Re: Full-time developer available

[Samuel Thibault]

Robert Millan, le Fri 18 Sep 2015 21:14:30 +0200, a écrit :
> El 17/09/15 a les 23:25, Samuel Thibault ha escrit:
> >Robert Millan, le Thu 17 Sep 2015 21:55:32 +0200, a écrit :
> >>As for the rest of PCI devices, AFAICT they're free to be used by whoever
> >>wants them. My understanding is there's no need for an arbiter / multiplexer
> >>as long as all the code playing with PCI devices is well-aware of its 
> >>limits.
> >
> >Yes, for the daily work, the driver can behave well. But to know where
> >the PCI registers are, you need to read that from the config. And that
> >includes unsafe concurrent accesses (i.e. write to a register, read the
> >value). See inside libpciaccess, x86_pci.c which does inl(); outl();
> >inl(); outl();
> 
> Ah, I see what you mean. This seems like a bug in libpciaccess... the routines
> aren't even thread-safe!

Well, yes, but libpciaccess can't really protect its accesses from
access from other tools.  It could still protect itself from itself,
indeed.

> It looks like a generic problem, affecting all uses of libpciaccess (on other
> OS too).

I guess only the Hurd uses the x86 backend.

> This makes me think on MAP_SHARED mmap of some system-wide file e.g.
> /run/io.lock or such, then an "inter-process mutex" on top of that. Does
> this look sane?

That is defined by posix for semaphores, you just need to pass pshared=1
to sem_init.  It isn't supported yet in GNU/hurd.

> Would a giant lock for all I/O serve the needs of all
> inb/outb users?

Err, you'll probably prefer only a lock on the config space ports, but
yes.

> Would it be possible to solve this in a portable way?

It would probably be more portable to rather use a lock on a file in e.g
/run/lock.

Samuel