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Re: [Qemu-block] [PATCH v2 04/21] block: Allow references for backing fi
From: |
Max Reitz |
Subject: |
Re: [Qemu-block] [PATCH v2 04/21] block: Allow references for backing files |
Date: |
Fri, 27 Nov 2015 18:28:14 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0 |
On 23.11.2015 16:59, Kevin Wolf wrote:
> For bs->file, using references to existing BDSes has been possible for a
> while already. This patch enables the same for bs->backing_hd.
It's just "backing" now (instead of "backing_hd").
>
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
> block.c | 47 +++++++++++++++++++++++++++++------------------
> block/mirror.c | 2 +-
> include/block/block.h | 3 ++-
> 3 files changed, 32 insertions(+), 20 deletions(-)
An additional thing I believe this patch can do (or a follow-up) is to
remove the part of bdrv_open_inherit() which sets BDRV_O_NO_BACKING if
the @backing option is the empty string.
With the changes done to bdrv_open_backing_file() here, we can easily
put that case into that function (where I think it belongs). If
!reference[0], we can just return success without having actually opened
a backing file.
We may have to think about the case of
{'backing': '', 'backing.driver': 'null-co'}, though. Right now, that is
an error (with a rather obscure error message, probably), and if we want
to keep it an error, we'd have to check whether options is empty in
bdrv_open_backing_file() if !reference[0], and emit a nice error if it
is not ("cannot specify backing options for suppressed backing file" or
something like that).
> diff --git a/block.c b/block.c
> index 675e5a8..ca6c4e9 100644
> --- a/block.c
> +++ b/block.c
> @@ -1182,30 +1182,43 @@ out:
> /*
> * Opens the backing file for a BlockDriverState if not yet open
> *
> - * options is a QDict of options to pass to the block drivers, or NULL for an
> - * empty set of options. The reference to the QDict is transferred to this
> - * function (even on failure), so if the caller intends to reuse the
> dictionary,
> - * it needs to use QINCREF() before calling bdrv_file_open.
> + * bdref_key specifies the key for the image's BlockdevRef in the options
> QDict.
> + * That QDict has to be flattened; therefore, if the BlockdevRef is a QDict
> + * itself, all options starting with "${bdref_key}." are considered part of
> the
> + * BlockdevRef.
> + *
> + * TODO Can this be unified with bdrv_open_image()?
> */
> -int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error
> **errp)
> +int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
> + const char *bdref_key, Error **errp)
> {
> char *backing_filename = g_malloc0(PATH_MAX);
> + char *bdref_key_dot;
> + const char *reference = NULL;
> int ret = 0;
> BlockDriverState *backing_hd;
> + QDict *options;
> + QDict *tmp_parent_options = NULL;
> Error *local_err = NULL;
>
> if (bs->backing != NULL) {
> - QDECREF(options);
> goto free_exit;
> }
>
> /* NULL means an empty set of options */
> - if (options == NULL) {
> - options = qdict_new();
> + if (parent_options == NULL) {
> + tmp_parent_options = qdict_new();
> + parent_options = tmp_parent_options;
> }
>
> bs->open_flags &= ~BDRV_O_NO_BACKING;
> - if (qdict_haskey(options, "file.filename")) {
> +
> + bdref_key_dot = g_strdup_printf("%s.", bdref_key);
> + qdict_extract_subqdict(parent_options, &options, bdref_key_dot);
> + g_free(bdref_key_dot);
> +
> + reference = qdict_get_try_str(parent_options, bdref_key);
> + if (reference || qdict_haskey(options, "file.filename")) {
> backing_filename[0] = '\0';
> } else if (bs->backing_file[0] == '\0' && qdict_size(options) == 0) {
> QDECREF(options);
> @@ -1228,19 +1241,17 @@ int bdrv_open_backing_file(BlockDriverState *bs,
> QDict *options, Error **errp)
> goto free_exit;
> }
>
> - backing_hd = bdrv_new();
> -
> if (bs->backing_format[0] != '\0' && !qdict_haskey(options, "driver")) {
> qdict_put(options, "driver", qstring_from_str(bs->backing_format));
> }
>
> assert(bs->backing == NULL);
This assert() can be dropped along with the bdrv_new() call (they are
related: originally, the bdrv_open_inherit() call below took
&bs->backing_hd as its first parameter, and when that was changed, this
assert() was apparently overlooked).
(http://lists.nongnu.org/archive/html/qemu-block/2015-11/msg00344.html)
Anyway, with the commit message fixed:
Reviewed-by: Max Reitz <address@hidden>
> + backing_hd = NULL;
> ret = bdrv_open_inherit(&backing_hd,
> *backing_filename ? backing_filename : NULL,
> - NULL, options, 0, bs, &child_backing,
> &local_err);
> + reference, options, 0, bs, &child_backing,
> + &local_err);
> if (ret < 0) {
> - bdrv_unref(backing_hd);
> - backing_hd = NULL;
> bs->open_flags |= BDRV_O_NO_BACKING;
> error_setg(errp, "Could not open backing file: %s",
> error_get_pretty(local_err));
> @@ -1253,8 +1264,11 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict
> *options, Error **errp)
> bdrv_set_backing_hd(bs, backing_hd);
> bdrv_unref(backing_hd);
>
> + qdict_del(parent_options, bdref_key);
> +
> free_exit:
> g_free(backing_filename);
> + QDECREF(tmp_parent_options);
> return ret;
> }
>
> @@ -1537,10 +1551,7 @@ static int bdrv_open_inherit(BlockDriverState **pbs,
> const char *filename,
>
> /* If there is a backing file, use it */
> if ((flags & BDRV_O_NO_BACKING) == 0) {
> - QDict *backing_options;
> -
> - qdict_extract_subqdict(options, &backing_options, "backing.");
> - ret = bdrv_open_backing_file(bs, backing_options, &local_err);
> + ret = bdrv_open_backing_file(bs, options, "backing", &local_err);
> if (ret < 0) {
> goto close_and_fail;
> }
> diff --git a/block/mirror.c b/block/mirror.c
> index 0620068..223b7aa 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -648,7 +648,7 @@ static void mirror_complete(BlockJob *job, Error **errp)
> Error *local_err = NULL;
> int ret;
>
> - ret = bdrv_open_backing_file(s->target, NULL, &local_err);
> + ret = bdrv_open_backing_file(s->target, NULL, "backing", &local_err);
> if (ret < 0) {
> error_propagate(errp, local_err);
> return;
> diff --git a/include/block/block.h b/include/block/block.h
> index 73edb1a..6d8ce86 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -210,7 +210,8 @@ BdrvChild *bdrv_open_child(const char *filename,
> const BdrvChildRole *child_role,
> bool allow_none, Error **errp);
> void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd);
> -int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error
> **errp);
> +int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
> + const char *bdref_key, Error **errp);
> int bdrv_append_temp_snapshot(BlockDriverState *bs, int flags, Error **errp);
> int bdrv_open(BlockDriverState **pbs, const char *filename,
> const char *reference, QDict *options, int flags, Error
> **errp);
>
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- [Qemu-block] [PATCH v2 07/21] block: Pass driver-specific options to .bdrv_refresh_filename(), (continued)
- [Qemu-block] [PATCH v2 07/21] block: Pass driver-specific options to .bdrv_refresh_filename(), Kevin Wolf, 2015/11/23
- [Qemu-block] [PATCH v2 09/21] block: Allow specifying child options in reopen, Kevin Wolf, 2015/11/23
- [Qemu-block] [PATCH v2 10/21] block: reopen: Document option precedence and refactor accordingly, Kevin Wolf, 2015/11/23
- [Qemu-block] [PATCH v2 12/21] block: Split out parse_json_protocol(), Kevin Wolf, 2015/11/23
- [Qemu-block] [PATCH v2 08/21] block: Keep "driver" in bs->options, Kevin Wolf, 2015/11/23
- [Qemu-block] [PATCH v2 14/21] blockdev: Set 'format' indicates non-empty drive, Kevin Wolf, 2015/11/23
- [Qemu-block] [PATCH v2 04/21] block: Allow references for backing files, Kevin Wolf, 2015/11/23
- Re: [Qemu-block] [PATCH v2 04/21] block: Allow references for backing files,
Max Reitz <=
- [Qemu-block] [PATCH v2 13/21] block: Introduce bs->explicit_options, Kevin Wolf, 2015/11/23
- [Qemu-block] [PATCH v2 16/21] block: reopen: Extract QemuOpts for generic block layer options, Kevin Wolf, 2015/11/23
- [Qemu-block] [PATCH v2 15/21] qemu-iotests: Remove cache mode test without medium, Kevin Wolf, 2015/11/23
- [Qemu-block] [PATCH v2 11/21] block: Add infrastructure for option inheritance, Kevin Wolf, 2015/11/23
- [Qemu-block] [PATCH v2 17/21] block: Move cache options into options QDict, Kevin Wolf, 2015/11/23
- [Qemu-block] [PATCH v2 18/21] blkdebug: Enable reopen, Kevin Wolf, 2015/11/23