um: virtio: fix handling of messages without payload

If we have a message without payload, we call full_read() with
len set to 0, which causes it to return -ECONNRESET. Catch this
case and explicitly return 0 for it so we can actually use the
zero-size config-changed message.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

diff --git a/arch/um/drivers/virtio_uml.c b/arch/um/drivers/virtio_uml.c
index 515d648..ef620ca 100644 (file)
--- a/arch/um/drivers/virtio_uml.c
+++ b/arch/um/drivers/virtio_uml.c
@@ -97,6 +97,9 @@ static int full_read(int fd, void *buf, int len, bool abortable)
 {
        int rc;
 
+       if (!len)
+               return 0;
+
        do {
                rc = os_read_file(fd, buf, len);
                if (rc > 0) {