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 If something like this happen, a newer version of the buffer may be sent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 <leob...@redhat.com>
> ---
> 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 <linux/errqueue.h>
> +#include <poll.h>
> +#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
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