From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org
Cc: NeilBrown <neilb@suse.de>, Tejun Heo <tj@kernel.org>,
stable@vger.kernel.org
Subject: [PATCH] sysfs: correctly handle read offset on PREALLOC attrs
Date: Wed, 22 Jun 2016 21:42:16 +0300 [thread overview]
Message-ID: <146662093622.3726.10220135910756738018.stgit@buzz> (raw)
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+
---
fs/sysfs/file.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index f35523d4fa3a..b803213d1307 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -114,9 +114,15 @@ static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
* If buf != of->prealloc_buf, we don't know how
* large it is, so cannot safely pass it to ->show
*/
- if (pos || WARN_ON_ONCE(buf != of->prealloc_buf))
+ if (WARN_ON_ONCE(buf != of->prealloc_buf))
return 0;
len = ops->show(kobj, of->kn->priv, buf);
+ if (pos) {
+ if (len <= pos)
+ return 0;
+ len -= pos;
+ memmove(buf, buf + pos, len);
+ }
return min(count, len);
}
next reply other threads:[~2016-06-22 18:42 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-22 18:42 Konstantin Khlebnikov [this message]
2016-06-23 21:18 ` [PATCH] sysfs: correctly handle read offset on PREALLOC attrs Tejun Heo
2016-09-05 13:25 ` Konstantin Khlebnikov
2016-09-05 13:46 ` Greg Kroah-Hartman
2016-09-05 14:02 ` Konstantin Khlebnikov
2016-09-05 14:15 ` Greg Kroah-Hartman
2016-09-05 14:13 ` Greg Kroah-Hartman
2016-09-05 14:17 ` Konstantin Khlebnikov
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