On 07/13/2017 05:01 AM, Manos Pitsidianakis wrote:
The following functions fail if bs->drv is a filter and does not
implement them:
bdrv_probe_blocksizes
bdrv_probe_geometry
bdrv_truncate
bdrv_has_zero_init
bdrv_get_info
Instead, the call should be passed to bs->file if it exists, to allow
filter drivers to support those methods without implementing them. This
commit makes `drv->is_filter = true` imply that these callbacks will be
forwarded to bs->file by default, so disabling support for these
functions must be done explicitly.
Reviewed-by: Eric Blake <address@hidden>
I would have dropped R-b on the grounds that you added comments to
'is_filter' (good! but non-trivial), to make sure it gets a
grammar/wording review of the new content. Furthermore, your patch had
a semantic change due to the rebase, and looking at that change...
Reviewed-by: Stefan Hajnoczi <address@hidden>
Signed-off-by: Manos Pitsidianakis <address@hidden>
---
@@ -3420,11 +3424,15 @@ int bdrv_truncate(BdrvChild *child, int64_t offset,
PreallocMode prealloc,
assert(child->perm & BLK_PERM_RESIZE);
+ /* if bs->drv == NULL, bs is closed, so there's nothing to do here */
if (!drv) {
error_setg(errp, "No medium inserted");
return -ENOMEDIUM;
}
if (!drv->bdrv_truncate) {
+ if (bs->file && drv->is_filter) {
+ return bdrv_truncate(bs->file, prealloc, offset, errp);
...ouch - you got it wrong. s/prealloc, offset/offset, prealloc/
+++ b/include/block/block_int.h
@@ -87,7 +87,11 @@ struct BlockDriver {
const char *format_name;
int instance_size;
- /* set to true if the BlockDriver is a block filter */
+ /* set to true if the BlockDriver is a block filter. Block filters pass
+ * certain callbacks that refer to data (see block.c) to their bs->file if
+ * the driver doesn't implement them. Drivers that do not wish to forward
+ * must implement them and return -ENOTSUP.
+ */
bool is_filter;
I'm okay with the new comment.
With the swapped parameter order fixed (the maintainer can probably do
that),
Reviewed-by: Eric Blake <address@hidden>
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