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

Zhang, Yanmin
2010-03-25T08:59:44Z

On Wed, 2010-03-24 at 20:20 +0200, Avi Kivity wrote:
> On 03/24/2010 07:47 PM, Arnaldo Carvalho de Melo wrote:
> > Em Wed, Mar 24, 2010 at 06:09:30PM +0200, Avi Kivity escreveu:
> >
> >> Doesn't perf already has a dependency on naming conventions for finding
> >> debug information?
> >>
> > It looks at several places, from most symbol rich (/usr/lib/debug/, aka
> > -debuginfo packages, where we have full symtabs) to poorest (the
> > packaged binary, where we may just have a .dynsym).
> >
> > In an ideal world, it would just get the build-id (a SHA1 cookie that is
> > in an ELF session inserted in every binary (aka DSOs), kernel module,
> > kallsyms or vmlinux file) and use that to look first in a local cache
> > (implemented in perf for a long time already) or in some symbol server.
> >
> > For instance, for a random perf.data file I collected here in my machine
> > I have:
> >
> > [acme@doppio linux-2.6-tip]$ perf buildid-list | grep libpthread
> > 5c68f7afeb33309c78037e374b0deee84dd441f6 /lib64/libpthread-2.10.2.so
> > [acme@doppio linux-2.6-tip]$
> >
> > So I don't have to access /lib64/libpthread-2.10.2.so directly, nor some
> > convention to get a debuginfo in a local file like:
> >
> > /usr/lib/debug/lib64/libpthread-2.10.2.so.debug
> >
> > Instead the tools look at:
> >
> > [acme@doppio linux-2.6-tip]$ l ~/.debug/.build-id/5c/68f7afeb33309c78037e374b0deee84dd441f6
> > lrwxrwxrwx 1 acme acme 73 2010-01-06 18:53 /home/acme/.debug/.build-id/5c/68f7afeb33309c78037e374b0deee84dd441f6 -> ../../lib64/libpthread-2.10.2.so/5c68f7afeb33309c78037e374b0deee84dd441f6*
> >
> > To find the file for that specific build-id, not the one installed in my
> > machine (or on the different machine, of a different architecture) that
> > may be completely unrelated, a new one, or one for a different arch.
> >
>
> Thanks. I believe qemu could easily act as a symbol server for this use
> case.

I spent a couple of days to investigate why sshfs/fuse doesn't work well with
procfs and sysfs. Just after my patch against fuse is ready almost, I found
fuse already supports such access by direct I/O. With parameter -o direct_io,
it could work well.

Here is an example to mount / from a guest os.
#sshfs -p 5551 -o direct_io localhost:/ guestmount

We can read files and write files if permission is ok.

I will go ahead to support multiple guest os instance statistics parsing.

Yanmin