vhost-user: Drop misleading EAGAIN checks in slave_read()

slave_read() checks EAGAIN when reading or writing to the socket
fails. This gives the impression that the slave channel is in
non-blocking mode, which is certainly not the case with the current
code base. And the rest of the code isn't actually ready to cope
with non-blocking I/O.

Just drop the checks everywhere in this function for the sake of
clarity.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <20210312092212.782255-2-groug@kaod.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

hw/virtio/vhost-user.c

@@ -1420,7 +1420,7 @@ static void slave_read(void *opaque)
 
     do {
         size = recvmsg(u->slave_fd, &msgh, 0);
-    } while (size < 0 && (errno == EINTR || errno == EAGAIN));
+    } while (size < 0 && errno == EINTR);
 
     if (size != VHOST_USER_HDR_SIZE) {
         error_report("Failed to read from slave.");
@@ -1452,7 +1452,7 @@ static void slave_read(void *opaque)
     /* Read payload */
     do {
         size = read(u->slave_fd, &payload, hdr.size);
-    } while (size < 0 && (errno == EINTR || errno == EAGAIN));
+    } while (size < 0 && errno == EINTR);
 
     if (size != hdr.size) {
         error_report("Failed to read payload from slave.");
@@ -1503,7 +1503,7 @@ static void slave_read(void *opaque)
 
         do {
             size = writev(u->slave_fd, iovec, ARRAY_SIZE(iovec));
-        } while (size < 0 && (errno == EINTR || errno == EAGAIN));
+        } while (size < 0 && errno == EINTR);
 
         if (size != VHOST_USER_HDR_SIZE + hdr.size) {
             error_report("Failed to send msg reply to slave.");