[Qemu-devel] [PATCH v2 4/6] raw-posix: Switch to bdrv_co_* interfaces

[Kevin Wolf <kwolf@redhat.com>]

In order to use the modern byte-based .bdrv_co_preadv/pwritev()
interface, this patch switches raw-posix to coroutine-based interfaces
as a first step. In terms of semantics and performance, it doesn't make
a difference with the existing code whether we go from a coroutine to a
callback-based interface already in block/io.c or only in linux-aio.c

As there have been concerns in the past that this change may be a step
in the wrong direction with respect to a possible AIO fast path, the
old callback-based interface for linux-aio is left around and can be
reactivated when a fast path (e.g. directly from virtio-blk dataplane,
bypassing the whole block layer) is implemented.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/linux-aio.c | 87 +++++++++++++++++++++++++++++++++++++++++--------------
 block/raw-aio.h   |  4 +++
 block/raw-posix.c | 59 +++++++++++++++++--------------------
 3 files changed, 96 insertions(+), 54 deletions(-)

diff --git a/block/linux-aio.c b/block/linux-aio.c
index 294b2bf..74d9b33 100644
--- a/block/linux-aio.c
+++ b/block/linux-aio.c
@@ -11,8 +11,10 @@
 #include "qemu-common.h"
 #include "block/aio.h"
 #include "qemu/queue.h"
+#include "block/block.h"
 #include "block/raw-aio.h"
 #include "qemu/event_notifier.h"
+#include "qemu/coroutine.h"
 
 #include <libaio.h>
 
@@ -30,6 +32,7 @@
 
 struct qemu_laiocb {
     BlockAIOCB common;
+    Coroutine *co;
     LinuxAioState *ctx;
     struct iocb iocb;
     ssize_t ret;
@@ -88,9 +91,14 @@ static void qemu_laio_process_completion(struct qemu_laiocb *laiocb)
             }
         }
     }
-    laiocb->common.cb(laiocb->common.opaque, ret);
 
-    qemu_aio_unref(laiocb);
+    laiocb->ret = ret;
+    if (laiocb->co) {
+        qemu_coroutine_enter(laiocb->co, NULL);
+    } else {
+        laiocb->common.cb(laiocb->common.opaque, ret);
+        qemu_aio_unref(laiocb);
+    }
 }
 
 /* The completion BH fetches completed I/O requests and invokes their
@@ -232,22 +240,12 @@ void laio_io_unplug(BlockDriverState *bs, LinuxAioState *s)
     }
 }
 
-BlockAIOCB *laio_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
-        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
-        BlockCompletionFunc *cb, void *opaque, int type)
+static int laio_do_submit(int fd, struct qemu_laiocb *laiocb, off_t offset,
+                          int type)
 {
-    struct qemu_laiocb *laiocb;
-    struct iocb *iocbs;
-    off_t offset = sector_num * 512;
-
-    laiocb = qemu_aio_get(&laio_aiocb_info, bs, cb, opaque);
-    laiocb->nbytes = nb_sectors * 512;
-    laiocb->ctx = s;
-    laiocb->ret = -EINPROGRESS;
-    laiocb->is_read = (type == QEMU_AIO_READ);
-    laiocb->qiov = qiov;
-
-    iocbs = &laiocb->iocb;
+    LinuxAioState *s = laiocb->ctx;
+    struct iocb *iocbs = &laiocb->iocb;
+    QEMUIOVector *qiov = laiocb->qiov;
 
     switch (type) {
     case QEMU_AIO_WRITE:
@@ -260,7 +258,7 @@ BlockAIOCB *laio_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
     default:
         fprintf(stderr, "%s: invalid AIO request type 0x%x.\n",
                         __func__, type);
-        goto out_free_aiocb;
+        return -EIO;
     }
     io_set_eventfd(&laiocb->iocb, event_notifier_get_fd(&s->e));
 
@@ -270,11 +268,56 @@ BlockAIOCB *laio_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
         (!s->io_q.plugged || s->io_q.n >= MAX_QUEUED_IO)) {
         ioq_submit(s);
     }
-    return &laiocb->common;
 
-out_free_aiocb:
-    qemu_aio_unref(laiocb);
-    return NULL;
+    return 0;
+}
+
+int coroutine_fn laio_co_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
+                                int64_t sector_num, QEMUIOVector *qiov,
+                                int nb_sectors, int type)
+{
+    off_t offset = sector_num * BDRV_SECTOR_SIZE;
+    int ret;
+
+    struct qemu_laiocb laiocb = {
+        .co         = qemu_coroutine_self(),
+        .nbytes     = nb_sectors * BDRV_SECTOR_SIZE,
+        .ctx        = s,
+        .is_read    = (type == QEMU_AIO_READ),
+        .qiov       = qiov,
+    };
+
+    ret = laio_do_submit(fd, &laiocb, offset, type);
+    if (ret < 0) {
+        return ret;
+    }
+
+    qemu_coroutine_yield();
+    return laiocb.ret;
+}
+
+BlockAIOCB *laio_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
+        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
+        BlockCompletionFunc *cb, void *opaque, int type)
+{
+    struct qemu_laiocb *laiocb;
+    off_t offset = sector_num * BDRV_SECTOR_SIZE;
+    int ret;
+
+    laiocb = qemu_aio_get(&laio_aiocb_info, bs, cb, opaque);
+    laiocb->nbytes = nb_sectors * BDRV_SECTOR_SIZE;
+    laiocb->ctx = s;
+    laiocb->ret = -EINPROGRESS;
+    laiocb->is_read = (type == QEMU_AIO_READ);
+    laiocb->qiov = qiov;
+
+    ret = laio_do_submit(fd, laiocb, offset, type);
+    if (ret < 0) {
+        qemu_aio_unref(laiocb);
+        return NULL;
+    }
+
+    return &laiocb->common;
 }
 
 void laio_detach_aio_context(LinuxAioState *s, AioContext *old_context)
diff --git a/block/raw-aio.h b/block/raw-aio.h
index 714714e..03bbfba 100644
--- a/block/raw-aio.h
+++ b/block/raw-aio.h
@@ -15,6 +15,7 @@
 #ifndef QEMU_RAW_AIO_H
 #define QEMU_RAW_AIO_H
 
+#include "qemu/coroutine.h"
 #include "qemu/iov.h"
 
 /* AIO request types */
@@ -38,6 +39,9 @@
 typedef struct LinuxAioState LinuxAioState;
 LinuxAioState *laio_init(void);
 void laio_cleanup(LinuxAioState *s);
+int coroutine_fn laio_co_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
+                                int64_t sector_num, QEMUIOVector *qiov,
+                                int nb_sectors, int type);
 BlockAIOCB *laio_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
         int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
         BlockCompletionFunc *cb, void *opaque, int type);
diff --git a/block/raw-posix.c b/block/raw-posix.c
index ce2e20f..cb98769 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -1325,14 +1325,13 @@ static BlockAIOCB *paio_submit(BlockDriverState *bs, int fd,
     return thread_pool_submit_aio(pool, aio_worker, acb, cb, opaque);
 }
 
-static BlockAIOCB *raw_aio_submit(BlockDriverState *bs,
-        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
-        BlockCompletionFunc *cb, void *opaque, int type)
+static int coroutine_fn raw_co_rw(BlockDriverState *bs, int64_t sector_num,
+                                  int nb_sectors, QEMUIOVector *qiov, int type)
 {
     BDRVRawState *s = bs->opaque;
 
     if (fd_open(bs) < 0)
-        return NULL;
+        return -EIO;
 
     /*
      * Check if the underlying device requires requests to be aligned,
@@ -1345,14 +1344,26 @@ static BlockAIOCB *raw_aio_submit(BlockDriverState *bs,
             type |= QEMU_AIO_MISALIGNED;
 #ifdef CONFIG_LINUX_AIO
         } else if (s->use_aio) {
-            return laio_submit(bs, s->aio_ctx, s->fd, sector_num, qiov,
-                               nb_sectors, cb, opaque, type);
+            return laio_co_submit(bs, s->aio_ctx, s->fd, sector_num, qiov,
+                                  nb_sectors, type);
 #endif
         }
     }
 
-    return paio_submit(bs, s->fd, sector_num, qiov, nb_sectors,
-                       cb, opaque, type);
+    return paio_submit_co(bs, s->fd, sector_num * BDRV_SECTOR_SIZE, qiov,
+                          nb_sectors * BDRV_SECTOR_SIZE, type);
+}
+
+static int coroutine_fn raw_co_readv(BlockDriverState *bs, int64_t sector_num,
+                                     int nb_sectors, QEMUIOVector *qiov)
+{
+    return raw_co_rw(bs, sector_num, nb_sectors, qiov, QEMU_AIO_READ);
+}
+
+static int coroutine_fn raw_co_writev(BlockDriverState *bs, int64_t sector_num,
+                                      int nb_sectors, QEMUIOVector *qiov)
+{
+    return raw_co_rw(bs, sector_num, nb_sectors, qiov, QEMU_AIO_WRITE);
 }
 
 static void raw_aio_plug(BlockDriverState *bs)
@@ -1375,22 +1386,6 @@ static void raw_aio_unplug(BlockDriverState *bs)
 #endif
 }
 
-static BlockAIOCB *raw_aio_readv(BlockDriverState *bs,
-        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
-        BlockCompletionFunc *cb, void *opaque)
-{
-    return raw_aio_submit(bs, sector_num, qiov, nb_sectors,
-                          cb, opaque, QEMU_AIO_READ);
-}
-
-static BlockAIOCB *raw_aio_writev(BlockDriverState *bs,
-        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
-        BlockCompletionFunc *cb, void *opaque)
-{
-    return raw_aio_submit(bs, sector_num, qiov, nb_sectors,
-                          cb, opaque, QEMU_AIO_WRITE);
-}
-
 static BlockAIOCB *raw_aio_flush(BlockDriverState *bs,
         BlockCompletionFunc *cb, void *opaque)
 {
@@ -1957,8 +1952,8 @@ BlockDriver bdrv_file = {
     .bdrv_co_get_block_status = raw_co_get_block_status,
     .bdrv_co_pwrite_zeroes = raw_co_pwrite_zeroes,
 
-    .bdrv_aio_readv = raw_aio_readv,
-    .bdrv_aio_writev = raw_aio_writev,
+    .bdrv_co_readv          = raw_co_readv,
+    .bdrv_co_writev         = raw_co_writev,
     .bdrv_aio_flush = raw_aio_flush,
     .bdrv_aio_discard = raw_aio_discard,
     .bdrv_refresh_limits = raw_refresh_limits,
@@ -2405,8 +2400,8 @@ static BlockDriver bdrv_host_device = {
     .create_opts         = &raw_create_opts,
     .bdrv_co_pwrite_zeroes = hdev_co_pwrite_zeroes,
 
-    .bdrv_aio_readv	= raw_aio_readv,
-    .bdrv_aio_writev	= raw_aio_writev,
+    .bdrv_co_readv          = raw_co_readv,
+    .bdrv_co_writev         = raw_co_writev,
     .bdrv_aio_flush	= raw_aio_flush,
     .bdrv_aio_discard   = hdev_aio_discard,
     .bdrv_refresh_limits = raw_refresh_limits,
@@ -2535,8 +2530,8 @@ static BlockDriver bdrv_host_cdrom = {
     .bdrv_create         = hdev_create,
     .create_opts         = &raw_create_opts,
 
-    .bdrv_aio_readv     = raw_aio_readv,
-    .bdrv_aio_writev    = raw_aio_writev,
+    .bdrv_co_readv          = raw_co_readv,
+    .bdrv_co_writev         = raw_co_writev,
     .bdrv_aio_flush	= raw_aio_flush,
     .bdrv_refresh_limits = raw_refresh_limits,
     .bdrv_io_plug = raw_aio_plug,
@@ -2670,8 +2665,8 @@ static BlockDriver bdrv_host_cdrom = {
     .bdrv_create        = hdev_create,
     .create_opts        = &raw_create_opts,
 
-    .bdrv_aio_readv     = raw_aio_readv,
-    .bdrv_aio_writev    = raw_aio_writev,
+    .bdrv_co_readv          = raw_co_readv,
+    .bdrv_co_writev         = raw_co_writev,
     .bdrv_aio_flush	= raw_aio_flush,
     .bdrv_refresh_limits = raw_refresh_limits,
     .bdrv_io_plug = raw_aio_plug,
-- 
1.8.3.1