[v5] vhost-user: support any POSIX system (tested on macOS, FreeBSD, OpenBSD)

[PATCH v5 04/13] vhost-user-server: do not set memory fd non-blocking

Stefano Garzarella posted 13 patches 6 months ago

Diff against v2 v3 v4 v6 v7 v7 v8
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Maintainers: David Hildenbrand <david@redhat.com>, Igor Mammedov <imammedo@redhat.com>, Kevin Wolf <kwolf@redhat.com>, Hanna Reitz <hreitz@redhat.com>, Raphael Norwitz <raphael@enfabrica.net>, "Michael S. Tsirkin" <mst@redhat.com>, Gerd Hoffmann <kraxel@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Jason Wang <jasowang@redhat.com>, "Marc-André Lureau" <marcandre.lureau@redhat.com>, "Daniel P. Berrangé" <berrange@redhat.com>, Thomas Huth <thuth@redhat.com>, "Philippe Mathieu-Daudé" <philmd@linaro.org>, Eric Blake <eblake@redhat.com>, Markus Armbruster <armbru@redhat.com>, Eduardo Habkost <eduardo@habkost.net>, Coiby Xu <Coiby.Xu@gmail.com>, Laurent Vivier <lvivier@redhat.com>

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[PATCH v5 04/13] vhost-user-server: do not set memory fd non-blocking

Posted by Stefano Garzarella 6 months ago

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 <berrange@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
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(+)

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]);
     }
-- 
2.45.1

Re: [PATCH v5 04/13] vhost-user-server: do not set memory fd non-blocking

Posted by David Hildenbrand 6 months ago

On 23.05.24 16:55, Stefano Garzarella wrote:
> 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 <berrange@redhat.com>
> Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb