Re: [Qemu-devel] [PATCH] block/nfs: add knob to set readahead

[Peter Lieven <pl@kamp.de>]

On 23.06.2014 23:05, Eric Blake wrote:
> On 06/23/2014 02:47 PM, Peter Lieven wrote:
>
>>>> +#ifdef LIBNFS_FEATURE_READAHEAD
>>>> +        } else if (!strcmp(qp->p[i].name, "readahead")) {
>>>> +            nfs_set_readahead(client->context, atoi(qp->p[i].value));
>>>> +#endif
>>> I'm not a fan of adding even more special-casing to the file-name URI
>>> without also adding it to the QAPI schema for use in the blockdev-add
>>> command.  Of course, we don't have structured nfs options for
>>> blockdev-add yet, but maybe it's time to start thinking about that
>>> addition before we do this addition.
>> I would like to leave this for a follow-up and I promise to take care of this.
>> If you could give me a pointer of an existing driver that does this as a reference
>> I would be grateful.
> A good example of a recent conversion to structured options would be the
> blkdebug and blkverify backends (look around commit 1bf20b82), or
> proposed addition of new backends (such as archipelego,
> https://lists.gnu.org/archive/html/qemu-devel/2014-06/msg05309.html).
> It may be a bigger task than you anticipate, and certainly won't make
> the 2.1 timeframe, but it's worth doing so if you're up to the task,
> more power to you :)
>
>> For the read ahead parameter its likely not needed as (at least in my use case)
>> the read ahead makes only sense when converting a compressed QCOW2 Template File
>> which lives on an NFS Share to a RAW Device. So I use it with qemu-img.
>> For a Container File that is used as a VM hard drive I would likely not use read ahead
>> as the operating system itself will implement some sort of read ahead already.
> Even if qemu-img is likely to be the only one ever specifying the
> option, it still makes sense to expose it via QMP, as we are gradually
> trying to move qemu-img over to more exclusive use of QMP (or at least
> the underlying functions reached by QMP) rather than ad-hoc code.  For
> example,
> https://lists.gnu.org/archive/html/qemu-devel/2014-06/msg01822.html).
>

Ok, it looks  like a bit of work. I will put it on my list for 2.2.

Thanks for the pointers,
Peter