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Date:   Tue, 18 Apr 2023 09:54:42 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Alejandro Colomar <alx.manpages@gmail.com>
Cc:     Sergei Zhirikov <sfzhi@yahoo.com>, linux-man@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: Checking for support of ptrace(PTRACE_SEIZE,...) on older kernels
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Hi Alejandro,

On 04/17, Alejandro Colomar wrote:
>
> On 4/17/23 13:50, Oleg Nesterov wrote:
> > Well, from https://man7.org/linux/man-pages/man2/ptrace.2.html
> >
> >        ESRCH  The specified process does not exist, or is not currently
> >               being traced by the caller, or is not stopped (for
> >               requests that require a stopped tracee).
> >
> > so if the kernel doesn't support PTRACE_SEIZE then ptrace(PTRACE_SEIZE)
> > should fail with -ESRCH as documented.
> >
> > Perhaps this part
> >
> >        EIO    request is invalid, or ...
> >
> > can be improvef a bit to explain that this happens if the target is already
> > traced by us and stopped.
>
> I'm not sure if it's necessary.  When several errors happen at the same time,
> there's usually no documentation about which takes precedence, with few
> exceptions.

Yes, agreed.

I just tried to understand where did this ESRCH/EIO confusion come from.

Oleg.