Re: [Qemu-devel] [PATCH 3/6] block: switch bdrv_read()/bdrv_write() to coroutines

[Zhi Yong Wu <zwu.kernel@gmail.com>]

On Thu, Oct 6, 2011 at 12:17 AM, Stefan Hajnoczi
<stefanha@linux.vnet.ibm.com> wrote:
> The bdrv_read()/bdrv_write() functions call .bdrv_read()/.bdrv_write().
> They should go through bdrv_co_do_readv() and bdrv_co_do_writev()
> instead in order to unify request processing code across sync, aio, and
> coroutine interfaces.  This is also an important step towards removing
> BlockDriverState .bdrv_read()/.bdrv_write() in the future.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
> ---
>  block.c |  112 +++++++++++++++++++++++++++++++++++----------------------------
>  1 files changed, 62 insertions(+), 50 deletions(-)
>
> diff --git a/block.c b/block.c
> index d15784e..90c29db 100644
> --- a/block.c
> +++ b/block.c
> @@ -44,6 +44,8 @@
>  #include <windows.h>
>  #endif
>
> +#define NOT_DONE 0x7fffffff /* used while emulated sync operation in progress */
> +
>  static void bdrv_dev_change_media_cb(BlockDriverState *bs, bool load);
>  static BlockDriverAIOCB *bdrv_aio_readv_em(BlockDriverState *bs,
>         int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
> @@ -74,6 +76,8 @@ static int coroutine_fn bdrv_co_writev_em(BlockDriverState *bs,
>  static int coroutine_fn bdrv_co_flush_em(BlockDriverState *bs);
>  static int coroutine_fn bdrv_co_do_readv(BlockDriverState *bs,
>     int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
> +static int coroutine_fn bdrv_co_do_writev(BlockDriverState *bs,
> +    int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
>
>  static QTAILQ_HEAD(, BlockDriverState) bdrv_states =
>     QTAILQ_HEAD_INITIALIZER(bdrv_states);
> @@ -1038,30 +1042,69 @@ static inline bool bdrv_has_async_flush(BlockDriver *drv)
>     return drv->bdrv_aio_flush != bdrv_aio_flush_em;
>  }
>
> -/* return < 0 if error. See bdrv_write() for the return codes */
> -int bdrv_read(BlockDriverState *bs, int64_t sector_num,
> -              uint8_t *buf, int nb_sectors)
> +typedef struct RwCo {
> +    BlockDriverState *bs;
> +    int64_t sector_num;
> +    int nb_sectors;
> +    QEMUIOVector *qiov;
> +    bool is_write;
> +    int ret;
> +} RwCo;
> +
> +static void coroutine_fn bdrv_rw_co_entry(void *opaque)
>  {
> -    BlockDriver *drv = bs->drv;
> +    RwCo *rwco = opaque;
>
> -    if (!drv)
> -        return -ENOMEDIUM;
> +    if (!rwco->is_write) {
> +        rwco->ret = bdrv_co_do_readv(rwco->bs, rwco->sector_num,
> +                                     rwco->nb_sectors, rwco->qiov);
> +    } else {
> +        rwco->ret = bdrv_co_do_writev(rwco->bs, rwco->sector_num,
> +                                      rwco->nb_sectors, rwco->qiov);
> +    }
> +}
>
> -    if (bdrv_has_async_rw(drv) && qemu_in_coroutine()) {
> -        QEMUIOVector qiov;
> -        struct iovec iov = {
> -            .iov_base = (void *)buf,
> -            .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
> -        };
> +/*
> + * Process a synchronous request using coroutines
> + */
> +static int bdrv_rw_co(BlockDriverState *bs, int64_t sector_num, uint8_t *buf,
> +                      int nb_sectors, bool is_write)
> +{
> +    QEMUIOVector qiov;
> +    struct iovec iov = {
> +        .iov_base = (void *)buf,
> +        .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
> +    };
> +    Coroutine *co;
> +    RwCo rwco = {
> +        .bs = bs,
> +        .sector_num = sector_num,
> +        .nb_sectors = nb_sectors,
> +        .qiov = &qiov,
> +        .is_write = is_write,
> +        .ret = NOT_DONE,
> +    };
>
> -        qemu_iovec_init_external(&qiov, &iov, 1);
> -        return bdrv_co_readv(bs, sector_num, nb_sectors, &qiov);
> -    }
> +    qemu_iovec_init_external(&qiov, &iov, 1);
>
> -    if (bdrv_check_request(bs, sector_num, nb_sectors))
> -        return -EIO;
> +    if (qemu_in_coroutine()) {
> +        /* Fast-path if already in coroutine context */
> +        bdrv_rw_co_entry(&rwco);
> +    } else {
> +        co = qemu_coroutine_create(bdrv_rw_co_entry);
> +        qemu_coroutine_enter(co, &rwco);
> +        while (rwco.ret == NOT_DONE) {
> +            qemu_aio_wait();
> +        }
> +    }
> +    return rwco.ret;
> +}
>
> -    return drv->bdrv_read(bs, sector_num, buf, nb_sectors);
> +/* return < 0 if error. See bdrv_write() for the return codes */
> +int bdrv_read(BlockDriverState *bs, int64_t sector_num,
> +              uint8_t *buf, int nb_sectors)
> +{
> +    return bdrv_rw_co(bs, sector_num, buf, nb_sectors, false);
>  }
>
>  static void set_dirty_bitmap(BlockDriverState *bs, int64_t sector_num,
> @@ -1101,36 +1144,7 @@ static void set_dirty_bitmap(BlockDriverState *bs, int64_t sector_num,
>  int bdrv_write(BlockDriverState *bs, int64_t sector_num,
>                const uint8_t *buf, int nb_sectors)
>  {
> -    BlockDriver *drv = bs->drv;
> -
> -    if (!bs->drv)
> -        return -ENOMEDIUM;
> -
> -    if (bdrv_has_async_rw(drv) && qemu_in_coroutine()) {
> -        QEMUIOVector qiov;
> -        struct iovec iov = {
> -            .iov_base = (void *)buf,
> -            .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
> -        };
> -
> -        qemu_iovec_init_external(&qiov, &iov, 1);
> -        return bdrv_co_writev(bs, sector_num, nb_sectors, &qiov);
> -    }
> -
> -    if (bs->read_only)
> -        return -EACCES;
> -    if (bdrv_check_request(bs, sector_num, nb_sectors))
> -        return -EIO;
> -
> -    if (bs->dirty_bitmap) {
> -        set_dirty_bitmap(bs, sector_num, nb_sectors, 1);
> -    }
> -
> -    if (bs->wr_highest_sector < sector_num + nb_sectors - 1) {
> -        bs->wr_highest_sector = sector_num + nb_sectors - 1;
> -    }
The above codes are removed, will it be safe?
> -
> -    return drv->bdrv_write(bs, sector_num, buf, nb_sectors);
> +    return bdrv_rw_co(bs, sector_num, (uint8_t *)buf, nb_sectors, true);
>  }
>
>  int bdrv_pread(BlockDriverState *bs, int64_t offset,
> @@ -2891,8 +2905,6 @@ static void bdrv_rw_em_cb(void *opaque, int ret)
>     *(int *)opaque = ret;
>  }
>
> -#define NOT_DONE 0x7fffffff
> -
>  static int bdrv_read_em(BlockDriverState *bs, int64_t sector_num,
>                         uint8_t *buf, int nb_sectors)
>  {
> --
> 1.7.6.3
>
>
>



-- 
Regards,

Zhi Yong Wu