[v6,04/12] vhost-user-server: do not set memory fd non-blocking

Commit Message

Stefano Garzarella May 28, 2024, 10:35 a.m. UTC

In vhost-user-server we set all fd received from the other peer
in non-blocking mode. For some of them (e.g. memfd, shm_open, etc.)
it's not really needed, because we don't use these fd with blocking
operations, but only to map memory.

In addition, in some systems this operation can fail (e.g. in macOS
setting an fd returned by shm_open() non-blocking fails with errno
= ENOTTY).

So, let's avoid setting fd non-blocking for those messages that we
know carry memory fd (e.g. VHOST_USER_ADD_MEM_REG,
VHOST_USER_SET_MEM_TABLE).

Reviewed-by: Daniel P. Berrangé <[e-mail]>
Acked-by: Stefan Hajnoczi <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Signed-off-by: Stefano Garzarella <[e-mail]>
---
v3:
- avoiding setting fd non-blocking for messages where we have memory fd
  (Eric)
---
 util/vhost-user-server.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

Patch

diff --git a/util/vhost-user-server.c b/util/vhost-user-server.c
index 3bfb1ad3ec..b19229074a 100644
--- a/util/vhost-user-server.c
+++ b/util/vhost-user-server.c
@@ -65,6 +65,18 @@  static void vmsg_close_fds(VhostUserMsg *vmsg)
 static void vmsg_unblock_fds(VhostUserMsg *vmsg)
 {
     int i;
+
+    /*
+     * These messages carry fd used to map memory, not to send/receive messages,
+     * so this operation is useless. In addition, in some systems this
+     * operation can fail (e.g. in macOS setting an fd returned by shm_open()
+     * non-blocking fails with errno = ENOTTY)
+     */
+    if (vmsg->request == VHOST_USER_ADD_MEM_REG ||
+        vmsg->request == VHOST_USER_SET_MEM_TABLE) {
+        return;
+    }
+
     for (i = 0; i < vmsg->fd_num; i++) {
         qemu_socket_set_nonblock(vmsg->fds[i]);
     }