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Re: [Qemu-block] [PATCH v2 4/8] qcow: Switch qcow_co_writev to byte-base
From: |
Jeff Cody |
Subject: |
Re: [Qemu-block] [PATCH v2 4/8] qcow: Switch qcow_co_writev to byte-based calls |
Date: |
Mon, 4 Jun 2018 17:27:30 -0400 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Thu, May 31, 2018 at 03:50:42PM -0500, Eric Blake wrote:
> We are gradually moving away from sector-based interfaces, towards
> byte-based. Make the change for the internals of the qcow
> driver write function, by iterating over offset/bytes instead of
> sector_num/nb_sectors, and with a rename of index_in_cluster and
> repurposing of n to track bytes instead of sectors.
>
> A later patch will then switch the qcow driver as a whole over
> to byte-based operation.
>
> Signed-off-by: Eric Blake <address@hidden>
>
> ---
> v2: prefer 64-bit * over 23-bit <<, rename variable for legibility [Kevin]
> ---
> block/qcow.c | 36 +++++++++++++++++-------------------
> 1 file changed, 17 insertions(+), 19 deletions(-)
>
> diff --git a/block/qcow.c b/block/qcow.c
> index b90915218ff..44adeba276c 100644
> --- a/block/qcow.c
> +++ b/block/qcow.c
> @@ -723,13 +723,15 @@ static coroutine_fn int qcow_co_writev(BlockDriverState
> *bs, int64_t sector_num,
> int flags)
> {
> BDRVQcowState *s = bs->opaque;
> - int index_in_cluster;
> + int offset_in_cluster;
> uint64_t cluster_offset;
> int ret = 0, n;
> struct iovec hd_iov;
> QEMUIOVector hd_qiov;
> uint8_t *buf;
> void *orig_buf;
> + int64_t offset = sector_num * BDRV_SECTOR_SIZE;
> + int64_t bytes = nb_sectors * BDRV_SECTOR_SIZE;
>
> assert(!flags);
> s->cluster_cache_offset = -1; /* disable compressed cache */
> @@ -749,16 +751,14 @@ static coroutine_fn int qcow_co_writev(BlockDriverState
> *bs, int64_t sector_num,
>
> qemu_co_mutex_lock(&s->lock);
>
> - while (nb_sectors != 0) {
> -
> - index_in_cluster = sector_num & (s->cluster_sectors - 1);
> - n = s->cluster_sectors - index_in_cluster;
> - if (n > nb_sectors) {
> - n = nb_sectors;
> + while (bytes != 0) {
> + offset_in_cluster = offset & (s->cluster_size - 1);
> + n = s->cluster_size - offset_in_cluster;
> + if (n > bytes) {
> + n = bytes;
> }
> - ret = get_cluster_offset(bs, sector_num << 9, 1, 0,
> - index_in_cluster << 9,
> - (index_in_cluster + n) << 9,
> &cluster_offset);
> + ret = get_cluster_offset(bs, offset, 1, 0, offset_in_cluster,
> + offset_in_cluster + n, &cluster_offset);
> if (ret < 0) {
> break;
> }
> @@ -768,30 +768,28 @@ static coroutine_fn int qcow_co_writev(BlockDriverState
> *bs, int64_t sector_num,
> }
> if (bs->encrypted) {
> assert(s->crypto);
> - if (qcrypto_block_encrypt(s->crypto, sector_num *
> BDRV_SECTOR_SIZE,
> - buf, n * BDRV_SECTOR_SIZE, NULL) < 0) {
> + if (qcrypto_block_encrypt(s->crypto, offset, buf, n, NULL) < 0) {
> ret = -EIO;
> break;
> }
> }
>
> hd_iov.iov_base = (void *)buf;
> - hd_iov.iov_len = n * 512;
> + hd_iov.iov_len = n;
> qemu_iovec_init_external(&hd_qiov, &hd_iov, 1);
> qemu_co_mutex_unlock(&s->lock);
> BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);
> - ret = bdrv_co_writev(bs->file,
> - (cluster_offset >> 9) + index_in_cluster,
> - n, &hd_qiov);
> + ret = bdrv_co_pwritev(bs->file, cluster_offset + offset_in_cluster,
> + n, &hd_qiov, 0);
> qemu_co_mutex_lock(&s->lock);
> if (ret < 0) {
> break;
> }
> ret = 0;
>
> - nb_sectors -= n;
> - sector_num += n;
> - buf += n * 512;
> + bytes -= n;
> + offset += n;
> + buf += n;
> }
> qemu_co_mutex_unlock(&s->lock);
>
> --
> 2.14.3
>
>
Reviewed-by: Jeff Cody <address@hidden>
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