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 <kw...@redhat.com> > --- > 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 <mre...@redhat.com> > + 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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