Re: [RFC] Unify KVM kernel-space and user-space code into a single project

Antoine Martin
2010-04-08T14:29:17Z

Avi Kivity wrote:
> On 03/24/2010 06:40 PM, Joerg Roedel wrote:
>>
>>> Looks trivial to find a guest, less so with enumerating (still doable).
>>>
>> Not so trival and even more likely to break. Even it perf has the pid of
>> the process and wants to find the directory it has to do:
>>
>> 1. Get the uid of the process
>> 2. Find the username for the uid
>> 3. Use the username to find the home-directory
>>
>> Steps 2. and 3. need nsswitch and/or pam access to get this information
>> from whatever source the admin has configured. And depending on what the
>> source is it may be temporarily unavailable causing nasty timeouts. In
>> short, there are many weak parts in that chain making it more likely to
>> break.
>>
>
> It's true. If the kernel provides something, there are fewer things
> that can break. But if your system is so broken that you can't resolve
> uids, fix that before running perf. Must we design perf for that case?
uid to username can fail when using chroots, or worse point to an
incorrect location (and yes, I do use this)

Sorry if this has been covered / discussion has moved on. Just catching
up with the 500+ messages in my inbox..

Antoine

>
> After all, 'ls -l' will break under the same circumstances. It's hard
> to imagine doing useful work when that doesn't work.
>
>> A kernel-based approach with /proc/<pid>/kvm does not have those issues
>> (and to repeat myself, it is independent from the userspace being used).
>>
>
> It has other issues, which are IMO more problematic.
>