[Devel] [PATCH VZ10 v2 02/10] drivers/md/dm-qcow2: generalize COW index update machinery
Vasileios Almpanis
vasileios.almpanis at virtuozzo.com
Wed Aug 19 14:05:02 MSK 2026
> The two-stage L1/L2 entry update pipeline is not COW-specific:
> backward merge already uses it to zero L2 entries, and upcoming
> discard support will be the third user. Rename it to reflect
> what it does.
>
> No functional changes.
>
> Feature: dm-qcow2: block device over QCOW2 files driver
> https://virtuozzo.atlassian.net/browse/VSTOR-139406
> Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
>
> diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c
> index 2cd8e174049f..08d46eb177dd 100644
> --- a/drivers/md/dm-qcow2-map.c
> +++ b/drivers/md/dm-qcow2-map.c
> @@ -2579,10 +2579,10 @@ static int prepare_l1l2_allocation(struct qcow2 *qcow2, struct qio *qio,
> * we have to wait all previous READs. We do that around
> * index wb. See md->wpc_noread_count update details.
> */
> -static int prepare_l_entry_cow(struct qcow2 *qcow2, struct qcow2_map *map,
> - struct qio *qio, struct md_page *md,
> - u32 index_in_page, loff_t cow_clu_pos,
> - loff_t cow_clu_end, u8 cow_level)
> +static int prepare_l_entry_replace(struct qcow2 *qcow2, struct qcow2_map *map,
> + struct qio *qio, struct md_page *md,
> + u32 index_in_page, loff_t unuse_clu_pos,
> + loff_t unuse_clu_end, u8 lx_level)
> {
> struct lock_desc *lockd = NULL;
> struct qio_ext *ext;
> @@ -2591,9 +2591,9 @@ static int prepare_l_entry_cow(struct qcow2 *qcow2, struct qcow2_map *map,
> return -ENOMEM;
>
> ext = qio->ext;
> - ext->cow_clu_pos = cow_clu_pos;
> - ext->cow_clu_end = cow_clu_end;
> - ext->cow_level = cow_level;
> + ext->unuse_clu_pos = unuse_clu_pos;
> + ext->unuse_clu_end = unuse_clu_end;
> + ext->lx_level = lx_level;
>
> spin_lock_irq(&qcow2->md_pages_lock);
> if (!md->lockd) {
> @@ -2614,23 +2614,23 @@ static int prepare_l_entry_cow(struct qcow2 *qcow2, struct qcow2_map *map,
> return 1;
> }
>
> -static int prepare_l1l2_cow(struct qcow2 *qcow2, struct qio *qio,
> - struct qcow2_map *map)
> +static int prepare_l1l2_replace(struct qcow2 *qcow2, struct qio *qio,
> + struct qcow2_map *map)
> {
> if (WARN_ON_ONCE(!(map->level & L1_LEVEL)))
> return -EIO; /* Sanity check: L1 must be cached */
>
> if (!(map->level & L2_LEVEL)) {
> - return prepare_l_entry_cow(qcow2, map, qio, map->l1.md,
> - map->l1.index_in_page,
> - map->cow_clu_pos,
> - map->cow_clu_end, L1_LEVEL);
> + return prepare_l_entry_replace(qcow2, map, qio, map->l1.md,
> + map->l1.index_in_page,
> + map->cow_clu_pos,
> + map->cow_clu_end, L1_LEVEL);
> }
>
> - return prepare_l_entry_cow(qcow2, map, qio, map->l2.md,
> - map->l2.index_in_page,
> - map->cow_clu_pos,
> - map->cow_clu_end, L2_LEVEL);
> + return prepare_l_entry_replace(qcow2, map, qio, map->l2.md,
> + map->l2.index_in_page,
> + map->cow_clu_pos,
> + map->cow_clu_end, L2_LEVEL);
> }
>
> static void backward_merge_write_complete(struct qcow2_target *tgt, struct qio *unused,
> @@ -2648,7 +2648,7 @@ static void backward_merge_write_complete(struct qcow2_target *tgt, struct qio *
> WARN_ON_ONCE(qio->flags & QIO_IS_DISCARD_FL);
> qio->flags |= QIO_IS_DISCARD_FL;
>
> - qio->queue_list_id = QLIST_COW_INDEXES;
> + qio->queue_list_id = QLIST_INDEXES_WRITE;
> qcow2_dispatch_qios(qcow2, qio, NULL);
> }
>
> @@ -2704,7 +2704,7 @@ static int prepare_backward_merge(struct qcow2 *qcow2, struct qio **qio,
> if (!op_is_write((*qio)->bi_op)) {
> /*
> * READ qio may data may be contained in several deltas.
> - * We can't read lower delta after prepare_l1l2_cow()
> + * We can't read lower delta after prepare_l1l2_replace()
> * prepares us.
> */
> aux_qio = qcow2_alloc_qio(qcow2->tgt->qio_pool, true);
> @@ -2725,10 +2725,10 @@ static int prepare_backward_merge(struct qcow2 *qcow2, struct qio **qio,
> }
>
> /*
> - * Mark as COW, as this completely defers any parallel qios.
> - * @qio is COW status holder.
> + * Lock the entry, as this completely defers any parallel qios.
> + * @qio is the lock holder.
> */
> - ret = prepare_l1l2_cow(qcow2, *qio, map);
> + ret = prepare_l1l2_replace(qcow2, *qio, map);
> if (ret < 0) {
> (*qio)->bi_status = errno_to_blk_status(ret);
> goto endio;
> @@ -2736,13 +2736,13 @@ static int prepare_backward_merge(struct qcow2 *qcow2, struct qio **qio,
>
> if (!map->clu_is_cow) {
> /* Forced set these to unuse them after discard */
> - (*qio)->ext->cow_clu_pos = map->data_clu_pos;
> - (*qio)->ext->cow_clu_end = map->data_clu_pos + qcow2->clu_size;
> + (*qio)->ext->unuse_clu_pos = map->data_clu_pos;
> + (*qio)->ext->unuse_clu_end = map->data_clu_pos + qcow2->clu_size;
> }
>
> return 1;
> endio:
> - qio_endio(*qio); /* Breaks COW set in prepare_l1l2_cow() */
> + qio_endio(*qio); /* Releases the lock set in prepare_l1l2_replace() */
> return 0;
> }
>
> @@ -3348,7 +3348,7 @@ static int handle_metadata(struct qcow2 *qcow2, struct qio **qio,
> (!qio_is_fully_alloced(qcow2, *qio, map) || map->clu_is_cow)) {
> if (map->clu_is_cow) {
> /* COW to compressed or shared with snapshot cluster */
> - ret = prepare_l1l2_cow(qcow2, *qio, map);
> + ret = prepare_l1l2_replace(qcow2, *qio, map);
> } else if ((map->level & L2_LEVEL) &&
> qio_border_is_inside_unmapped_unit(qcow2, *qio, map) &&
> maybe_mapped_in_lower_delta(qcow2, *qio)) {
> @@ -3358,7 +3358,7 @@ static int handle_metadata(struct qcow2 *qcow2, struct qio **qio,
> * snapshots). Here is data COW on L2_LEVEL.
> */
> map->backing_file_cow = true;
> - ret = prepare_l1l2_cow(qcow2, *qio, map);
> + ret = prepare_l1l2_replace(qcow2, *qio, map);
> } else if (unlikely(op_is_discard((*qio)->bi_op) &&
> (map->level & L2_LEVEL))) {
> if (!map->data_clu_alloced) {
> @@ -3837,7 +3837,7 @@ static void cow_data_write_endio(struct qcow2_target *tgt, struct qio *unused,
> qio->bi_status = bi_status;
> qio_endio(qio);
> } else {
> - qio->queue_list_id = QLIST_COW_INDEXES;
> + qio->queue_list_id = QLIST_INDEXES_WRITE;
> qcow2_dispatch_qios(qcow2, qio, NULL);
> }
> }
> @@ -3885,7 +3885,7 @@ static void sliced_cow_data_write_complete(struct qcow2_target *tgt, struct qio
> qio->bi_status = bi_status;
> qio_endio(qio);
> } else {
> - qio->queue_list_id = QLIST_COW_INDEXES;
> + qio->queue_list_id = QLIST_INDEXES_WRITE;
> qcow2_dispatch_qios(qcow2, qio, NULL);
> }
> }
> @@ -3919,7 +3919,7 @@ static void process_cow_data_write(struct qcow2 *qcow2, struct list_head *cow_li
> ext = qio->ext;
>
> if (ext->only_set_ext_l2) {
> - WARN_ON_ONCE(ext->cow_level != L2_LEVEL);
> + WARN_ON_ONCE(ext->lx_level != L2_LEVEL);
> pos = ext->allocated_clu_pos;
> goto submit;
> }
> @@ -3938,14 +3938,14 @@ static void process_cow_data_write(struct qcow2 *qcow2, struct list_head *cow_li
> ext->allocated_clu_pos = pos;
> ext->cleanup_mask |= FREE_ALLOCATED_CLU;
> submit:
> - if (ext->cow_level == L2_LEVEL)
> + if (ext->lx_level == L2_LEVEL)
> submit_sliced_cow_data_write(qcow2, qio, pos);
> else
> submit_cow_data_write(qcow2, qio, pos);
> }
> }
>
> -static void process_cow_indexes_write(struct qcow2 *qcow2,
> +static void process_indexes_write(struct qcow2 *qcow2,
> struct list_head *qio_list)
> {
NIT: qvec is unused. Its only set here, so lets just drop it since we touch this
function.
--
Vasileios Almpanis <vasileios.almpanis at virtuozzo.com>
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