[v4] vhost-user: support any POSIX system (tested on macOS, FreeBSD, OpenBSD)

[PATCH v4 04/12] vhost-user-server: do not set memory fd non-blocking

Stefano Garzarella posted 12 patches 6 months, 3 weeks ago

Diff against v2 v3 v5 v6 v7 v7 v8
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Maintainers: David Hildenbrand <david@redhat.com>, Igor Mammedov <imammedo@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, Raphael Norwitz <raphael@enfabrica.net>, Gerd Hoffmann <kraxel@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Kevin Wolf <kwolf@redhat.com>, Hanna Reitz <hreitz@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>, Eduardo Habkost <eduardo@habkost.net>, Eric Blake <eblake@redhat.com>, Markus Armbruster <armbru@redhat.com>, Coiby Xu <Coiby.Xu@gmail.com>, Laurent Vivier <lvivier@redhat.com>

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[PATCH v4 04/12] vhost-user-server: do not set memory fd non-blocking

Posted by Stefano Garzarella 6 months, 3 weeks 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).

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]);
     }
-- 
2.45.0

Re: [PATCH v4 04/12] vhost-user-server: do not set memory fd non-blocking

Posted by Daniel P. Berrangé 6 months, 3 weeks ago

On Wed, May 08, 2024 at 09:44:48AM +0200, 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).
> 
> 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(+)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


With regards,
Daniel
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