From 17d0774f80681020eccc9638d925a23f1fc4f671 Mon Sep 17 00:00:00 2001 From: Konstantin Khlebnikov Date: Wed, 22 Jun 2016 21:42:16 +0300 Subject: [PATCH] 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 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 # v3.19+ Acked-by: Tejun Heo Signed-off-by: Greg Kroah-Hartman --- 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); }