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From:   Suren Baghdasaryan <surenb@google.com>
Date:   Thu, 28 Jan 2021 23:15:04 -0800
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Subject: Re: [PATCH 1/1] process_madvise.2: Add process_madvise man page
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc:     linux-man <linux-man@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jann Horn <jannh@google.com>,
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        Jeffrey Vander Stoep <jeffv@google.com>,
        Minchan Kim <minchan@kernel.org>,
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On Thu, Jan 28, 2021 at 12:31 PM Michael Kerrisk (man-pages)
<mtk.manpages@gmail.com> wrote:
>
> Hello Suren,
>
> On 1/28/21 7:40 PM, Suren Baghdasaryan wrote:
> > On Thu, Jan 28, 2021 at 4:24 AM Michael Kerrisk (man-pages)
> > <mtk.manpages@gmail.com> wrote:
> >>
> >> Hello Suren,
> >>
> >> Thank you for writing this page! Some comments below.
> >
> > Thanks for the review!
> > Couple questions below and I'll respin the new version once they are clarified.
>
> Okay. See below.
>
> >> On Wed, 20 Jan 2021 at 21:36, Suren Baghdasaryan <surenb@google.com> wrote:
> >>>
>
> [...]
>
> Thanks for all the acks. That let's me know that you saw what I said.
>
> >>> RETURN VALUE
> >>>     On success, process_madvise() returns the number of bytes advised. This
> >>>     return value may be less than the total number of requested bytes, if an
> >>>     error occurred. The caller should check return value to determine whether
> >>>     a partial advice occurred.
> >>
> >> So there are three return values possible,
> >
> > Ok, I think I see your point. How about this instead:
>
> Well, I'm glad you saw it, because I forgot to finish it. But yes,
> you understood what I forgot to say.
>
> > RETURN VALUE
> >      On success, process_madvise() returns the number of bytes advised. This
> >      return value may be less than the total number of requested bytes, if an
> >      error occurred after some iovec elements were already processed. The caller
> >      should check the return value to determine whether a partial
> > advice occurred.
> >
> >     On error, -1 is returned and errno is set appropriately.
>
> We recently standardized some wording here:
> s/appropriately/to indicate the error/.
>
>
> >>> +.PP
> >>> +The pointer
> >>> +.I iovec
> >>> +points to an array of iovec structures, defined in
> >>
> >> "iovec" should be formatted as
> >>
> >> .I iovec
> >
> > I think it is formatted that way above. What am I missing?
>
> But also in "an array of iovec structures"...
>
> > BTW, where should I be using .I vs .IR? I was looking for an answer
> > but could not find it.
>
> .B / .I == bold/italic this line
> .BR / .IR == alternate bold/italic with normal (Roman) font.
>
> So:
> .I iovec
> .I iovec ,       # so that comma is not italic
> .BR process_madvise ()
> etc.
>
> [...]
>
> >>> +.I iovec
> >>> +if one of its elements points to an invalid memory
> >>> +region in the remote process. No further elements will be
> >>> +processed beyond that point.
> >>> +.PP
> >>> +Permission to provide a hint to external process is governed by a
> >>> +ptrace access mode
> >>> +.B PTRACE_MODE_READ_REALCREDS
> >>> +check; see
> >>> +.BR ptrace (2)
> >>> +and
> >>> +.B CAP_SYS_ADMIN
> >>> +capability that caller should have in order to affect performance
> >>> +of an external process.
> >>
> >> The preceding sentence is garbled. Missing words?
> >
> > Maybe I worded it incorrectly. What I need to say here is that the
> > caller should have both PTRACE_MODE_READ_REALCREDS credentials and
> > CAP_SYS_ADMIN capability. The first part I shamelessly copy/pasted
> > from https://man7.org/linux/man-pages/man2/process_vm_readv.2.html and
> > tried adding the second one to it, obviously unsuccessfully. Any
> > advice on how to fix that?
>
> I think you already got pretty close. How about:
>
> [[
> Permission to provide a hint to another process is governed by a
> ptrace access mode
> .B PTRACE_MODE_READ_REALCREDS
> check (see
> BR ptrace (2));
> in addition, the caller must have the
> .B CAP_SYS_ADMIN
> capability.

In V2 I explanded a bit this part to explain why CAP_SYS_ADMIN is
needed. There were questions about that during my patch review which
adds this requirement
(https://lore.kernel.org/patchwork/patch/1363605), so I thought a
short explanation would be useful.

> ]]
>
> [...]
>
> >>> +.TP
> >>> +.B ESRCH
> >>> +No process with ID
> >>> +.I pidfd
> >>> +exists.
> >>
> >> Should this maybe be:
> >> [[
> >> The target process does not exist (i.e., it has terminated and
> >> been waited on).
> >> ]]
> >>
> >> See pidfd_send_signal(2).
> >
> > I "borrowed" mine from
> > https://man7.org/linux/man-pages/man2/process_vm_readv.2.html but
> > either one sounds good to me. Maybe for pidfd_send_signal the wording
> > about termination is more important. Anyway, it's up to you. Just let
> > me know which one to use.
>
> I think the pidfd_send_signal(2) wording fits better.
>
> [...]
>
> Thanks,
>
> Michael
>
> --
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Linux/UNIX System Programming Training: http://man7.org/training/