Re: [Qemu-devel] [PATCH v6 22/42] block: Fix bdrv_get_allocated_file_size's fallback

[Kevin Wolf]

Am 09.08.2019 um 18:13 hat Max Reitz geschrieben:
> If the driver does not implement bdrv_get_allocated_file_size(), we
> should fall back to cumulating the allocated size of all non-COW
> children instead of just bs->file.
> 
> Suggested-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> Signed-off-by: Max Reitz <address@hidden>

This smells like an overgeneralisation, but if we want to count all vmdk
extents, the qcow2 external data file, etc. it's an improvement anyway.
A driver that has a child that should not be counted must just remember
to implement the callback.

Let me think of an example... How about quorum, for a change? :-)
Or the second blkverify child.

Or eventually the block job filter nodes.

Ehm... Maybe I should just take back what I said first. It almost feels
like it would be better if qcow2 and vmdk explicitly used a handler that
counts all children (could still be a generic one in block.c) rather
than having to remember to disable the functionality everywhere where we
don't want to have it.

And please adjust the comment for bdrv_get_allocated_file_size(), it
only talks about a single file as if trees didn't exist. Actually, it
doesn't even seem so easy to define. Maybe primary node + storage nodes?
Then vmdk needs to expose its extents as storage nodes (plural!), but
in the long run that might be needed anyway.

Kevin