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Re: [Qemu-block] [PATCH v5 14/42] block: Use CAFs when working with back
From: |
Vladimir Sementsov-Ogievskiy |
Subject: |
Re: [Qemu-block] [PATCH v5 14/42] block: Use CAFs when working with backing chains |
Date: |
Fri, 14 Jun 2019 13:26:15 +0000 |
13.06.2019 1:09, Max Reitz wrote:
> Use child access functions when iterating through backing chains so
> filters do not break the chain.
>
> Signed-off-by: Max Reitz <address@hidden>
> ---
> block.c | 40 ++++++++++++++++++++++++++++------------
> 1 file changed, 28 insertions(+), 12 deletions(-)
>
> diff --git a/block.c b/block.c
> index 11f37983d9..505b3e9a01 100644
> --- a/block.c
> +++ b/block.c
> @@ -4261,7 +4261,8 @@ int bdrv_change_backing_file(BlockDriverState *bs,
> }
>
> /*
> - * Finds the image layer in the chain that has 'bs' as its backing file.
> + * Finds the image layer in the chain that has 'bs' (or a filter on
> + * top of it) as its backing file.
> *
> * active is the current topmost image.
> *
> @@ -4273,11 +4274,18 @@ int bdrv_change_backing_file(BlockDriverState *bs,
> BlockDriverState *bdrv_find_overlay(BlockDriverState *active,
> BlockDriverState *bs)
> {
> - while (active && bs != backing_bs(active)) {
> - active = backing_bs(active);
> + bs = bdrv_skip_rw_filters(bs);
> + active = bdrv_skip_rw_filters(active);
> +
> + while (active) {
> + BlockDriverState *next = bdrv_backing_chain_next(active);
> + if (bs == next) {
> + return active;
> + }
> + active = next;
> }
>
> - return active;
> + return NULL;
> }
Semantics changed for this function.
It is used in two places
1. from bdrv_find_base wtih @bs=NULL, it should be unchanged, as I hope we will
never have
filter node as a bottom of some valid chain
2. from qmp_block_commit, only to check op-blocker... hmmm. I really don't
understand,
why do we check BLOCK_OP_TYPE_COMMIT_TARGET on top_bs overlay.. top_bs overlay
is out of the job,
what is this check for?
>
> /* Given a BDS, searches for the base layer. */
> @@ -4421,9 +4429,7 @@ int bdrv_drop_intermediate(BlockDriverState *top,
> BlockDriverState *base,
> * other intermediate nodes have been dropped.
> * If 'top' is an implicit node (e.g. "commit_top") we should skip
> * it because no one inherits from it. We use explicit_top for that. */
> - while (explicit_top && explicit_top->implicit) {
> - explicit_top = backing_bs(explicit_top);
> - }
> + explicit_top = bdrv_skip_implicit_filters(explicit_top);
> update_inherits_from = bdrv_inherits_from_recursive(base, explicit_top);
>
> /* success - we can delete the intermediate states, and link top->base
> */
> @@ -4902,7 +4908,7 @@ BlockDriverState *bdrv_lookup_bs(const char *device,
> bool bdrv_chain_contains(BlockDriverState *top, BlockDriverState *base)
> {
> while (top && top != base) {
> - top = backing_bs(top);
> + top = bdrv_filtered_bs(top);
> }
>
> return top != NULL;
> @@ -5141,7 +5147,17 @@ BlockDriverState
> *bdrv_find_backing_image(BlockDriverState *bs,
>
> is_protocol = path_has_protocol(backing_file);
>
> - for (curr_bs = bs; curr_bs->backing; curr_bs = curr_bs->backing->bs) {
> + /*
> + * Being largely a legacy function, skip any filters here
> + * (because filters do not have normal filenames, so they cannot
> + * match anyway; and allowing json:{} filenames is a bit out of
> + * scope).
> + */
> + for (curr_bs = bdrv_skip_rw_filters(bs);
> + bdrv_filtered_cow_child(curr_bs) != NULL;
> + curr_bs = bdrv_backing_chain_next(curr_bs))
> + {
> + BlockDriverState *bs_below = bdrv_backing_chain_next(curr_bs);
>
> /* If either of the filename paths is actually a protocol, then
> * compare unmodified paths; otherwise make paths relative */
> @@ -5149,7 +5165,7 @@ BlockDriverState
> *bdrv_find_backing_image(BlockDriverState *bs,
> char *backing_file_full_ret;
>
> if (strcmp(backing_file, curr_bs->backing_file) == 0) {
hmm, interesting, what bs->backing_file now means? It's strange enough to store
such field on
bds, when we have backing link anyway..
> - retval = curr_bs->backing->bs;
> + retval = bs_below;
> break;
> }
> /* Also check against the full backing filename for the image */
> @@ -5159,7 +5175,7 @@ BlockDriverState
> *bdrv_find_backing_image(BlockDriverState *bs,
> bool equal = strcmp(backing_file, backing_file_full_ret) ==
> 0;
> g_free(backing_file_full_ret);
> if (equal) {
> - retval = curr_bs->backing->bs;
> + retval = bs_below;
> break;
> }
> }
> @@ -5185,7 +5201,7 @@ BlockDriverState
> *bdrv_find_backing_image(BlockDriverState *bs,
> g_free(filename_tmp);
>
> if (strcmp(backing_file_full, filename_full) == 0) {
> - retval = curr_bs->backing->bs;
> + retval = bs_below;
> break;
> }
> }
>
--
Best regards,
Vladimir
- Re: [Qemu-block] [PATCH v5 11/42] block: Add bdrv_supports_compressed_writes(), (continued)
[Qemu-block] [PATCH v5 15/42] block: Re-evaluate backing file handling in reopen, Max Reitz, 2019/06/12
[Qemu-block] [PATCH v5 16/42] block: Use child access functions when flushing, Max Reitz, 2019/06/12