xenfs/xenbus: report partial reads/writes correctly

copy_(to|from)_user return the number of uncopied bytes, so a successful
return is 0, and any non-zero result indicates some degree of failure.

Reported-by: "Jun Zhu (Intern)" <Jun.Zhu@citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/xen/xenfs/xenbus.c b/drivers/xen/xenfs/xenbus.c
index 9d5b519d2e4..d2a90582680 100644
--- a/drivers/xen/xenfs/xenbus.c
+++ b/drivers/xen/xenfs/xenbus.c
@@ -142,7 +142,7 @@ static ssize_t xenbus_file_read(struct file *filp,
                 i += sz - ret;
                 rb->cons += sz - ret;
 
-                if (ret != sz) {
+                if (ret != 0) {
                         if (i == 0)
                                 i = -EFAULT;
                         goto out;
@@ -453,7 +453,7 @@ static ssize_t xenbus_file_write(struct file *filp,
 
         ret = copy_from_user(u->u.buffer + u->len, ubuf, len);
 
-        if (ret == len) {
+        if (ret != 0) {
                 rc = -EFAULT;
                 goto out;
         }