[PATCH driver-core] kernfs: fix regression in kernfs_fop_write caused by wrong type

[Ivan Vecera <ivecera@redhat.com>]

Commit b7ce40cff0b9 ("kernfs: cache atomic_write_len in
kernfs_open_file") changes type of local variable 'len' from ssize_t
to size_t. This change caused that the *ppos value is updated also
when the previous write callback failed.

Mentioned snippet:
...
len = ops->write(...); <- return value can be negative
...
if (len > 0)           <- true here in this case
        *ppos += len;
...

Fixes: b7ce40cff0b9 ("kernfs: cache atomic_write_len in kernfs_open_file")
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
---
 fs/kernfs/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 9698e51656b1..d8f49c412f50 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -275,7 +275,7 @@ static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,
 {
 	struct kernfs_open_file *of = kernfs_of(file);
 	const struct kernfs_ops *ops;
-	size_t len;
+	ssize_t len;
 	char *buf;
 
 	if (of->atomic_write_len) {
-- 
2.13.6