->index = 0;
/* Don't assume *ppos is where we left it */ /* Don't assume *ppos is where we left it */
if (unlikely(*ppos != m->read_pos)) { if (unlikely(*ppos != m->read_pos)) {
while ((err = traverse(m, *ppos)) == -EAGAIN) while ((err = traverse(m, *ppos)) == -EAGAIN)
......
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