[Libguestfs] [PATCH v4 07/12] v2v: nbdkit: Add the readahead filter unconditionally if it is available.

[Eric Blake]

On 9/21/19 2:59 PM, Richard W.M. Jones wrote:

>> Is it usable without any plugins?  Does the null plugin take much space?  I
>> wouldn't think so.  Would it be too messy to just ship the null plugin
>> unconditionally, even if just for this particular purpose?
> 
> Right!  My original plan was that we could change the API to drop all
> required callbacks.  The "null" plugin would become the plugin which
> had no callbacks and could therefore be built in to the nbdkit binary.
> 
> Unfortunately my plan doesn't quite work because the null plugin has a
> config parameter (nbdkit-zero-plugin is more like this "null" plugin).
> Oh well.

Yeah, the 'zero' plugin is a lot more compact than the 'null' plugin.
Do we have to ship a separate nbdkit-zero.so, or could we make nbdkit
itself behave as if the zero plugin were in use if no actual plugin is
dlloaded?

> 
>> On the other hand any program that relies on such probing to work
>> might depend not only on nbdkit, but also on the null plugin.
> 
> Indeed, or as you say above we could package one of the regular
> plugins with the server to guarantee it is always available.

Even if we require a plugin, always packaging the zero plugin along with
nbdkit seems reasonable (we'd have to tweak the docs a bit to mention
which plugin we settle on as being always available).

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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