Re: [Qemu-devel] [PATCH v3 08/10] block: Allow changing 'discard' on reopen

[Alberto Garcia]

On Thu 06 Sep 2018 11:37:08 AM CEST, Alberto Garcia <address@hidden> wrote:
> 'discard' is one of the basic BlockdevOptions available for all
> drivers, but it's not handled by bdrv_reopen_prepare() so any attempt
> to change it results in an error:
>
>    (qemu) qemu-io virtio0 "reopen -o discard=on"
>    Cannot change the option 'discard'
>
> Since there's no reason why we shouldn't allow changing it and the
> implementation is simple let's just do it.
>
> Signed-off-by: Alberto Garcia <address@hidden>

A side effect of this change that I hadn't noticed when I sent this
patch: protocol nodes have the "discard" option set to "unmap" by
default (by bdrv_inherited_options()), and that sets the BDRV_O_UNMAP
flag.

However that flag is cleared during reopen even though the "discard"
option remains there. So thanks to this patch the flag correctly
reflects the value of the option after reopen.

Is it worth sending the patch again with an updated commit message that
explains this?

Berto