sysfs: correctly handle read offset on PREALLOC attrs
authorKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Wed, 22 Jun 2016 18:42:16 +0000 (21:42 +0300)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Wed, 31 Aug 2016 13:14:44 +0000 (15:14 +0200)
commit17d0774f80681020eccc9638d925a23f1fc4f671
treefb44854ba2ae18413b567fc0fec3f612f43580e0
parent96b0af4b729cabd44e237c5a6b9bd4e0ea4ed457
sysfs: correctly handle read offset on PREALLOC attrs

Attributes declared with __ATTR_PREALLOC use sysfs_kf_read() which returns
zero bytes for non-zero offset. This breaks script checkarray in mdadm tool
in debian where /bin/sh is 'dash' because its builtin 'read' reads only one
byte at a time. Script gets 'i' instead of 'idle' when reads current action
from /sys/block/$dev/md/sync_action and as a result does nothing.

This patch adds trivial implementation of partial read: generate whole
string and move required part into buffer head.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Fixes: 4ef67a8c95f3 ("sysfs/kernfs: make read requests on pre-alloc files use the buffer.")
Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787950
Cc: Stable <stable@vger.kernel.org> # v3.19+
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
fs/sysfs/file.c