[Qemu-devel] [PATCH] libvhost-user: Send messages with no data

[Qemu-devel] [PATCH] libvhost-user: Send messages with no data

[Dr. David Alan Gilbert (git)]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

The response to a VHOST_USER_POSTCOPY_ADVISE contains a fd but doesn't
actually contain any data.   FIx vu_message_write so that it doesn't
do a 0-byte write() call, since this was ending up with rc=0
that was confusing the error handling code.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 contrib/libvhost-user/libvhost-user.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
index beeed0c43f..54e643d871 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -323,13 +323,15 @@ vu_message_write(VuDev *dev, int conn_fd, VhostUserMsg *vmsg)
         rc = sendmsg(conn_fd, &msg, 0);
     } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
 
-    do {
-        if (vmsg->data) {
-            rc = write(conn_fd, vmsg->data, vmsg->size);
-        } else {
-            rc = write(conn_fd, p + VHOST_USER_HDR_SIZE, vmsg->size);
-        }
-    } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
+    if (vmsg->size) {
+        do {
+            if (vmsg->data) {
+                rc = write(conn_fd, vmsg->data, vmsg->size);
+            } else {
+                rc = write(conn_fd, p + VHOST_USER_HDR_SIZE, vmsg->size);
+            }
+        } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
+    }
 
     if (rc <= 0) {
         vu_panic(dev, "Error while writing: %s", strerror(errno));
-- 
2.17.0

Re: [Qemu-devel] [PATCH] libvhost-user: Send messages with no data

[Marc-André Lureau]

On Fri, May 4, 2018 at 11:53 AM, Dr. David Alan Gilbert (git)
<dgilbert@redhat.com> wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
>
> The response to a VHOST_USER_POSTCOPY_ADVISE contains a fd but doesn't
> actually contain any data.   FIx vu_message_write so that it doesn't
> do a 0-byte write() call, since this was ending up with rc=0
> that was confusing the error handling code.
>
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>


> ---
>  contrib/libvhost-user/libvhost-user.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
> index beeed0c43f..54e643d871 100644
> --- a/contrib/libvhost-user/libvhost-user.c
> +++ b/contrib/libvhost-user/libvhost-user.c
> @@ -323,13 +323,15 @@ vu_message_write(VuDev *dev, int conn_fd, VhostUserMsg *vmsg)
>          rc = sendmsg(conn_fd, &msg, 0);
>      } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
>
> -    do {
> -        if (vmsg->data) {
> -            rc = write(conn_fd, vmsg->data, vmsg->size);
> -        } else {
> -            rc = write(conn_fd, p + VHOST_USER_HDR_SIZE, vmsg->size);
> -        }
> -    } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
> +    if (vmsg->size) {
> +        do {
> +            if (vmsg->data) {
> +                rc = write(conn_fd, vmsg->data, vmsg->size);
> +            } else {
> +                rc = write(conn_fd, p + VHOST_USER_HDR_SIZE, vmsg->size);
> +            }
> +        } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
> +    }
>
>      if (rc <= 0) {
>          vu_panic(dev, "Error while writing: %s", strerror(errno));
> --
> 2.17.0
>
>



-- 
Marc-André Lureau

Re: [Qemu-devel] [PATCH] libvhost-user: Send messages with no data

[Eric Blake]

On 05/04/2018 04:53 AM, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> The response to a VHOST_USER_POSTCOPY_ADVISE contains a fd but doesn't

s/a fd/an fd/ ? Depends on whether you pronounce it "eff-dee" or 
"file-descriptor".

> actually contain any data.   FIx vu_message_write so that it doesn't

s/FIx/Fix/

> do a 0-byte write() call, since this was ending up with rc=0
> that was confusing the error handling code.
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>   contrib/libvhost-user/libvhost-user.c | 16 +++++++++-------
>   1 file changed, 9 insertions(+), 7 deletions(-)
> 
-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org