[Qemu-devel] [PATCH] block: Introduce "null" driver

[Fam Zheng]

This is an analogue to Linux null_blk. It can be used for testing block
device emulation and general block layer functionalities such as
coroutines and throttling, where disk IO is not necessary or wanted.

Signed-off-by: Fam Zheng <address@hidden>
---
 block/Makefile.objs |   1 +
 block/null.c        | 172 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 173 insertions(+)
 create mode 100644 block/null.c

diff --git a/block/Makefile.objs b/block/Makefile.objs
index 858d2b3..087e281 100644
--- a/block/Makefile.objs
+++ b/block/Makefile.objs
@@ -9,6 +9,7 @@ block-obj-y += snapshot.o qapi.o
 block-obj-$(CONFIG_WIN32) += raw-win32.o win32-aio.o
 block-obj-$(CONFIG_POSIX) += raw-posix.o
 block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
+block-obj-y += null.o
 
 ifeq ($(CONFIG_POSIX),y)
 block-obj-y += nbd.o nbd-client.o sheepdog.o
diff --git a/block/null.c b/block/null.c
new file mode 100644
index 0000000..d93a24d
--- /dev/null
+++ b/block/null.c
@@ -0,0 +1,172 @@
+/*
+ * Null block driver
+ *
+ * Authors:
+ *  Fam Zheng <address@hidden>
+ *
+ * Copyright (C) 2014 Red Hat, Inc.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "block/block_int.h"
+
+typedef struct {
+    int64_t length;
+} BDRVNullState;
+
+static QemuOptsList runtime_opts = {
+    .name = "null",
+    .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
+    .desc = {
+        {
+            .name = "filename",
+            .type = QEMU_OPT_STRING,
+            .help = "",
+        },
+        { /* end of list */ }
+    },
+};
+
+static int null_file_open(BlockDriverState *bs, QDict *options, int flags,
+                          Error **errp)
+{
+    QemuOpts *opts;
+
+    opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
+    qemu_opts_absorb_qdict(opts, options, &error_abort);
+    qemu_opts_del(opts);
+    return 0;
+}
+
+static void null_close(BlockDriverState *bs)
+{
+}
+
+static int64_t null_getlength(BlockDriverState *bs)
+{
+    /* Size is not very relevant, let's report 1G for now */
+    return 1 << 30;
+}
+
+#ifdef NULL_COROUTINE
+static coroutine_fn int null_co_read(BlockDriverState *bs, int64_t sector_num,
+                                     uint8_t *buf, int nb_sectors)
+{
+    return 0;
+}
+
+static coroutine_fn int null_co_write(BlockDriverState *bs, int64_t sector_num,
+                                      const uint8_t *buf, int nb_sectors)
+{
+    return 0;
+}
+
+static coroutine_fn int null_co_flush(BlockDriverState *bs)
+{
+    return 0;
+}
+#else
+
+typedef struct {
+    BlockDriverAIOCB common;
+    QEMUBH *bh;
+} NullAIOCB;
+
+typedef struct BlkdebugSuspendedReq {
+    Coroutine *co;
+    char *tag;
+    QLIST_ENTRY(BlkdebugSuspendedReq) next;
+} BlkdebugSuspendedReq;
+
+static void null_aio_cancel(BlockDriverAIOCB *blockacb);
+
+static const AIOCBInfo null_aiocb_info = {
+    .aiocb_size = sizeof(NullAIOCB),
+    .cancel     = null_aio_cancel,
+};
+
+static void null_bh_cb(void *opaque)
+{
+    NullAIOCB *acb = opaque;
+    acb->common.cb(acb->common.opaque, 0);
+    qemu_bh_delete(acb->bh);
+    qemu_aio_release(acb);
+}
+
+static BlockDriverAIOCB *null_aio_readv(BlockDriverState *bs,
+                                        int64_t sector_num, QEMUIOVector *qiov,
+                                        int nb_sectors,
+                                        BlockDriverCompletionFunc *cb,
+                                        void *opaque)
+{
+    NullAIOCB *acb;
+
+    acb = qemu_aio_get(&null_aiocb_info, bs, cb, opaque);
+    acb->bh = aio_bh_new(bdrv_get_aio_context(bs), null_bh_cb, acb);
+    qemu_bh_schedule(acb->bh);
+    return &acb->common;
+}
+
+static BlockDriverAIOCB *null_aio_writev(BlockDriverState *bs,
+                                         int64_t sector_num, QEMUIOVector 
*qiov,
+                                         int nb_sectors,
+                                         BlockDriverCompletionFunc *cb,
+                                         void *opaque)
+{
+    NullAIOCB *acb;
+
+    acb = qemu_aio_get(&null_aiocb_info, bs, cb, opaque);
+    acb->bh = aio_bh_new(bdrv_get_aio_context(bs), null_bh_cb, acb);
+    qemu_bh_schedule(acb->bh);
+    return &acb->common;
+}
+
+static BlockDriverAIOCB *null_aio_flush(BlockDriverState *bs,
+                                        BlockDriverCompletionFunc *cb,
+                                        void *opaque)
+{
+    NullAIOCB *acb;
+
+    acb = qemu_aio_get(&null_aiocb_info, bs, cb, opaque);
+    acb->bh = aio_bh_new(bdrv_get_aio_context(bs), null_bh_cb, acb);
+    qemu_bh_schedule(acb->bh);
+    return &acb->common;
+}
+
+static void null_aio_cancel(BlockDriverAIOCB *blockacb)
+{
+    NullAIOCB *acb = container_of(blockacb, NullAIOCB, common);
+    qemu_bh_delete(acb->bh);
+    qemu_aio_release(acb);
+}
+
+#endif
+
+static BlockDriver bdrv_null = {
+    .format_name            = "null",
+    .protocol_name          = "null",
+    .instance_size          = sizeof(BDRVNullState),
+
+    .bdrv_file_open         = null_file_open,
+    .bdrv_close             = null_close,
+    .bdrv_getlength         = null_getlength,
+
+#ifdef NULL_COROUTINE
+    .bdrv_read              = null_co_read,
+    .bdrv_write             = null_co_write,
+    .bdrv_co_flush_to_disk  = null_co_flush,
+#else
+    .bdrv_aio_readv         = null_aio_readv,
+    .bdrv_aio_writev        = null_aio_writev,
+    .bdrv_aio_flush         = null_aio_flush,
+#endif
+};
+
+static void bdrv_null_init(void)
+{
+    bdrv_register(&bdrv_null);
+}
+
+block_init(bdrv_null_init);
-- 
2.1.0