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From: Blue Swirl <blauwirbel@gmail.com>
Date: Tue, 24 May 2011 22:03:21 +0300
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Subject: Re: [Qemu-devel] [patch 2/7] Add blkmirror block driver
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To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: kwolf@redhat.com, Jes.Sorensen@redhat.com, dlaor@redhat.com, qemu-devel@nongnu.org, avi@redhat.com

On Tue, May 24, 2011 at 12:31 AM, Marcelo Tosatti <mtosatti@redhat.com> wro=
te:
> Mirrored writes are used by live block copy.
>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>
> Index: qemu-block-copy/block/blkmirror.c
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- /dev/null
> +++ qemu-block-copy/block/blkmirror.c
> @@ -0,0 +1,239 @@
> +/*
> + * Block driver for mirrored writes.
> + *
> + * Copyright (C) 2011 Red Hat, Inc.
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or la=
ter.
> + * See the COPYING file in the top-level directory.
> + */
> +
> +#include <stdarg.h>
> +#include "block_int.h"
> +
> +typedef struct {
> + =C2=A0 =C2=A0BlockDriverState *bs[2];
> +} BdrvMirrorState;
> +
> +/* Valid blkmirror filenames look like blkmirror:path/to/image1:path/to/=
image2 */
> +static int blkmirror_open(BlockDriverState *bs, const char *filename, in=
t flags)
> +{
> + =C2=A0 =C2=A0BdrvMirrorState *m =3D bs->opaque;
> + =C2=A0 =C2=A0int ret;
> + =C2=A0 =C2=A0char *raw, *c;
> +
> + =C2=A0 =C2=A0/* Parse the blkmirror: prefix */
> + =C2=A0 =C2=A0if (strncmp(filename, "blkmirror:", strlen("blkmirror:")))=
 {
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0return -EINVAL;
> + =C2=A0 =C2=A0}
> + =C2=A0 =C2=A0filename +=3D strlen("blkmirror:");
> +
> + =C2=A0 =C2=A0/* Parse the raw image filename */
> + =C2=A0 =C2=A0c =3D strchr(filename, ':');
> + =C2=A0 =C2=A0if (c =3D=3D NULL) {
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0return -EINVAL;
> + =C2=A0 =C2=A0}
> +
> + =C2=A0 =C2=A0raw =3D strdup(filename);
> + =C2=A0 =C2=A0raw[c - filename] =3D '\0';
> + =C2=A0 =C2=A0ret =3D bdrv_file_open(&m->bs[0], raw, flags);
> + =C2=A0 =C2=A0free(raw);
> + =C2=A0 =C2=A0if (ret < 0) {
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0return ret;
> + =C2=A0 =C2=A0}
> + =C2=A0 =C2=A0filename =3D c + 1;
> +
> + =C2=A0 =C2=A0ret =3D bdrv_file_open(&m->bs[1], filename, flags);
> + =C2=A0 =C2=A0if (ret < 0) {
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0bdrv_delete(m->bs[0]);
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0return ret;
> + =C2=A0 =C2=A0}
> +
> + =C2=A0 =C2=A0return 0;
> +}
> +
> +static void blkmirror_close(BlockDriverState *bs)
> +{
> + =C2=A0 =C2=A0BdrvMirrorState *m =3D bs->opaque;
> + =C2=A0 =C2=A0int i;
> +
> + =C2=A0 =C2=A0for (i=3D0; i<2; i++) {
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0bdrv_delete(m->bs[i]);
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0m->bs[i] =3D NULL;
> + =C2=A0 =C2=A0}
> +}
> +
> +static int blkmirror_flush(BlockDriverState *bs)
> +{
> + =C2=A0 =C2=A0BdrvMirrorState *m =3D bs->opaque;
> +
> + =C2=A0 =C2=A0bdrv_flush(m->bs[0]);
> + =C2=A0 =C2=A0bdrv_flush(m->bs[1]);
> +
> + =C2=A0 =C2=A0return 0;
> +}
> +
> +static int64_t blkmirror_getlength(BlockDriverState *bs)
> +{
> + =C2=A0 =C2=A0BdrvMirrorState *m =3D bs->opaque;
> +
> + =C2=A0 =C2=A0return bdrv_getlength(m->bs[0]);
> +}
> +
> +static BlockDriverAIOCB *blkmirror_aio_readv(BlockDriverState *bs,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 int64_t sector_num,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 QEMUIOVector *qiov,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 int nb_sectors,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 BlockDriverCompletionFunc *cb,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 void *opaque)
> +{
> + =C2=A0 =C2=A0BdrvMirrorState *m =3D bs->opaque;
> + =C2=A0 =C2=A0return bdrv_aio_readv(m->bs[0], sector_num, qiov, nb_secto=
rs, cb, opaque);
> +}
> +
> +typedef struct DupAIOCB {
> + =C2=A0 =C2=A0BlockDriverAIOCB common;
> + =C2=A0 =C2=A0int count;
> +
> + =C2=A0 =C2=A0BlockDriverCompletionFunc *cb;
> + =C2=A0 =C2=A0void *opaque;
> +
> + =C2=A0 =C2=A0BlockDriverAIOCB *src_aiocb;
> + =C2=A0 =C2=A0BlockDriverAIOCB *dest_aiocb;
> +
> + =C2=A0 =C2=A0int ret;
> +} DupAIOCB;

Usually all types are defined at the top of the file.

> +
> +static void dup_aio_cancel(BlockDriverAIOCB *blockacb)
> +{
> + =C2=A0 =C2=A0DupAIOCB *acb =3D container_of(blockacb, DupAIOCB, common)=
;
> +
> + =C2=A0 =C2=A0bdrv_aio_cancel(acb->src_aiocb);
> + =C2=A0 =C2=A0bdrv_aio_cancel(acb->dest_aiocb);
> + =C2=A0 =C2=A0qemu_aio_release(acb);
> +}
> +
> +static AIOPool dup_aio_pool =3D {
> + =C2=A0 =C2=A0.aiocb_size =C2=A0 =C2=A0 =C2=A0 =C2=A0 =3D sizeof(DupAIOC=
B),
> + =C2=A0 =C2=A0.cancel =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =3D dup_=
aio_cancel,
> +};
> +
> +static void blkmirror_aio_cb(void *opaque, int ret)
> +{
> + =C2=A0 =C2=A0DupAIOCB *dcb =3D opaque;
> +
> + =C2=A0 =C2=A0dcb->count--;
> + =C2=A0 =C2=A0assert(dcb->count >=3D 0);
> + =C2=A0 =C2=A0if (dcb->count =3D=3D 0) {
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0if (dcb->ret < 0) {
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0ret =3D dcb->ret;
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0}
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0dcb->common.cb(dcb->opaque, ret);
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0qemu_aio_release(dcb);
> + =C2=A0 =C2=A0}
> + =C2=A0 =C2=A0dcb->ret =3D ret;
> +}
> +
> +static DupAIOCB *dup_aio_get(BlockDriverState *bs,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 BlockDriverCompletionFunc *cb,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 void *opaque)
> +{
> + =C2=A0 =C2=A0DupAIOCB *dcb;
> +
> + =C2=A0 =C2=A0dcb =3D qemu_aio_get(&dup_aio_pool, bs, cb, opaque);
> + =C2=A0 =C2=A0if (!dcb)
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0return NULL;

Please use QEMU's scripts/checkpatch.pl.

> + =C2=A0 =C2=A0dcb->count =3D 2;
> + =C2=A0 =C2=A0dcb->ret =3D 0;
> + =C2=A0 =C2=A0dcb->opaque =3D opaque;
> +
> + =C2=A0 =C2=A0return dcb;
> +}
> +
> +static BlockDriverAIOCB *blkmirror_aio_writev(BlockDriverState *bs,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0int64_t sector_num,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0QEMUIOVector *qiov,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0int nb_sectors,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0BlockDriverCompletionFunc *cb,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0void *opaque)
> +{
> + =C2=A0 =C2=A0BdrvMirrorState *m =3D bs->opaque;
> + =C2=A0 =C2=A0DupAIOCB *dcb =3D dup_aio_get(bs, cb, opaque);
> +
> + =C2=A0 =C2=A0dcb->src_aiocb =3D bdrv_aio_writev(m->bs[0], sector_num, q=
iov, nb_sectors,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 &blkmirror_aio_cb, =
dcb);
> + =C2=A0 =C2=A0if (!dcb->src_aiocb) {
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0qemu_aio_release(dcb);
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0return NULL;
> + =C2=A0 =C2=A0}
> +
> + =C2=A0 =C2=A0dcb->dest_aiocb =3D bdrv_aio_writev(m->bs[1], sector_num, =
qiov, nb_sectors,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0&blkmirror_ai=
o_cb, dcb);
> + =C2=A0 =C2=A0if (!dcb->dest_aiocb) {
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0bdrv_aio_cancel(dcb->src_aiocb);
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0qemu_aio_release(dcb);
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0return NULL;
> + =C2=A0 =C2=A0}
> +
> + =C2=A0 =C2=A0return &dcb->common;
> +}
> +
> +static BlockDriverAIOCB *blkmirror_aio_flush(BlockDriverState *bs,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 BlockDriverCompletionFunc *cb,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 void *opaque)
> +{
> + =C2=A0 =C2=A0BdrvMirrorState *m =3D bs->opaque;
> + =C2=A0 =C2=A0DupAIOCB *dcb =3D dup_aio_get(bs, cb, opaque);
> +
> + =C2=A0 =C2=A0dcb->src_aiocb =3D bdrv_aio_flush(m->bs[0], &blkmirror_aio=
_cb, dcb);
> + =C2=A0 =C2=A0if (!dcb->src_aiocb) {
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0qemu_aio_release(dcb);
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0return NULL;
> + =C2=A0 =C2=A0}
> + =C2=A0 =C2=A0dcb->dest_aiocb =3D bdrv_aio_flush(m->bs[1], &blkmirror_ai=
o_cb, dcb);
> + =C2=A0 =C2=A0if (!dcb->dest_aiocb) {
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0bdrv_aio_cancel(dcb->src_aiocb);
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0qemu_aio_release(dcb);
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0return NULL;
> + =C2=A0 =C2=A0}
> +
> + =C2=A0 =C2=A0return &dcb->common;
> +}
> +
> +static int blkmirror_discard(BlockDriverState *bs, int64_t sector_num,
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 int nb_sectors)
> +{
> + =C2=A0 =C2=A0BdrvMirrorState *m =3D bs->opaque;
> + =C2=A0 =C2=A0int ret;
> +
> + =C2=A0 =C2=A0ret =3D bdrv_discard(m->bs[0], sector_num, nb_sectors);
> + =C2=A0 =C2=A0if (ret < 0) {
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0return ret;
> + =C2=A0 =C2=A0}
> +
> + =C2=A0 =C2=A0return bdrv_discard(m->bs[1], sector_num, nb_sectors);
> +}
> +
> +
> +static BlockDriver bdrv_blkmirror =3D {
> + =C2=A0 =C2=A0.format_name =C2=A0 =C2=A0 =C2=A0 =C2=A0=3D "blkmirror",
> + =C2=A0 =C2=A0.protocol_name =C2=A0 =C2=A0 =C2=A0=3D "blkmirror",
> + =C2=A0 =C2=A0.instance_size =C2=A0 =C2=A0 =C2=A0=3D sizeof(BdrvMirrorSt=
ate),
> +
> + =C2=A0 =C2=A0.bdrv_getlength =C2=A0 =C2=A0 =3D blkmirror_getlength,
> +
> + =C2=A0 =C2=A0.bdrv_file_open =C2=A0 =C2=A0 =3D blkmirror_open,
> + =C2=A0 =C2=A0.bdrv_close =C2=A0 =C2=A0 =C2=A0 =C2=A0 =3D blkmirror_clos=
e,
> + =C2=A0 =C2=A0.bdrv_flush =C2=A0 =C2=A0 =C2=A0 =C2=A0 =3D blkmirror_flus=
h,
> + =C2=A0 =C2=A0.bdrv_discard =C2=A0 =C2=A0 =C2=A0 =3D blkmirror_discard,
> +
> + =C2=A0 =C2=A0.bdrv_aio_readv =C2=A0 =C2=A0 =3D blkmirror_aio_readv,
> + =C2=A0 =C2=A0.bdrv_aio_writev =C2=A0 =C2=A0=3D blkmirror_aio_writev,
> + =C2=A0 =C2=A0.bdrv_aio_flush =C2=A0 =C2=A0 =3D blkmirror_aio_flush,
> +};
> +
> +static void bdrv_blkmirror_init(void)
> +{
> + =C2=A0 =C2=A0bdrv_register(&bdrv_blkmirror);
> +}
> +
> +block_init(bdrv_blkmirror_init);
> Index: qemu-block-copy/Makefile.objs
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- qemu-block-copy.orig/Makefile.objs
> +++ qemu-block-copy/Makefile.objs
> @@ -22,7 +22,7 @@ block-nested-y +=3D raw.o cow.o qcow.o vdi
> =C2=A0block-nested-y +=3D qcow2.o qcow2-refcount.o qcow2-cluster.o qcow2-=
snapshot.o qcow2-cache.o
> =C2=A0block-nested-y +=3D qed.o qed-gencb.o qed-l2-cache.o qed-table.o qe=
d-cluster.o
> =C2=A0block-nested-y +=3D qed-check.o
> -block-nested-y +=3D parallels.o nbd.o blkdebug.o sheepdog.o blkverify.o
> +block-nested-y +=3D parallels.o nbd.o blkdebug.o sheepdog.o blkverify.o =
blkmirror.o
> =C2=A0block-nested-$(CONFIG_WIN32) +=3D raw-win32.o
> =C2=A0block-nested-$(CONFIG_POSIX) +=3D raw-posix.o
> =C2=A0block-nested-$(CONFIG_CURL) +=3D curl.o
>
>
>
>