Re: [Qemu-block] [Qemu-devel] [PATCH 2/2] block/io: use qemu_iovec_init_buf

[Eric Blake]

On 1/29/19 8:38 AM, Vladimir Sementsov-Ogievskiy wrote:
> Use new qemu_iovec_init_buf() instead of
> qemu_iovec_init_external( ... , 1), which simplifies the code.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> ---
>  block/io.c | 89 ++++++++++++------------------------------------------
>  1 file changed, 20 insertions(+), 69 deletions(-)
> 
> diff --git a/block/io.c b/block/io.c
> index bd9d688f8b..80961910a6 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -842,17 +842,13 @@ static int bdrv_prwv_co(BdrvChild *child, int64_t 
> offset,
>  static int bdrv_rw_co(BdrvChild *child, int64_t sector_num, uint8_t *buf,
>                        int nb_sectors, bool is_write, BdrvRequestFlags flags)
>  {
> -    QEMUIOVector qiov;
> -    struct iovec iov = {
> -        .iov_base = (void *)buf,
> -        .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
> -    };
> +    QEMUIOVector qiov = QEMU_IOVEC_INIT_BUF(qiov, buf,
> +                                            nb_sectors * BDRV_SECTOR_SIZE);

Okay, so you ARE using both the macro...

> @@ -977,17 +963,12 @@ int bdrv_pwritev(BdrvChild *child, int64_t offset, 
> QEMUIOVector *qiov)
>  
>  int bdrv_pwrite(BdrvChild *child, int64_t offset, const void *buf, int bytes)
>  {
> -    QEMUIOVector qiov;
> -    struct iovec iov = {
> -        .iov_base   = (void *) buf,
> -        .iov_len    = bytes,
> -    };
> +    QEMUIOVector qiov = QEMU_IOVEC_INIT_BUF(qiov, NULL, bytes);

Ouch - why are you passing NULL instead of buf?  But this answers why
the macro had to cast - it is indeed casting away const.

> @@ -1229,9 +1209,7 @@ static int coroutine_fn 
> bdrv_co_do_copy_on_readv(BdrvChild *child,
>  
>          if (ret <= 0) {
>              /* Must copy-on-read; use the bounce buffer */
> -            iov.iov_base = bounce_buffer;
> -            iov.iov_len = pnum = MIN(pnum, MAX_BOUNCE_BUFFER);
> -            qemu_iovec_init_external(&local_qiov, &iov, 1);
> +            qemu_iovec_init_buf(&local_qiov, bounce_buffer, pnum);

...and the function.

Ouch - why did you lose the assignment of pnum = MIN() here?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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