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Re: [Qemu-devel] [Qemu-block] [PATCH v2 2/8] qcow: Switch get_cluster_of
From: |
Jeff Cody |
Subject: |
Re: [Qemu-devel] [Qemu-block] [PATCH v2 2/8] qcow: Switch get_cluster_offset to be byte-based |
Date: |
Mon, 4 Jun 2018 16:41:09 -0400 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Thu, May 31, 2018 at 03:50:40PM -0500, Eric Blake wrote:
> We are gradually moving away from sector-based interfaces, towards
> byte-based. Make the change for the internal helper function
> get_cluster_offset(), by changing n_start and n_end to by byte
s/by\ byte/be\ byte/
> offsets rather than sector indices within the cluster being
> allocated. However, assert that these values are still
> sector-aligned (at least qcrypto_block_encrypt() still wants that).
> For now we get that alignment for free because we still use
> sector-based driver callbacks.
>
> A later patch will then switch the qcow driver as a whole over
> to byte-based operation; but will still leave things at sector
> alignments as it is not worth auditing the qcow image format
> to worry about sub-sector requests.
>
> Signed-off-by: Eric Blake <address@hidden>
Reviewed-by: Jeff Cody <address@hidden>
>
> ---
> v2: assert sector alignment [Max]
> ---
> block/qcow.c | 29 +++++++++++++++--------------
> 1 file changed, 15 insertions(+), 14 deletions(-)
>
> diff --git a/block/qcow.c b/block/qcow.c
> index 3ba2ca25ea5..42d1bbb7643 100644
> --- a/block/qcow.c
> +++ b/block/qcow.c
> @@ -345,8 +345,8 @@ static int qcow_reopen_prepare(BDRVReopenState *state,
> *
> * 0 to not allocate.
> *
> - * 1 to allocate a normal cluster (for sector indexes 'n_start' to
> - * 'n_end')
> + * 1 to allocate a normal cluster (for sector-aligned byte offsets 'n_start'
> + * to 'n_end' within the cluster)
> *
> * 2 to allocate a compressed cluster of size
> * 'compressed_size'. 'compressed_size' must be > 0 and <
> @@ -440,9 +440,10 @@ static int get_cluster_offset(BlockDriverState *bs,
> if (!allocate)
> return 0;
> BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC);
> + assert(QEMU_IS_ALIGNED(n_start | n_end, BDRV_SECTOR_SIZE));
> /* allocate a new cluster */
> if ((cluster_offset & QCOW_OFLAG_COMPRESSED) &&
> - (n_end - n_start) < s->cluster_sectors) {
> + (n_end - n_start) < s->cluster_size) {
> /* if the cluster is already compressed, we must
> decompress it in the case it is not completely
> overwritten */
> @@ -480,16 +481,15 @@ static int get_cluster_offset(BlockDriverState *bs,
> /* if encrypted, we must initialize the cluster
> content which won't be written */
> if (bs->encrypted &&
> - (n_end - n_start) < s->cluster_sectors) {
> - uint64_t start_sect;
> + (n_end - n_start) < s->cluster_size) {
> + uint64_t start_offset;
> assert(s->crypto);
> - start_sect = (offset & ~(s->cluster_size - 1)) >> 9;
> - for(i = 0; i < s->cluster_sectors; i++) {
> + start_offset = offset & ~(s->cluster_size - 1);
> + for (i = 0; i < s->cluster_size; i += BDRV_SECTOR_SIZE) {
> if (i < n_start || i >= n_end) {
> - memset(s->cluster_data, 0x00, 512);
> + memset(s->cluster_data, 0x00, BDRV_SECTOR_SIZE);
> if (qcrypto_block_encrypt(s->crypto,
> - (start_sect + i) *
> - BDRV_SECTOR_SIZE,
> + start_offset + i,
> s->cluster_data,
> BDRV_SECTOR_SIZE,
> NULL) < 0) {
> @@ -497,8 +497,9 @@ static int get_cluster_offset(BlockDriverState *bs,
> }
> BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);
> ret = bdrv_pwrite(bs->file,
> - cluster_offset + i * 512,
> - s->cluster_data, 512);
> + cluster_offset + i,
> + s->cluster_data,
> + BDRV_SECTOR_SIZE);
> if (ret < 0) {
> return ret;
> }
> @@ -758,8 +759,8 @@ static coroutine_fn int qcow_co_writev(BlockDriverState
> *bs, int64_t sector_num,
> n = nb_sectors;
> }
> ret = get_cluster_offset(bs, sector_num << 9, 1, 0,
> - index_in_cluster,
> - index_in_cluster + n, &cluster_offset);
> + index_in_cluster << 9,
> + (index_in_cluster + n) << 9,
> &cluster_offset);
> if (ret < 0) {
> break;
> }
> --
> 2.14.3
>
>
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