Re: [AVFS] resurrection of AVFS

[Miklos Szeredi <miklos@sz...>]

> Source code is nearly uncommented :( No tutorial, no API
> documentation, this situation could not attract more developers to
> use this library in their projects. I could write a basic tutorial
> with examples of use with some help from you.  Investigating
> runtest.c is a good start point, are there more examples anywhere
> else?

Libavfs is mainly used by 'avfscoda' and 'preload' neither of which is
a very good example.

> Well, as an API I could count functions from "virtual.h". Correct me
> if I'm wrong.  There is no documentation but functions from
> virtual.h seem s to behave like their libc counterpards. Function
> virt_read() behaves like read() but with support for reading from
> archives, it takes the same arguments, it return the same error
> codes and so on.

Yes, that is how it's supposed to work.

> Can I use AVFS for reading ordinary (real) files from local?
> I hope I can.

Yes though there are problems with this (see discussion with Ralf
Hoffmann).

> How to set temporary directory for archive cache?

/tmp is used, and this can't be changed currently.  There's a patch by
Peter Kundrat that fixes this (attached), but there's a possible
buffer overflow in this, and I haven't yet integrated a fixed version.

> When is cache cleaned? Am I supposed to do it explicitly?
>     fd = virt_open("/#avfsstat/cache/clear", O_WRONLY, 0);
>     res = virt_write(fd, "1", 1);
>     res = virt_close(fd);
> ..striped function flush_cache() in runtest.c

Yes.  This is equivalent to "echo 1 > /#avfsstat/cache/clear"

> How you test archive change the situation someone copy file into the
> ZIP file.  In which sourcefile, which function I can foud it?  Is
> there something like 'dirty flag'?

The file modification time and other parameters are checked.  The
function is arch_same() in archive.c.

> Is some kind of server started to keep tracks of opened archives?
> (suppose using avfs as library, no avfscoda, preload or fuse)

No.  If you want to have persistent cache, then you must create a
server which uses libfuse, and client library which communicates with
the server.  Basically this is what preload does.

> >From sourcecode organisation it looks like AVFS comes in four flavour.
> - library (layer libary above some functions from glibc)
> - avfscoda
> - preload (overload some methods in libc/glibc, so applications use avfs transparetly without)
> - fuse module
> 
> In documentation only flavours 2 and 3 are mentioned!
> 
> >From further investigation of mail-lists - only flavour 1 is fully
> >operational now, flavours 2 - 4 seems not to be fully operational
> >(or not operational at all) in newer glibc and kernels (>2.6.x).

1 (libavfs) is system independent, and hence should work in any UNIX
like environment.

2 (avfscoda) works on 2.4 kernels, and there's an effort by Olivier
Valentin to make it work on 2.6 kernels too.  Attached his patch which
makes avfscoda compile under 2.6.

3 (avfs-preload) worked on older Solaris versions (I don't have a
Solaris machine anymore, so I can't test newer versions).

4 (avfs-fuse) works on 2.4 and 2.6, but is in an experimental state.

Thanks,
Miklos

[AVFS] AVFS with linux kernel 2.6

[Olivier Valentin <olivier.valentin@im...>]

I made a little patch for avfs that deals with the new CodaFID (128bits) 
of kernel 2.6.
Since in the new kernel syscall table shouldn't be touched be modules, I 
don't know how to make the redir module work...

Any idea ?

Olivier