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 <mre...@redhat.com>
Reviewed-by: Eric Blake <ebl...@redhat.com>
---
block.c | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 84 insertions(+)
diff --git a/block.c b/block.c
index c33f0e9b42..9179b9b604 100644
--- a/block.c
+++ b/block.c
@@ -998,6 +998,90 @@ static void bdrv_temp_snapshot_options(int *child_flags,
QDict *child_options,
*child_flags &= ~BDRV_O_NATIVE_AIO;
}
+/*
+ * 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 | BDRV_CHILD_METADATA |
+ BDRV_CHILD_FILTERED)) ==
+ BDRV_CHILD_DATA)
+ {
+ 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 always opened read-only */
+ 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);
+ }
+
+ if (parent_is_format && !(role & BDRV_CHILD_COW)) {
+ /*
+ * Our format drivers take care to send flushes and respect
+ * unmap policy, so we can default to enable both on lower
+ * layers regardless of the corresponding parent options.
+ */
+ 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;
+}
+
/*
* Returns the options and flags that bs->file should get if a protocol driver
* is expected, based on the given options and flags for the parent BDS
--
2.24.1
