[PATCH v3 1/2] QIOChannelSocket: Introduce assert and reduce ifdefs to improve readability

[PATCH v3 1/2] QIOChannelSocket: Introduce assert and reduce ifdefs to improve readability

[Leonardo Bras]

During implementation of MSG_ZEROCOPY feature, a lot of #ifdefs were
introduced, particularly at qio_channel_socket_writev().

Rewrite some of those changes so it's easier to read.

Also, introduce an assert to help detect incorrect zero-copy usage is when
it's disabled on build.

Signed-off-by: Leonardo Bras <leobras@redhat.com>
---
 io/channel-socket.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/io/channel-socket.c b/io/channel-socket.c
index dc9c165de1..cdce7b0b45 100644
--- a/io/channel-socket.c
+++ b/io/channel-socket.c
@@ -578,11 +578,13 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc,
         memcpy(CMSG_DATA(cmsg), fds, fdsize);
     }
 
-#ifdef QEMU_MSG_ZEROCOPY
     if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) {
+#ifdef QEMU_MSG_ZEROCOPY
         sflags = MSG_ZEROCOPY;
-    }
+#else
+        g_assert_unreachable();
 #endif
+    }
 
  retry:
     ret = sendmsg(sioc->fd, &msg, sflags);
@@ -592,15 +594,13 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc,
             return QIO_CHANNEL_ERR_BLOCK;
         case EINTR:
             goto retry;
-#ifdef QEMU_MSG_ZEROCOPY
         case ENOBUFS:
-            if (sflags & MSG_ZEROCOPY) {
+            if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) {
                 error_setg_errno(errp, errno,
                                  "Process can't lock enough memory for using MSG_ZEROCOPY");
                 return -1;
             }
             break;
-#endif
         }
 
         error_setg_errno(errp, errno,
-- 
2.36.1

[PATCH v3 2/2] QIOChannelSocket: Fix zero-copy send so socket flush works

[Leonardo Bras]

Somewhere between v6 and v7 the of the zero-copy-send patchset a crucial
part of the flushing mechanism got missing: incrementing zero_copy_queued.

Without that, the flushing interface becomes a no-op, and there is no
guarantee the buffer is really sent.

This can go as bad as causing a corruption in RAM during migration.

Fixes: 2bc58ffc2926 ("QIOChannelSocket: Implement io_writev zero copy flag & io_flush for CONFIG_LINUX")
Reported-by: 徐闯 <xuchuangxclwt@bytedance.com>
Signed-off-by: Leonardo Bras <leobras@redhat.com>
---
 io/channel-socket.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/io/channel-socket.c b/io/channel-socket.c
index cdce7b0b45..f31dd189a5 100644
--- a/io/channel-socket.c
+++ b/io/channel-socket.c
@@ -607,6 +607,11 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc,
                          "Unable to write to socket");
         return -1;
     }
+
+    if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) {
+        sioc->zero_copy_queued++;
+    }
+
     return ret;
 }
 #else /* WIN32 */
-- 
2.36.1

Re: [PATCH v3 1/2] QIOChannelSocket: Introduce assert and reduce ifdefs to improve readability

[Daniel P. Berrangé]

On Tue, Jun 14, 2022 at 02:17:25AM -0300, Leonardo Bras wrote:
> During implementation of MSG_ZEROCOPY feature, a lot of #ifdefs were
> introduced, particularly at qio_channel_socket_writev().
> 
> Rewrite some of those changes so it's easier to read.
> 
> Also, introduce an assert to help detect incorrect zero-copy usage is when
> it's disabled on build.
> 
> Signed-off-by: Leonardo Bras <leobras@redhat.com>
> ---
>  io/channel-socket.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/io/channel-socket.c b/io/channel-socket.c
> index dc9c165de1..cdce7b0b45 100644
> --- a/io/channel-socket.c
> +++ b/io/channel-socket.c
> @@ -578,11 +578,13 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc,
>          memcpy(CMSG_DATA(cmsg), fds, fdsize);
>      }
>  
> -#ifdef QEMU_MSG_ZEROCOPY
>      if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) {
> +#ifdef QEMU_MSG_ZEROCOPY
>          sflags = MSG_ZEROCOPY;
> -    }
> +#else

I would just add a comment:

         /* We expect QIOChannel class entry point to have
	    blocked this code path already */

> +        g_assert_unreachable();
>  #endif
> +    }
>  
>   retry:
>      ret = sendmsg(sioc->fd, &msg, sflags);
> @@ -592,15 +594,13 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc,
>              return QIO_CHANNEL_ERR_BLOCK;
>          case EINTR:
>              goto retry;
> -#ifdef QEMU_MSG_ZEROCOPY
>          case ENOBUFS:
> -            if (sflags & MSG_ZEROCOPY) {
> +            if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) {
>                  error_setg_errno(errp, errno,
>                                   "Process can't lock enough memory for using MSG_ZEROCOPY");
>                  return -1;
>              }
>              break;
> -#endif
>          }
>  
>          error_setg_errno(errp, errno,

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


With regards,
Daniel
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Re: [PATCH v3 2/2] QIOChannelSocket: Fix zero-copy send so socket flush works

[Daniel P. Berrangé]

On Tue, Jun 14, 2022 at 02:17:26AM -0300, Leonardo Bras wrote:
> Somewhere between v6 and v7 the of the zero-copy-send patchset a crucial
> part of the flushing mechanism got missing: incrementing zero_copy_queued.
> 
> Without that, the flushing interface becomes a no-op, and there is no
> guarantee the buffer is really sent.
> 
> This can go as bad as causing a corruption in RAM during migration.
> 
> Fixes: 2bc58ffc2926 ("QIOChannelSocket: Implement io_writev zero copy flag & io_flush for CONFIG_LINUX")
> Reported-by: 徐闯 <xuchuangxclwt@bytedance.com>
> Signed-off-by: Leonardo Bras <leobras@redhat.com>
> ---
>  io/channel-socket.c | 5 +++++
>  1 file changed, 5 insertions(+)

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


With regards,
Daniel
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