Adds io_writev_zerocopy and io_flush_zerocopy as optional callback to
QIOChannelClass,
allowing the implementation of zerocopy writes by subclasses.
How to use them:
- Write data using qio_channel_writev_zerocopy(),
- Wait write completion with qio_channel_flush_zerocopy().
Notes:
As some zerocopy implementations work asynchronously, it's
recommended to keep the write buffer untouched until the return of
qio_channel_flush_zerocopy(), to avoid the risk of sending an updated
buffer instead of the one at the write.
As the new callbacks are optional, if a subclass does not implement them, then:
- io_writev_zerocopy will return -1,
- io_flush_zerocopy will return 0 without changing anything.
Also, some functions like qio_channel_writev_full_all() were adapted to
receive a flag parameter. That allows shared code between zerocopy and
non-zerocopy writev.
Signed-off-by: Leonardo Bras <leob...@redhat.com>
---
include/io/channel.h | 93 ++++++++++++++++++++++++++++++++++++++------
io/channel.c | 65 +++++++++++++++++++++++++------
2 files changed, 135 insertions(+), 23 deletions(-)
diff --git a/include/io/channel.h b/include/io/channel.h
index 88988979f8..a19c09bb84 100644
--- a/include/io/channel.h
+++ b/include/io/channel.h
@@ -32,12 +32,15 @@ OBJECT_DECLARE_TYPE(QIOChannel, QIOChannelClass,
#define QIO_CHANNEL_ERR_BLOCK -2
+#define QIO_CHANNEL_WRITE_FLAG_ZEROCOPY 0x1
+
typedef enum QIOChannelFeature QIOChannelFeature;
enum QIOChannelFeature {
QIO_CHANNEL_FEATURE_FD_PASS,
QIO_CHANNEL_FEATURE_SHUTDOWN,
QIO_CHANNEL_FEATURE_LISTEN,
+ QIO_CHANNEL_FEATURE_WRITE_ZEROCOPY,
};
@@ -136,6 +139,12 @@ struct QIOChannelClass {
IOHandler *io_read,
IOHandler *io_write,
void *opaque);
+ ssize_t (*io_writev_zerocopy)(QIOChannel *ioc,
+ const struct iovec *iov,
+ size_t niov,
+ Error **errp);
+ int (*io_flush_zerocopy)(QIOChannel *ioc,
+ Error **errp);
};
/* General I/O handling functions */
@@ -321,10 +330,11 @@ int qio_channel_readv_all(QIOChannel *ioc,
/**
- * qio_channel_writev_all:
+ * qio_channel_writev_all_flags:
* @ioc: the channel object
* @iov: the array of memory regions to write data from
* @niov: the length of the @iov array
+ * @flags: write flags (QIO_CHANNEL_WRITE_FLAG_*)
* @errp: pointer to a NULL-initialized error object
*
* Write data to the IO channel, reading it from the
@@ -337,12 +347,23 @@ int qio_channel_readv_all(QIOChannel *ioc,
* to be written, yielding from the current coroutine
* if required.
*
+ * If QIO_CHANNEL_WRITE_FLAG_ZEROCOPY is passed in flags,
+ * instead of waiting for all requested data to be written,
+ * this function will wait until it's all queued for writing.
+ * In this case, if the buffer gets changed between queueing and
+ * sending, the updated buffer will be sent. If this is not a
+ * desired behavior, it's suggested to call qio_channel_flush_zerocopy()
+ * before reusing the buffer.
+ *
* Returns: 0 if all bytes were written, or -1 on error
*/
-int qio_channel_writev_all(QIOChannel *ioc,
- const struct iovec *iov,
- size_t niov,
- Error **erp);
+int qio_channel_writev_all_flags(QIOChannel *ioc,
+ const struct iovec *iov,
+ size_t niov,
+ int flags,
+ Error **errp);
+#define qio_channel_writev_all(ioc, iov, niov, errp) \
+ qio_channel_writev_all_flags(ioc, iov, niov, 0, errp)
/**
* qio_channel_readv:
@@ -831,12 +852,13 @@ int qio_channel_readv_full_all(QIOChannel *ioc,
Error **errp);
/**
- * qio_channel_writev_full_all:
+ * qio_channel_writev_full_all_flags:
* @ioc: the channel object
* @iov: the array of memory regions to write data from
* @niov: the length of the @iov array
* @fds: an array of file handles to send
* @nfds: number of file handles in @fds
+ * @flags: write flags (QIO_CHANNEL_WRITE_FLAG_*)
* @errp: pointer to a NULL-initialized error object
*
*
@@ -846,13 +868,62 @@ int qio_channel_readv_full_all(QIOChannel *ioc,
* to be written, yielding from the current coroutine
* if required.
*
+ * If QIO_CHANNEL_WRITE_FLAG_ZEROCOPY is passed in flags,
+ * instead of waiting for all requested data to be written,
+ * this function will wait until it's all queued for writing.
+ * In this case, if the buffer gets changed between queueing and
+ * sending, the updated buffer will be sent. If this is not a
+ * desired behavior, it's suggested to call qio_channel_flush_zerocopy()
+ * before reusing the buffer.
+ *
* Returns: 0 if all bytes were written, or -1 on error
*/
-int qio_channel_writev_full_all(QIOChannel *ioc,
- const struct iovec *iov,
- size_t niov,
- int *fds, size_t nfds,
- Error **errp);
+int qio_channel_writev_full_all_flags(QIOChannel *ioc,
+ const struct iovec *iov,
+ size_t niov,
+ int *fds, size_t nfds,
+ int flags, Error **errp);
+#define qio_channel_writev_full_all(ioc, iov, niov, fds, nfds, errp) \
+ qio_channel_writev_full_all_flags(ioc, iov, niov, fds, nfds, 0, errp)
+
+/**
+ * qio_channel_writev_zerocopy:
+ * @ioc: the channel object
+ * @iov: the array of memory regions to write data from
+ * @niov: the length of the @iov array
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Behaves like qio_channel_writev_full_all_flags, but may write
+ * data asynchronously while avoiding unnecessary data copy.
+ * This function may return before any data is actually written,
+ * but should queue every buffer for writing.
+ *
+ * If at some point it's necessary to wait for all data to be
+ * written, use qio_channel_flush_zerocopy().
+ *
+ * If zerocopy is not available, returns -1 and set errp.
+ */
+
+ssize_t qio_channel_writev_zerocopy(QIOChannel *ioc,
+ const struct iovec *iov,
+ size_t niov,
+ Error **errp);
+
+/**
+ * qio_channel_flush_zerocopy:
+ * @ioc: the channel object
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Will block until every packet queued with
+ * qio_channel_writev_zerocopy() is sent, or return
+ * in case of any error.
+ *
+ * Returns -1 if any error is found, 0 otherwise.
+ * If not implemented, acts as a no-op, and returns 0.
+ */
+
+int qio_channel_flush_zerocopy(QIOChannel *ioc,
+ Error **errp);
#endif /* QIO_CHANNEL_H */
diff --git a/io/channel.c b/io/channel.c
index e8b019dc36..009da9b772 100644
--- a/io/channel.c
+++ b/io/channel.c
@@ -212,19 +212,21 @@ int qio_channel_readv_full_all(QIOChannel *ioc,
return ret;
}
-int qio_channel_writev_all(QIOChannel *ioc,
- const struct iovec *iov,
- size_t niov,
- Error **errp)
+int qio_channel_writev_all_flags(QIOChannel *ioc,
+ const struct iovec *iov,
+ size_t niov,
+ int flags,
+ Error **errp)
{
- return qio_channel_writev_full_all(ioc, iov, niov, NULL, 0, errp);
+ return qio_channel_writev_full_all_flags(ioc, iov, niov, NULL, 0, flags,
+ errp);
}
-int qio_channel_writev_full_all(QIOChannel *ioc,
- const struct iovec *iov,
- size_t niov,
- int *fds, size_t nfds,
- Error **errp)
+int qio_channel_writev_full_all_flags(QIOChannel *ioc,
+ const struct iovec *iov,
+ size_t niov,
+ int *fds, size_t nfds,
+ int flags, Error **errp)
{
int ret = -1;
struct iovec *local_iov = g_new(struct iovec, niov);
@@ -237,8 +239,15 @@ int qio_channel_writev_full_all(QIOChannel *ioc,
while (nlocal_iov > 0) {
ssize_t len;
- len = qio_channel_writev_full(ioc, local_iov, nlocal_iov, fds, nfds,
- errp);
+
+ if (flags & QIO_CHANNEL_WRITE_FLAG_ZEROCOPY) {
+ assert(fds == NULL && nfds == 0);
+ len = qio_channel_writev_zerocopy(ioc, local_iov, nlocal_iov,
errp);
+ } else {
+ len = qio_channel_writev_full(ioc, local_iov, nlocal_iov, fds,
nfds,
+ errp);
+ }
+
if (len == QIO_CHANNEL_ERR_BLOCK) {
if (qemu_in_coroutine()) {
qio_channel_yield(ioc, G_IO_OUT);
@@ -474,6 +483,38 @@ off_t qio_channel_io_seek(QIOChannel *ioc,
}
+ssize_t qio_channel_writev_zerocopy(QIOChannel *ioc,
+ const struct iovec *iov,
+ size_t niov,
+ Error **errp)
+{
+ QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
+
+ if (!klass->io_writev_zerocopy ||
+ !qio_channel_has_feature(ioc, QIO_CHANNEL_FEATURE_WRITE_ZEROCOPY)) {
+ error_setg_errno(errp, EINVAL,
+ "Channel does not support zerocopy writev");
+ return -1;
+ }
+
+ return klass->io_writev_zerocopy(ioc, iov, niov, errp);
+}
+
+
+int qio_channel_flush_zerocopy(QIOChannel *ioc,
+ Error **errp)
+{
+ QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
+
+ if (!klass->io_flush_zerocopy ||
+ !qio_channel_has_feature(ioc, QIO_CHANNEL_FEATURE_WRITE_ZEROCOPY)) {
+ return 0;
+ }
+
+ return klass->io_flush_zerocopy(ioc, errp);
+}
+
+
static void qio_channel_restart_read(void *opaque)
{
QIOChannel *ioc = opaque;
--
2.33.1
