Re: [PATCH RFC 0/9] Launching processes with io_uring

[Pavel Begunkov <asml.silence@gmail.com>]

On 1/18/25 22:33, Askar Safin wrote:
> Pavel Begunkov:
>> At this point it raises a question why it even needs io_uring
>> infra? I don't think it's really helping you. E.g. why not do it
>> as a list of operation in a custom format instead of links? That
>> can be run by a single io_uring request or can even be a normal
>> syscall.
> 
>> Makes me wonder about a different ways of handling. E.g. why should
>> it be run in the created task context (apart from final exec)? Can
>> requests be run as normal by the original task, each will take the
>> half created and not yet launched task as a parameter (in some form),
>> modify it, and the final exec would launch it?
> 
> I totally agree. I think API should look like this:
> 
> ===
> // This may be PID fd or something completely different
> int fd = create_task ();
> 
> task_manipulate (fd, OP_CHDIR, "/");
> task_manipulate (fd, OP_CLOSE, 0);
> task_manipulate (fd, OP_OPEN, "/dev/null", O_RDONLY, 0666);
> 
> task_execve (fd, "/bin/true", argv, envp);
> ===

That's one way of doing it. The api would be nice, it'd fit into
io_uring without extra tricks, and wouldn't even hard io_uring.
Though that could take a good amount of plumbing.

I also wonder, if copying the page table is a performance problem, why
CLONE_VM + exec is not an option? It's flexible, sounds like
posix_spawn does exactly that under the hood, and people tried it
and managed to outperform posix_spawn.

-- 
Pavel Begunkov