Re: [Qemu-devel] [PATCH 0/3] blockdev: Add read-only option to change-blockdev

[Markus Armbruster]

Max Reitz <address@hidden> writes:

> On 2014-11-28 at 16:43, Markus Armbruster wrote:
>> Kevin Wolf <address@hidden> writes:
>>
>>> Am 20.11.2014 um 13:44 hat Max Reitz geschrieben:
>>>> The 'change' QMP and HMP command allows replacing the medium in drives
>>>> which support this, e.g. floppy disk drives. For some drives, the medium
>>>> carries information about whether it can be written to or not (again,
>>>> floppy drives). Therefore, it should be possible to change the read-only
>>>> state of block devices when changing the loaded medium.
>>>>
>>>> This series adds an optional additional parameter to the 'change' QMP
>>>> and HMP command which allows changing the read-only state in four ways:
>>>>
>>>> - 'retain': Just keep the status as it was before; this is the current
>>>>    behavior and thus this will be the default.
>>>> - 'ro': Force read-only access
>>>> - 'rw': Force writable access
>>>> - 'auto': This opens the new file R/W first, if that fails, the file is
>>>>    opened read-only.
>>> Not sure if 'auto' is worth implementing (it's a typical HMP default
>>> action that no QMP client would use, except that it isn't even the
>>> default for HMP), but the implementation looks correct at least.
>> QMP eschews magic.  I'd prefer to keep 'auto' out.
>>
>> HMP can offer it regardless, if it's useful.  But I doubt it will be.
>> Few users will need to control this, and fewer will realize they can by
>> giving an extra argument.
>
> Well, Kevin made the good point of the user generally knowing whether
> a file should be written to or not. Furthermore, I don't think it
> would be too hard to use rw, then see that access was denied, and then
> use ro, manually. Maybe that's even better than auto, somehow.

Please give it a try.