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Wed, 8 Jun 2022 18:46:46 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.61]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9D0351121315; Wed, 8 Jun 2022 18:46:45 +0000 (UTC) Date: Wed, 8 Jun 2022 19:46:43 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Leonardo Bras Cc: qemu-devel@nongnu.org, Peter Xu , =?utf-8?B?5b6Q6Zev?= Subject: Re: [PATCH v1 1/1] QIOChannelSocket: Fix zero-copy send so socket flush works Message-ID: References: <20220608181808.79364-1-leobras@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220608181808.79364-1-leobras@redhat.com> User-Agent: Mutt/2.2.1 (2022-02-19) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jun 08, 2022 at 03:18:09PM -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 > garantee 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 > Signed-off-by: Leonardo Bras > --- > io/channel-socket.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/io/channel-socket.c b/io/channel-socket.c > index dc9c165de1..ca4cae930f 100644 > --- a/io/channel-socket.c > +++ b/io/channel-socket.c > @@ -554,6 +554,7 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc, > size_t fdsize = sizeof(int) * nfds; > struct cmsghdr *cmsg; > int sflags = 0; > + bool zero_copy_enabled = false; > > memset(control, 0, CMSG_SPACE(sizeof(int) * SOCKET_MAX_FDS)); > > @@ -581,6 +582,7 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc, > #ifdef QEMU_MSG_ZEROCOPY > if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) { > sflags = MSG_ZEROCOPY; > + zero_copy_enabled = true; > } > #endif > > @@ -592,21 +594,24 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc, > return QIO_CHANNEL_ERR_BLOCK; > case EINTR: > goto retry; > -#ifdef QEMU_MSG_ZEROCOPY Removing this ifdef appears incidental to the change. If this is redundant just remove it in its own patch. > case ENOBUFS: > - if (sflags & MSG_ZEROCOPY) { > + if (zero_copy_enabled) { > error_setg_errno(errp, errno, > "Process can't lock enough memory for using MSG_ZEROCOPY"); > return -1; > } > break; > -#endif > } > > error_setg_errno(errp, errno, > "Unable to write to socket"); > return -1; > } > + > + if (zero_copy_enabled) { What's wrong with if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) { sioc->zero_copy_queued++; } Introducing another local variable doesn't really add value IMHO. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|