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| author | Konstantin Khlebnikov <khlebnikov@yandex-team.ru> | 2016-06-22 21:42:16 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-09-07 08:34:56 +0200 |
| commit | 95f837790b66c770d94625206e0cc178df984635 (patch) | |
| tree | c66367b439b541f00ae7bb05f662e7ce65f6076e | |
| parent | 34242c449ae7753772b68436efef5679a0726cf4 (diff) | |
| download | lwn-95f837790b66c770d94625206e0cc178df984635.tar.gz lwn-95f837790b66c770d94625206e0cc178df984635.zip | |
sysfs: correctly handle read offset on PREALLOC attrs
commit 17d0774f80681020eccc9638d925a23f1fc4f671 upstream.
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
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | fs/sysfs/file.c | 8 |
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); } |