Re: [Qemu-devel] [RFC PATCH v5 4/6] module: implement module loading function

[Richard Henderson <rth@twiddle.net>]

On 09/11/2013 07:10 AM, Alex Bligh wrote:
> 
> 
> --On 11 September 2013 13:38:27 +0800 Fam Zheng <famz@redhat.com> wrote:
> 
>> +    switch (type) {
>> +    case MODULE_LOAD_BLOCK:
>> +        path = CONFIG_PREFIX "/qemu/block/";
>> +        break;
>> +    case MODULE_LOAD_UI:
>> +        path = CONFIG_PREFIX "/qemu/ui/";
>> +        break;
>> +    case MODULE_LOAD_NET:
>> +        path = CONFIG_PREFIX "/qemu/net/";
>> +        break;
>> +    default:
>> +        return;
>> +    }
>> +
> 
> I appreciate I am coming in late into this discussion, and am only scanning
> the code quickly, so apologies if I have the wrong end of the stick.
> 
> This APPEARS to load modules from
> a) a fixed path determined at compile time
> b) a path which is not dependent on qemu version
> 
> This would make it hard to have 2 versions of qemu installed on a
> system at once, or even develop one version of qemu with another
> version installed. I suspect this will be hard not only for developers,
> but also for distributions, particularly if the idea is to keep vms
> running during upgrades. Consider the case where packages A and B
> both depend on qemu module package C, then you wish to upgrade to
> A', B' and C'. At some point you are likely to want both C and C'
> installed. Is the idea here that QEMU is always built with CONFIG_PREFIX
> having versioning inside it (in a distro environment)?
> 
> Can I suggest that at the very least, it should be possible to specify
> an alternate path to the module directory via the CLI?
> 

If we want dependencies between modules, we may well need to get the
dynamic linker involved with the search directory.  This would rule
out any command-line, or monitor-line altering of the path.

But it does suggest the default being DT_RUNPATH, overridable "near"
the command-line via LD_RUN_PATH.

I also wonder about the utility of the subdirectories above, as
opposed to filename prefixes.


r~