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block: Add generic bdrv_inherited_options()

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After the series this patch belongs to, we want to have a common
BdrvChildClass that encompasses all of child_file, child_format, and
child_backing.  Such a single class needs a single .inherit_options()
implementation, and this patch introduces it.

The next patch will show how the existing implementations can fall back
to it just by passing appropriate BdrvChildRole and parent_is_format
values.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200513110544.176672-11-mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Max Reitz 2020-05-13 13:05:20 +02:00 committed by Kevin Wolf
parent b054ff7354
commit fae8bd3904
1 changed files with 81 additions and 0 deletions
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81
block.c
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@ -1356,6 +1356,87 @@ const BdrvChildClass child_backing = {
.set_aio_ctx = bdrv_child_cb_set_aio_ctx,
};
/*
* Returns the options and flags that a generic child of a BDS should
* get, based on the given options and flags for the parent BDS.
*/
static void __attribute__((unused))
bdrv_inherited_options(BdrvChildRole role, bool parent_is_format,
int *child_flags, QDict *child_options,
int parent_flags, QDict *parent_options)
{
int flags = parent_flags;
/*
* First, decide whether to set, clear, or leave BDRV_O_PROTOCOL.
* Generally, the question to answer is: Should this child be
* format-probed by default?
*/
/*
* Pure and non-filtered data children of non-format nodes should
* be probed by default (even when the node itself has BDRV_O_PROTOCOL
* set). This only affects a very limited set of drivers (namely
* quorum and blkverify when this comment was written).
* Force-clear BDRV_O_PROTOCOL then.
*/
if (!parent_is_format &&
(role & BDRV_CHILD_DATA) &&
!(role & (BDRV_CHILD_METADATA | BDRV_CHILD_FILTERED)))
{
flags &= ~BDRV_O_PROTOCOL;
}
/*
* All children of format nodes (except for COW children) and all
* metadata children in general should never be format-probed.
* Force-set BDRV_O_PROTOCOL then.
*/
if ((parent_is_format && !(role & BDRV_CHILD_COW)) ||
(role & BDRV_CHILD_METADATA))
{
flags |= BDRV_O_PROTOCOL;
}
/*
* If the cache mode isn't explicitly set, inherit direct and no-flush from
* the parent.
*/
qdict_copy_default(child_options, parent_options, BDRV_OPT_CACHE_DIRECT);
qdict_copy_default(child_options, parent_options, BDRV_OPT_CACHE_NO_FLUSH);
qdict_copy_default(child_options, parent_options, BDRV_OPT_FORCE_SHARE);
if (role & BDRV_CHILD_COW) {
/* backing files are opened read-only by default */
qdict_set_default_str(child_options, BDRV_OPT_READ_ONLY, "on");
qdict_set_default_str(child_options, BDRV_OPT_AUTO_READ_ONLY, "off");
} else {
/* Inherit the read-only option from the parent if it's not set */
qdict_copy_default(child_options, parent_options, BDRV_OPT_READ_ONLY);
qdict_copy_default(child_options, parent_options,
BDRV_OPT_AUTO_READ_ONLY);
}
/*
* bdrv_co_pdiscard() respects unmap policy for the parent, so we
* can default to enable it on lower layers regardless of the
* parent option.
*/
qdict_set_default_str(child_options, BDRV_OPT_DISCARD, "unmap");
/* Clear flags that only apply to the top layer */
flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING | BDRV_O_COPY_ON_READ);
if (role & BDRV_CHILD_METADATA) {
flags &= ~BDRV_O_NO_IO;
}
if (role & BDRV_CHILD_COW) {
flags &= ~BDRV_O_TEMPORARY;
}
*child_flags = flags;
}
static int bdrv_open_flags(BlockDriverState *bs, int flags)
{
int open_flags = flags;