Re: [Qemu-devel] [PATCH] linux-user: implement pipe2 syscall

[Martin Mohring]

Riku Voipio wrote:
> On Wed, May 06, 2009 at 12:08:32PM +0100, Jamie Lokier wrote:
>   
>> But it's not a bug to call execve(), or fork() then execve(), in
>> another thread at the same time as descriptors are being created.
>> Those calls scan the whole file descriptor table, and look at the
>> FD_CLOEXEC flags.
>>     
>
> Now this discussion would be much more useful if qemu was actually
> properly threadsafe to begin with...
>
>   
>> I haven't looked too closely at how guest file descriptors are handled
>> in QEMU these days.  In an older version I'm looking at, guest file
>> descriptors are simply host file descriptors so the pipe2 emulation is
>> broken in this way.
>>     
>
>   
>> If QEMU maintained a guest file descriptor table internally, emulating
>> what a kernel does, this would be solved automatically, but it doesn't.
>>     
>
>   
>> You can solve it quite simply for any host kernel with the lock
>> solution I just posted in another mail on this thread.  The same
>> method works for all the other syscalls taking *_CLOEXEC flags, so
>> it's probably a good idea :-)
>>     
>
> Either of these suggested changes are separate new features, and
> would thus need to be implemented as separate patches. Thanks
> for patches in advance :-)
>   
What do we now discuss? A reimplementation of a complete threadsafe user
mode for qemu now? I dont think that this is the scope of the two
patches. What do the architects of user mode say about that? I thought
we have even the problem of a missing qemu user mode Maintainer?