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Re: [Qemu-block] [Qemu-devel] [PATCH 2/8] qcow: Switch get_cluster_offse
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-block] [Qemu-devel] [PATCH 2/8] qcow: Switch get_cluster_offset to be byte-based |
Date: |
Mon, 28 May 2018 12:52:32 +0200 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
Am 25.04.2018 um 20:32 hat Eric Blake geschrieben:
> 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
> offsets rather than sector indices within the cluster being
> allocated.
>
> A later patch will then switch the qcow driver as a whole over
> to byte-based operation.
>
> Signed-off-by: Eric Blake <address@hidden>
> ---
> block/qcow.c | 28 ++++++++++++++--------------
> 1 file changed, 14 insertions(+), 14 deletions(-)
>
> diff --git a/block/qcow.c b/block/qcow.c
> index dd042b8ddbe..32730a8dd91 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 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 <
> @@ -442,7 +442,7 @@ static int get_cluster_offset(BlockDriverState *bs,
> BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC);
> /* 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 +480,15 @@ 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) {
This code is still working in blocks of BDRV_SECTOR_SIZE here - which
you do need to keep at least partially because that's the block size
that qcrypto_block_encrypt() works with. qcrypto_block_qcow_encrypt()
even asserts it.
However, this means that even though n_start and n_end are byte-based
now, the code only works correctly with encrypted images if they are
multiples of BDRV_SECTOR_SIZE. This is currently true and we could
assert it, but it would kind of defeat the purpose of the patch.
I suppose you could make unaligned n_start/n_end work if you round down
n_start and round up n_end to the next sector boundary for the
comparison with i. For unaligned requests, we would then write a bit
more than is actually necessary, but I think that's okay because we're
initialising a previously unallocated cluster, so we don't overwrite
valid data.
Kevin
- Re: [Qemu-block] [Qemu-devel] [PATCH 2/8] qcow: Switch get_cluster_offset to be byte-based,
Kevin Wolf <=