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block: Introduce "null" drivers

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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.

[Resolved conflict with Fam's async bdrv_aio_cancel() series:
1. Drop .bdrv_aio_cancel() since it is now done by block.c
2. Rename qemu_aio_release() to qemu_aio_unref()
--Stefan]

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Benoît Canet <benoit.canet@nodalink.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 1410415798-20673-2-git-send-email-famz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Fam Zheng 2014-09-11 14:09:56 +08:00 committed by Stefan Hajnoczi
parent a90d411e63
commit e819ab2277
3 changed files with 186 additions and 2 deletions
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1
block/Makefile.objs
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@ -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-$(CONFIG_LINUX_AIO) += linux-aio.o
block-obj-y += null.o
block-obj-y += nbd.o nbd-client.o sheepdog.o
block-obj-$(CONFIG_LIBISCSI) += iscsi.o

168
block/null.c Normal file
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@ -0,0 +1,168 @@
/*
* Null block driver
*
* Authors:
* Fam Zheng <famz@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_readv(BlockDriverState *bs,
int64_t sector_num, int nb_sectors,
QEMUIOVector *qiov)
{
return 0;
}
static coroutine_fn int null_co_writev(BlockDriverState *bs,
int64_t sector_num, int nb_sectors,
QEMUIOVector *qiov)
{
return 0;
}
static coroutine_fn int null_co_flush(BlockDriverState *bs)
{
return 0;
}
typedef struct {
BlockDriverAIOCB common;
QEMUBH *bh;
} NullAIOCB;
static const AIOCBInfo null_aiocb_info = {
.aiocb_size = sizeof(NullAIOCB),
};
static void null_bh_cb(void *opaque)
{
NullAIOCB *acb = opaque;
acb->common.cb(acb->common.opaque, 0);
qemu_bh_delete(acb->bh);
qemu_aio_unref(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 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_co_readv = null_co_readv,
.bdrv_co_writev = null_co_writev,
.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);

19
qapi/block-core.json
View File

@ -1151,7 +1151,8 @@
'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 +1204,18 @@
{ 'type': 'BlockdevOptionsFile',
'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',
'data': { '*size': 'int' } }
##
# @BlockdevOptionsVVFAT
#
@ -1503,7 +1516,9 @@
'vhdx': 'BlockdevOptionsGenericFormat',
'vmdk': 'BlockdevOptionsGenericCOWFormat',
'vpc': 'BlockdevOptionsGenericFormat',
'quorum': 'BlockdevOptionsQuorum'
'quorum': 'BlockdevOptionsQuorum',
'null-aio': 'BlockdevOptionsNull',
'null-co': 'BlockdevOptionsNull'
} }
##