Re: [Qemu-devel] libvhost-user: Fix the VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD check

[Boeuf, Sebastien]

>From 950c62dd450c8f6c3fc04269bbefa3a368bb39b6 Mon Sep 17 00:00:00 2001
From: Sebastien Boeuf <address@hidden>
Date: Wed, 7 Aug 2019 07:15:32 -0700
Subject: [PATCH] libvhost-user: Fix the VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD
 check

Vhost user protocol features are set as a bitmask. And the following
constant VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD value is 10 because the bit
10 indicates if the features is set or not.

The proper way to check for the presence or absence of this feature is
to shift 1 by the value of this constant and then mask it with the
actual bitmask representing the supported protocol features.

This patch aims to fix the current code as it was not doing the
shifting, but instead it was masking directly with the value of the
constant itself.

Signed-off-by: Sebastien Boeuf <address@hidden>
---
 contrib/libvhost-user/libvhost-user.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/contrib/libvhost-user/libvhost-user.c 
b/contrib/libvhost-user/libvhost-user.c
index fb61142bcc..8ff387deff 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -71,7 +71,7 @@

 /* The version of the protocol we support */
 #define VHOST_USER_VERSION 1
-#define LIBVHOST_USER_DEBUG 0
+#define LIBVHOST_USER_DEBUG 1

 #define DPRINT(...)                             \
     do {                                        \
@@ -1112,7 +1112,8 @@ bool vu_set_queue_host_notifier(VuDev *dev, VuVirtq *vq, 
int fd,

     vmsg.fd_num = fd_num;

-    if ((dev->protocol_features & VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD) == 0) {
+    if ((dev->protocol_features &
+        (1ULL << VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD)) == 0) {
         return false;
     }

@@ -2537,7 +2538,8 @@ int64_t vu_fs_cache_request(VuDev *dev, 
VhostUserSlaveRequest req, int fd,

     vmsg.fd_num = fd_num;

-    if ((dev->protocol_features & VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD) == 0) {
+    if ((dev->protocol_features &
+        (1ULL << VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD)) == 0) {
         return -EINVAL;
     }

--
2.17.1

________________________________________
From: Boeuf, Sebastien
Sent: Wednesday, August 07, 2019 9:24 AM
To: address@hidden
Cc: address@hidden; address@hidden
Subject: Re: libvhost-user: Fix the VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD check

On Wed, 2019-08-07 at 17:09 +0100, Dr. David Alan Gilbert wrote:
> * Boeuf, Sebastien (address@hidden) wrote:
> > From 0a53a81db6dd069f9b7bcdcd386845bceb3a2ac6 Mon Sep 17 00:00:00
> > 2001
> > From: Sebastien Boeuf <address@hidden>
> > Date: Wed, 7 Aug 2019 07:15:32 -0700
> > Subject: [PATCH] libvhost-user: Fix the
> > VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD
> >  check
> >
> > Vhost user protocol features are set as a bitmask. And the
> > following
> > constant VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD value is 10 because
> > the
> > bit
> > 10 indicates if the features is set or not.
> >
> > The proper way to check for the presence or absence of this feature
> > is
> > to shift 1 by the value of this constant and then mask it with the
> > actual bitmask representing the supported protocol features.
> >
> > This patch aims to fix the current code as it was not doing the
> > shifting, but instead it was masking directly with the value of the
> > constant itself.
> >
> > Signed-off-by: Sebastien Boeuf <address@hidden>
>
> Nicely spotted.
>
> Two things;
>   a) I think your mail client has wrapped the lines at some point.
>   b) I think this is why the has_feature() functione exists, so does
>      that become
>
>       if (!has_feature(dev->protocol_features,
> VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD))

Ah yes but that's because I forgot to check the patch format first :(

I'm going to update the patch.

Thanks,
Sebastien
>
> Dave
>
> > ---
> >  contrib/libvhost-user/libvhost-user.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/contrib/libvhost-user/libvhost-user.c
> > b/contrib/libvhost-
> > user/libvhost-user.c
> > index fb61142bcc..11909fb7c1 100644
> > --- a/contrib/libvhost-user/libvhost-user.c
> > +++ b/contrib/libvhost-user/libvhost-user.c
> > @@ -1112,7 +1112,7 @@ bool vu_set_queue_host_notifier(VuDev *dev,
> > VuVirtq *vq, int fd,
> >
> >      vmsg.fd_num = fd_num;
> >
> > -    if ((dev->protocol_features &
> > VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD)
> > == 0) {
> > +    if ((dev->protocol_features & (1ULL <<
> > VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD)) == 0) {
> >          return false;
> >      }
> >
> > @@ -2537,7 +2537,7 @@ int64_t vu_fs_cache_request(VuDev *dev,
> > VhostUserSlaveRequest req, int fd,
> >
> >      vmsg.fd_num = fd_num;
> >
> > -    if ((dev->protocol_features &
> > VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD)
> > == 0) {
> > +    if ((dev->protocol_features & (1ULL <<
> > VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD)) == 0) {
> >          return -EINVAL;
> >      }
> >
> > --
> > 2.17.1
>
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK