linux-kernel - Re: [PATCH 1/8] fork: add helper to clone a process

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Date:   Fri, 17 Sep 2021 07:00:35 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Mike Christie <michael.christie@...cle.com>
Cc:     stefanha@...hat.com, jasowang@...hat.com, mst@...hat.com,
        sgarzare@...hat.com, virtualization@...ts.linux-foundation.org,
        christian.brauner@...ntu.com, axboe@...nel.dk,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/8] fork: add helper to clone a process

On Thu, Sep 16, 2021 at 04:20:44PM -0500, Mike Christie wrote:
> The vhost layer has similar requirements as io_uring where its worker
> threads need to access the userspace thread's memory, want to inherit the
> parents's cgroups and namespaces, and be checked against the parent's
> RLIMITs. Right now, the vhost layer uses the kthread API which has
> kthread_use_mm for mem access, and those threads can use
> cgroup_attach_task_all for v1 cgroups, but there are no helpers for the
> other items.
> 
> This adds a helper to clone a process so we can inherit everything we
> want in one call. It's a more generic version of create_io_thread which
> will be used by the vhost layer and io_uring in later patches in this set.
> 
> This patch also exports __set_task_comm and wake_up_new_task which is
> needed by modules to use the new helper. io_uring calls these functions
> already but its always built into the kernel so was not needed before.

Can you build proper APIs please?  e.g. the set_task_comm users
generally want a printf-like varargs caling conventions.  I'd also
much prefer to hide as much as possible in the actual helper.  That is
build a helper that gets the name, a flag to ignore the singals etc
instead of exporting all these random low-level helpers.