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Re: [Qemu-devel] [PATCH v2 2/5] qcow2: Implement .bdrv_co_preadv()
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH v2 2/5] qcow2: Implement .bdrv_co_preadv() |
Date: |
Mon, 6 Jun 2016 15:32:29 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
On 06/06/2016 08:59 AM, Kevin Wolf wrote:
> Reading from qcow2 images is now byte granularity.
>
> Most of the affected code in qcow2 actually gets simpler with this
> change. The only exception is encryption, which is fixed on 512 bytes
> blocks; in order to keep this working, bs->request_alignment is set for
> encrypted images.
>
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
> block/qcow2-cluster.c | 27 ++++++-------
> block/qcow2.c | 108
> +++++++++++++++++++++++++++-----------------------
> block/qcow2.h | 2 +-
> 3 files changed, 72 insertions(+), 65 deletions(-)
>
> - * on exit, *num is the number of contiguous sectors we can read.
> + * On exit, *bytes is the number of bytes staring at offset that have the
> same
s/staring/starting/
(although "staring" does make for a rather interesting thought :)
> @@ -1389,26 +1402,24 @@ static coroutine_fn int
> qcow2_co_readv(BlockDriverState *bs, int64_t sector_num,
>
> qemu_co_mutex_lock(&s->lock);
>
> - while (remaining_sectors != 0) {
> + while (bytes != 0) {
>
> /* prepare next request */
> - cur_nr_sectors = remaining_sectors;
> + cur_bytes = MIN(bytes, INT_MAX);
> if (s->cipher) {
> - cur_nr_sectors = MIN(cur_nr_sectors,
> - QCOW_MAX_CRYPT_CLUSTERS * s->cluster_sectors);
> + cur_bytes = MIN(cur_bytes,
> + QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size);
> }
Can this ever result in cur_bytes that is not aligned, even though
encryption requires aligned reads? Do you need to round anything to a
sector boundary in this case?
> qemu_co_mutex_unlock(&s->lock);
> - ret = bdrv_co_readv(bs->file->bs,
> - (cluster_offset >> 9) + index_in_cluster,
> - cur_nr_sectors, &hd_qiov);
> + ret = bdrv_co_preadv(bs->file->bs,
> + cluster_offset + offset_in_cluster,
> + cur_bytes, &hd_qiov, 0);
> qemu_co_mutex_lock(&s->lock);
> if (ret < 0) {
> goto fail;
> }
> if (bs->encrypted) {
> assert(s->cipher);
> + assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
> + assert((cur_bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
Hmm, you do check that later on.
So, other than the typo (easy to fix on commit),
Reviewed-by: Eric Blake <address@hidden>
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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