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block: Add blk_new_open()

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blk_new_with_bs() creates a BlockBackend with an empty BlockDriverState
attached to it. Empty BDSs are not nice, therefore add an alternative
function which combines blk_new_with_bs() with bdrv_open().

Note: In contrast to bdrv_open() which takes a BlockDriver parameter,
blk_new_open() does not take such a parameter. This is because
bdrv_open() opens a BlockDriverState, therefore it is natural to be able
to set the BlockDriver for that BDS. The fact that bdrv_open() can open
more than a single BDS is merely some form of a byproduct.

blk_new_open() on the other hand is intended to be used to create a
whole tree of BlockDriverStates. Therefore, setting a single BlockDriver
does not make much sense. Instead, the drivers to be used for each of
the nodes must be configured through the "options" QDict; including the
driver of the root BDS.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 1423162705-32065-3-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Max Reitz 2015-02-05 13:58:11 -05:00 committed by Stefan Hajnoczi
parent 1ef01253eb
commit ca49a4fdb3
2 changed files with 37 additions and 0 deletions
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34
block/block-backend.c
View file

@ -91,6 +91,40 @@ BlockBackend *blk_new_with_bs(const char *name, Error **errp)
return blk;
}
/*
* Calls blk_new_with_bs() and then calls bdrv_open() on the BlockDriverState.
*
* Just as with bdrv_open(), after having called this function the reference to
* @options belongs to the block layer (even on failure).
*
* TODO: Remove @filename and @flags; it should be possible to specify a whole
* BDS tree just by specifying the @options QDict (or @reference,
* alternatively). At the time of adding this function, this is not possible,
* though, so callers of this function have to be able to specify @filename and
* @flags.
*/
BlockBackend *blk_new_open(const char *name, const char *filename,
const char *reference, QDict *options, int flags,
Error **errp)
{
BlockBackend *blk;
int ret;
blk = blk_new_with_bs(name, errp);
if (!blk) {
QDECREF(options);
return NULL;
}
ret = bdrv_open(&blk->bs, filename, reference, options, flags, NULL, errp);
if (ret < 0) {
blk_unref(blk);
return NULL;
}
return blk;
}
static void blk_delete(BlockBackend *blk)
{
assert(!blk->refcnt);

3
include/sysemu/block-backend.h
View file

@ -62,6 +62,9 @@ typedef struct BlockDevOps {
BlockBackend *blk_new(const char *name, Error **errp);
BlockBackend *blk_new_with_bs(const char *name, Error **errp);
BlockBackend *blk_new_open(const char *name, const char *filename,
const char *reference, QDict *options, int flags,
Error **errp);
void blk_ref(BlockBackend *blk);
void blk_unref(BlockBackend *blk);
const char *blk_name(BlockBackend *blk);