path: root/fs/sysfs
diff options
authorKonstantin Khlebnikov <>2016-06-22 21:42:16 +0300
committerGreg Kroah-Hartman <>2016-08-31 15:14:44 +0200
commit17d0774f80681020eccc9638d925a23f1fc4f671 (patch)
treefb44854ba2ae18413b567fc0fec3f612f43580e0 /fs/sysfs
parent96b0af4b729cabd44e237c5a6b9bd4e0ea4ed457 (diff)
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: Cc: Stable <> # v3.19+ Acked-by: Tejun Heo <> Signed-off-by: Greg Kroah-Hartman <>
Diffstat (limited to 'fs/sysfs')
1 files changed, 7 insertions, 1 deletions
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);