This is an analogue to Linux null_blk. It can be used for testing or
benchmarking block device emulation and general block layer
functionalities such as coroutines and throttling, where disk IO is not
necessary or wanted.
Use null-aio:// for AIO version, and null-co:// for coroutine version.
Signed-off-by: Fam Zheng <f...@redhat.com>
Reviewed-by: Benoît Canet <benoit.ca...@nodalink.com>
---
v5: Rename "null://" to "null-aio://". (Stefan)
Add Benoit's rev-by line.
---
block/Makefile.objs | 1 +
block/null.c | 176 +++++++++++++++++++++++++++++++++++++++++++++++++++
qapi/block-core.json | 20 +++++-
3 files changed, 195 insertions(+), 2 deletions(-)
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..2d1633e
--- /dev/null
+++ b/block/null.c
@@ -0,0 +1,176 @@
+/*
+ * Null block driver
+ *
+ * Authors:
+ * Fam Zheng <f...@redhat.com>
+ *
+ * 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 = "",
+ },
+ {
+ .name = BLOCK_OPT_SIZE,
+ .type = QEMU_OPT_SIZE,
+ .help = "size of the null block",
+ },
+ { /* end of list */ }
+ },
+};
+
+static int null_file_open(BlockDriverState *bs, QDict *options, int flags,
+ Error **errp)
+{
+ QemuOpts *opts;
+ BDRVNullState *s = bs->opaque;
+
+ opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
+ qemu_opts_absorb_qdict(opts, options, &error_abort);
+ s->length =
+ qemu_opt_get_size(opts, BLOCK_OPT_SIZE, 1 << 30);
+ qemu_opts_del(opts);
+ return 0;
+}
+
+static void null_close(BlockDriverState *bs)
+{
+}
+
+static int64_t null_getlength(BlockDriverState *bs)
+{
+ BDRVNullState *s = bs->opaque;
+ return s->length;
+}
+
+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;
+}
+
+typedef struct {
+ BlockDriverAIOCB common;
+ QEMUBH *bh;
+} NullAIOCB;
+
+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 inline BlockDriverAIOCB *null_aio_common(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 BlockDriverAIOCB *null_aio_readv(BlockDriverState *bs,
+ int64_t sector_num, QEMUIOVector *qiov,
+ int nb_sectors,
+ BlockDriverCompletionFunc *cb,
+ void *opaque)
+{
+ return null_aio_common(bs, cb, opaque);
+}
+
+static BlockDriverAIOCB *null_aio_writev(BlockDriverState *bs,
+ int64_t sector_num, QEMUIOVector
*qiov,
+ int nb_sectors,
+ BlockDriverCompletionFunc *cb,
+ void *opaque)
+{
+ return null_aio_common(bs, cb, opaque);
+}
+
+static BlockDriverAIOCB *null_aio_flush(BlockDriverState *bs,
+ BlockDriverCompletionFunc *cb,
+ void *opaque)
+{
+ return null_aio_common(bs, cb, opaque);
+}
+
+static void null_aio_cancel(BlockDriverAIOCB *blockacb)
+{
+ NullAIOCB *acb = container_of(blockacb, NullAIOCB, common);
+ qemu_bh_delete(acb->bh);
+ qemu_aio_release(acb);
+}
+
+static BlockDriver bdrv_null_co = {
+ .format_name = "null-co",
+ .protocol_name = "null-co",
+ .instance_size = sizeof(BDRVNullState),
+
+ .bdrv_file_open = null_file_open,
+ .bdrv_close = null_close,
+ .bdrv_getlength = null_getlength,
+
+ .bdrv_read = null_co_read,
+ .bdrv_write = null_co_write,
+ .bdrv_co_flush_to_disk = null_co_flush,
+};
+
+static BlockDriver bdrv_null_aio = {
+ .format_name = "null-aio",
+ .protocol_name = "null-aio",
+ .instance_size = sizeof(BDRVNullState),
+
+ .bdrv_file_open = null_file_open,
+ .bdrv_close = null_close,
+ .bdrv_getlength = null_getlength,
+
+ .bdrv_aio_readv = null_aio_readv,
+ .bdrv_aio_writev = null_aio_writev,
+ .bdrv_aio_flush = null_aio_flush,
+};
+
+static void bdrv_null_init(void)
+{
+ bdrv_register(&bdrv_null_co);
+ bdrv_register(&bdrv_null_aio);
+}
+
+block_init(bdrv_null_init);
diff --git a/qapi/block-core.json b/qapi/block-core.json
index fb74c56..a63d2d9 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1150,7 +1150,8 @@
'data': [ 'archipelago', 'file', 'host_device', 'host_cdrom', 'host_floppy',
'http', 'https', 'ftp', 'ftps', 'tftp', 'vvfat', 'blkdebug',
'blkverify', 'bochs', 'cloop', 'cow', 'dmg', 'parallels', 'qcow',
- 'qcow2', 'qed', 'raw', 'vdi', 'vhdx', 'vmdk', 'vpc', 'quorum' ] }
+ 'qcow2', 'qed', 'raw', 'vdi', 'vhdx', 'vmdk', 'vpc', 'quorum',
+ 'null-aio', 'null-co' ] }
##
# @BlockdevOptionsBase
@@ -1203,6 +1204,19 @@
'data': { 'filename': 'str' } }
##
+# @BlockdevOptionsNull
+#
+# Driver specific block device options for the null backend.
+#
+# @size: #optional size of the device in bytes.
+#
+# Since: 2.2
+##
+{ 'type': 'BlockdevOptionsNull',
+ 'base': 'BlockdevOptionsFile',
+ 'data': { '*size': 'int' } }
+
+##
# @BlockdevOptionsVVFAT
#
# Driver specific block device options for the vvfat protocol.
@@ -1484,7 +1498,9 @@
'vhdx': 'BlockdevOptionsGenericFormat',
'vmdk': 'BlockdevOptionsGenericCOWFormat',
'vpc': 'BlockdevOptionsGenericFormat',
- 'quorum': 'BlockdevOptionsQuorum'
+ 'quorum': 'BlockdevOptionsQuorum',
+ 'null-aio': 'BlockdevOptionsNull',
+ 'null-co': 'BlockdevOptionsNull'
} }
##
--
2.1.0
