patch "sysfs: correctly handle read offset on PREALLOC attrs" added to driver-core-linus

This is a note to let you know that I've just added the patch titled

sysfs: correctly handle read offset on PREALLOC attrs

to my driver-core git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git
in the driver-core-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From: Konstantin Khlebnikov <[email protected]>
Date: Wed, 22 Jun 2016 21:42:16 +0300
Subject: 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.

---
 fs/sysfs/file.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

index f35523d4fa3a..b803213d1307 100644
@@ -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);
 }
 

2.9.3