[Devel] [PATCH vz9] dm-qcow2: support mixed compression images

[Pavel Tikhomirov]

On 2/17/25 14:50, Alexander Atanasov wrote:
> Currently code uses only top qcow2 delta to handle decompression.
> Images have compression type in the qcow2 header already set when  loaded.
> To support mixed compression switch to use qio->qcow2 and respective
> qcow2 header so the decompression is performed with the correct type.
> Remove qcow2 argument in functions called from decompression where
> possible and use qio->qcow2 which is the respective qcow2 image for
> the qio, a qio references only one image.
> 
> https://virtuozzo.atlassian.net/browse/VSTOR-97155
> Signed-off-by: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
> ---
>   drivers/md/dm-qcow2-map.c | 74 ++++++++++++++++++++++++---------------
>   1 file changed, 46 insertions(+), 28 deletions(-)
> 
> 
> diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c
> index ccc8d4484049..969f591eb0a1 100644
> --- a/drivers/md/dm-qcow2-map.c
> +++ b/drivers/md/dm-qcow2-map.c
> @@ -3009,8 +3009,9 @@ static int copy_buf_to_bvec_iter(const struct bio_vec *bvec,
>   	return ret;
>   }
>   
> -static int copy_clu_part_to_qio(struct qcow2 *qcow2, const void *buf, struct qio *qio)
> +static int copy_clu_part_to_qio(const void *buf, struct qio *qio)
>   {
> +	struct qcow2 *qcow2 = qio->qcow2;
>   	u32 max, seek, clu_size = qcow2->clu_size;
>   
>   	seek = bytes_off_in_cluster(qcow2, qio);
> @@ -3047,7 +3048,7 @@ static int copy_zcow_slice(loff_t start, loff_t end, void *qio_p,
>   	return copy_buf_to_bvec_iter(bvec, &iter, buf + off, clu_size - off);
>   }
>   
> -static int prepare_zcow_slices(struct qcow2 *qcow2, void *buf, struct qio *qio)
> +static int prepare_zcow_slices(void *buf, struct qio *qio)
>   {
>   	loff_t consumed = 0;
>   	/* Place required slices in that pages like further COW expects */
> @@ -3655,46 +3656,63 @@ static int complete_metadata_writeback(struct qcow2 *qcow2)
>   }
>   
>   /* Process completed compressed READs */
> -static void process_compressed_read(struct qcow2 *qcow2, struct list_head *read_list,
> +static void process_compressed_read(struct list_head *read_list,
>   				    struct list_head *cow_list)
>   {
> +	struct qcow2 *qcow2, *qcow2_prev = NULL;
>   	struct qcow2_bvec *qvec;
>   	struct qio_ext *ext;
>   	int ret;
>   	void *buf = NULL, *arg;
>   	struct qio *qio;
>   	bool for_cow;
> +	size_t dctxlen_alloced = 0;
>   	size_t dctxlen;
>   
>   	if (list_empty(read_list))
>   		return;
>   
> -	if (qcow2->hdr.compression_type == QCOW2_COMPRESSION_TYPE_ZSTD)
> -		dctxlen = zstd_dstream_workspace_bound(qcow2->clu_size);
> -	else
> -		dctxlen = zlib_inflate_workspacesize();
> -
> -
> -	buf = kvmalloc(qcow2->clu_size + dctxlen, GFP_NOIO);
> -	if (!buf) {
> -		end_qios(read_list, BLK_STS_RESOURCE);
> -		return;
> -	}
> -
> -	if (qcow2->hdr.compression_type == QCOW2_COMPRESSION_TYPE_ZSTD) {
> -		arg = zstd_init_dstream(qcow2->clu_size, buf + qcow2->clu_size, dctxlen);
> -		if (!arg) {
> -			end_qios(read_list, BLK_STS_RESOURCE);
> -			kvfree(buf);
> -			return;
> -		}
> -	} else {
> -		arg = buf + qcow2->clu_size;
> -	}
>   
>   	while ((qio = qio_list_pop(read_list)) != NULL) {
>   		qvec = qio->data;
>   		ext = qio->ext;
> +		qcow2 = qio->qcow2;
> +
> +		if (!qcow2_prev || qcow2_prev != qcow2) {
> +			if (qcow2->hdr.compression_type == QCOW2_COMPRESSION_TYPE_ZSTD)
> +				dctxlen = zstd_dstream_workspace_bound(qcow2->clu_size);
> +			else
> +				dctxlen = zlib_inflate_workspacesize();
> +
> +			if (dctxlen_alloced < dctxlen) {
> +				if (buf)
> +					kfree(buf);
> +				buf = kvmalloc(qcow2->clu_size + dctxlen, GFP_NOIO);
> +				if (!buf) {
> +					QC_ERR(qcow2->tgt->ti, "can not allocate decompression buffer:%d",
> +						   qcow2->clu_size + dctxlen);
> +					end_qios(read_list, BLK_STS_RESOURCE);
> +					return;
> +				}
> +				dctxlen_alloced = dctxlen;
> +			}
> +
> +			if (qcow2->hdr.compression_type == QCOW2_COMPRESSION_TYPE_ZSTD) {
> +				arg = zstd_init_dstream(qcow2->clu_size, buf + qcow2->clu_size, dctxlen);
> +				if (!arg) {
> +					end_qios(read_list, BLK_STS_RESOURCE);
> +					kvfree(buf);
> +					return;
> +				}
> +			} else {
> +				arg = buf + qcow2->clu_size;
> +			}
> +		} else {
> +			if (qcow2->hdr.compression_type == QCOW2_COMPRESSION_TYPE_ZSTD) {
> +				zstd_reset_dstream(arg);

This looks like a separate fix of doing reset before qio processing. 
Please, add explanation why we add reset and if having no reset 
previously was an issue.

> +			}
> +		}
> +		qcow2_prev = qcow2;
>   
>   		ret = extract_one_compressed(qcow2, buf, qvec,
>   				    ext->zdata_off, qio->ret, arg);
> @@ -3703,9 +3721,9 @@ static void process_compressed_read(struct qcow2 *qcow2, struct list_head *read_
>   
>   		for_cow = op_is_write(qio->bi_op);
>   		if (!for_cow)
> -			ret = copy_clu_part_to_qio(qcow2, buf, qio);
> +			ret = copy_clu_part_to_qio(buf, qio);
>   		else
> -			ret = prepare_zcow_slices(qcow2, buf, qio);
> +			ret = prepare_zcow_slices(buf, qio);
>   
>   		if (!for_cow || ret) {
>   err:
> @@ -4099,7 +4117,7 @@ void do_qcow2_work(struct work_struct *ws)
>   
>   	process_embedded_qios(qcow2, &embedded_qios, &deferred_qios);
>   	process_deferred_qios(qcow2, &deferred_qios);
> -	process_compressed_read(qcow2, &zread_qios, &cow_data_qios);
> +	process_compressed_read(&zread_qios, &cow_data_qios);
>   	process_backward_merge_write(qcow2, &bwrite_qios);
>   	process_cow_data_write(qcow2, &cow_data_qios);
>   	process_cow_indexes_write(qcow2, &cow_indexes_qios);

-- 
Best regards, Tikhomirov Pavel
Senior Software Developer, Virtuozzo.