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Fri, 12 Nov 2021 10:54:38 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.12]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 24B18607CB; Fri, 12 Nov 2021 10:54:20 +0000 (UTC) Date: Fri, 12 Nov 2021 10:54:18 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Leonardo Bras Subject: Re: [PATCH v5 3/6] QIOChannelSocket: Implement io_writev_zerocopy & io_flush_zerocopy for CONFIG_LINUX Message-ID: References: <20211112051040.923746-1-leobras@redhat.com> <20211112051040.923746-4-leobras@redhat.com> MIME-Version: 1.0 In-Reply-To: <20211112051040.923746-4-leobras@redhat.com> User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.699, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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?= Cc: qemu-devel@nongnu.org, Markus Armbruster , Eric Blake , "Dr. David Alan Gilbert" , Juan Quintela Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Nov 12, 2021 at 02:10:38AM -0300, Leonardo Bras wrote: > For CONFIG_LINUX, implement the new optional callbacks io_write_zerocopy and > io_flush_zerocopy on QIOChannelSocket, but enables it only when MSG_ZEROCOPY > feature is available in the host kernel, which is checked on > qio_channel_socket_connect_sync() > > qio_channel_socket_flush_zerocopy() was implemented by counting how many times > sendmsg(...,MSG_ZEROCOPY) was successfully called, and then reading the > socket's error queue, in order to find how many of them finished sending. > Flush will loop until those counters are the same, or until some error occurs. > > A new function qio_channel_socket_poll() was also created in order to avoid > busy-looping recvmsg() in qio_channel_socket_flush_zerocopy() while waiting for > updates in socket's error queue. > > Notes on using writev_zerocopy(): > 1: Buffer > - As MSG_ZEROCOPY tells the kernel to use the same user buffer to avoid copying, > some caution is necessary to avoid overwriting any buffer before it's sent. > If something like this happen, a newer version of the buffer may be sent instead. > - If this is a problem, it's recommended to call flush_zerocopy() before freeing > or re-using the buffer. > > 2: Locked memory > - When using MSG_ZERCOCOPY, the buffer memory will be locked after queued, and > unlocked after it's sent. > - Depending on the size of each buffer, and how often it's sent, it may require > a larger amount of locked memory than usually available to non-root user. > - If the required amount of locked memory is not available, writev_zerocopy > will return an error, which can abort an operation like migration, > - Because of this, when an user code wants to add zerocopy as a feature, it > requires a mechanism to disable it, so it can still be accessible to less > privileged users. > > Signed-off-by: Leonardo Bras > --- > include/io/channel-socket.h | 2 + > include/io/channel.h | 1 + > io/channel-socket.c | 150 +++++++++++++++++++++++++++++++++++- > 3 files changed, 150 insertions(+), 3 deletions(-) > > diff --git a/include/io/channel-socket.h b/include/io/channel-socket.h > index e747e63514..81d04baa4c 100644 > --- a/include/io/channel-socket.h > +++ b/include/io/channel-socket.h > @@ -47,6 +47,8 @@ struct QIOChannelSocket { > socklen_t localAddrLen; > struct sockaddr_storage remoteAddr; > socklen_t remoteAddrLen; > + ssize_t zerocopy_queued; > + ssize_t zerocopy_sent; > }; > > > diff --git a/include/io/channel.h b/include/io/channel.h > index a19c09bb84..051fff4197 100644 > --- a/include/io/channel.h > +++ b/include/io/channel.h > @@ -31,6 +31,7 @@ OBJECT_DECLARE_TYPE(QIOChannel, QIOChannelClass, > > > #define QIO_CHANNEL_ERR_BLOCK -2 > +#define QIO_CHANNEL_ERR_NOBUFS -3 > > #define QIO_CHANNEL_WRITE_FLAG_ZEROCOPY 0x1 > > diff --git a/io/channel-socket.c b/io/channel-socket.c > index b57a27bf91..c724b849ad 100644 > --- a/io/channel-socket.c > +++ b/io/channel-socket.c > @@ -26,6 +26,10 @@ > #include "io/channel-watch.h" > #include "trace.h" > #include "qapi/clone-visitor.h" > +#ifdef CONFIG_LINUX > +#include > +#include > +#endif > > #define SOCKET_MAX_FDS 16 > > @@ -55,6 +59,8 @@ qio_channel_socket_new(void) > > sioc = QIO_CHANNEL_SOCKET(object_new(TYPE_QIO_CHANNEL_SOCKET)); > sioc->fd = -1; > + sioc->zerocopy_queued = 0; > + sioc->zerocopy_sent = 0; > > ioc = QIO_CHANNEL(sioc); > qio_channel_set_feature(ioc, QIO_CHANNEL_FEATURE_SHUTDOWN); > @@ -140,6 +146,7 @@ int qio_channel_socket_connect_sync(QIOChannelSocket *ioc, > Error **errp) > { > int fd; > + int ret, v = 1; > > trace_qio_channel_socket_connect_sync(ioc, addr); > fd = socket_connect(addr, errp); > @@ -154,6 +161,15 @@ int qio_channel_socket_connect_sync(QIOChannelSocket *ioc, > return -1; > } > > +#ifdef CONFIG_LINUX > + ret = qemu_setsockopt(fd, SOL_SOCKET, SO_ZEROCOPY, &v, sizeof(v)); > + if (ret == 0) { > + /* Zerocopy available on host */ > + qio_channel_set_feature(QIO_CHANNEL(ioc), > + QIO_CHANNEL_FEATURE_WRITE_ZEROCOPY); > + } > +#endif > + > return 0; > } > > @@ -561,12 +577,15 @@ static ssize_t qio_channel_socket_writev_flags(QIOChannel *ioc, > retry: > ret = sendmsg(sioc->fd, &msg, flags); > if (ret <= 0) { > - if (errno == EAGAIN) { > + switch (errno) { > + case EAGAIN: > return QIO_CHANNEL_ERR_BLOCK; > - } > - if (errno == EINTR) { > + case EINTR: > goto retry; > + case ENOBUFS: > + return QIO_CHANNEL_ERR_NOBUFS; Why does ENOBUFS need handling separately instead of letting the error_setg_errno below handle it ? The caller immediately invokes error_setg_errno() again, just with different error message. No code in this series ever looks at QIO_CHANNEL_ERR_NOBUFS either, so we don't even need that special error return code added AFAICT ? > } > + > error_setg_errno(errp, errno, > "Unable to write to socket"); > return -1; > @@ -670,6 +689,127 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc, > } > #endif /* WIN32 */ > > + > +#ifdef CONFIG_LINUX > + > +static int qio_channel_socket_poll(QIOChannelSocket *sioc, bool zerocopy, > + Error **errp) There's only one caller and it always passes zerocopy=true, so this parmeter looks pointless. > +{ > + struct pollfd pfd; > + int ret; > + > + pfd.fd = sioc->fd; > + pfd.events = 0; > + > + retry: > + ret = poll(&pfd, 1, -1); > + if (ret < 0) { > + switch (errno) { > + case EAGAIN: > + case EINTR: > + goto retry; > + default: > + error_setg_errno(errp, errno, > + "Poll error"); > + return ret; return -1; > + } > + } > + > + if (pfd.revents & (POLLHUP | POLLNVAL)) { > + error_setg(errp, "Poll error: Invalid or disconnected fd"); > + return -1; > + } > + > + if (!zerocopy && (pfd.revents & POLLERR)) { > + error_setg(errp, "Poll error: Errors present in errqueue"); > + return -1; > + } > + > + return ret; return 0; > +} > + > +static ssize_t qio_channel_socket_writev_zerocopy(QIOChannel *ioc, > + const struct iovec *iov, > + size_t niov, > + Error **errp) > +{ > + QIOChannelSocket *sioc = QIO_CHANNEL_SOCKET(ioc); > + ssize_t ret; > + > + ret = qio_channel_socket_writev_flags(ioc, iov, niov, NULL, 0, > + MSG_ZEROCOPY, errp); > + if (ret == QIO_CHANNEL_ERR_NOBUFS) { > + error_setg_errno(errp, errno, > + "Process can't lock enough memory for using MSG_ZEROCOPY"); This should not be touching errno - the method should be setting the errp directly, not leaving it to the caller. > + return -1; > + } > + > + sioc->zerocopy_queued++; if (ret > 0) sio->zerocopy_queued++ since the kernel doesn't increase the counter if the data sent was zero length. A caller shouldn't be passing us a zero length iov data element, but it is wise to be cautious > + return ret; > +} > + > +static int qio_channel_socket_flush_zerocopy(QIOChannel *ioc, > + Error **errp) > +{ > + QIOChannelSocket *sioc = QIO_CHANNEL_SOCKET(ioc); > + struct msghdr msg = {}; > + struct sock_extended_err *serr; > + struct cmsghdr *cm; > + char control[CMSG_SPACE(sizeof(*serr))]; > + int ret; Add int rv = 0; > + > + msg.msg_control = control; > + msg.msg_controllen = sizeof(control); > + memset(control, 0, sizeof(control)); > + > + while (sioc->zerocopy_sent < sioc->zerocopy_queued) { > + ret = recvmsg(sioc->fd, &msg, MSG_ERRQUEUE); > + if (ret < 0) { > + switch (errno) { > + case EAGAIN: > + /* Nothing on errqueue, wait until something is available */ > + ret = qio_channel_socket_poll(sioc, true, errp); > + if (ret < 0) { > + return -1; > + } > + continue; > + case EINTR: > + continue; > + default: > + error_setg_errno(errp, errno, > + "Unable to read errqueue"); > + return -1; > + } > + } > + > + cm = CMSG_FIRSTHDR(&msg); > + if (cm->cmsg_level != SOL_IP && > + cm->cmsg_type != IP_RECVERR) { > + error_setg_errno(errp, EPROTOTYPE, > + "Wrong cmsg in errqueue"); > + return -1; > + } > + > + serr = (void *) CMSG_DATA(cm); > + if (serr->ee_errno != SO_EE_ORIGIN_NONE) { > + error_setg_errno(errp, serr->ee_errno, > + "Error on socket"); > + return -1; > + } > + if (serr->ee_origin != SO_EE_ORIGIN_ZEROCOPY) { > + error_setg_errno(errp, serr->ee_origin, > + "Error not from zerocopy"); > + return -1; > + } > + > + /* No errors, count successfully finished sendmsg()*/ > + sioc->zerocopy_sent += serr->ee_data - serr->ee_info + 1; Here add if (ee_code == SO_EE_CODE_ZEROCOPY_COPIED) rv = 1; > + } > + return 0; return rv; > +} 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 :|