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From:   Daniel Colascione <dancol@google.com>
Date:   Mon, 19 Nov 2018 11:39:53 -0800
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Subject: Re: [PATCH v1 2/2] signal: add procfd_signal() syscall
To:     Christian Brauner <christian@brauner.io>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        "Serge E. Hallyn" <serge@hallyn.com>, Jann Horn <jannh@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Aleksa Sarai <cyphar@cyphar.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Tim Murray <timmurray@google.com>,
        linux-man <linux-man@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>
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Yep. That's also what I was talking about, FWIW.

On Mon, Nov 19, 2018 at 11:31 AM, Christian Brauner
<christian@brauner.io> wrote:
> On Mon, Nov 19, 2018 at 01:02:06PM -0600, Eric W. Biederman wrote:
>> Christian Brauner <christian@brauner.io> writes:
>>
>> > On Mon, Nov 19, 2018 at 07:59:24AM -0800, Daniel Colascione wrote:
>> >> You never addressed my comment on the previous patch about your use of
>> >
>> > Sorry, that thread exploded so quickly that I might have missed it.
>> >
>> >> private_data here. Why can't you use the struct pid reference that's
>> >> already in the inode?
>> >
>> > If that's what people prefer we can probably use that. There was
>> > precedent for stashing away such data in fs/proc/base.c already for
>> > various other things including user namespaces and struct mm so I
>> > followed this model. A prior version of my patch (I didn't send out) did
>> > retrive the inode via proc_pid() in .open() took an additional reference
>> > via get_pid() and dropped it in .release(). Do we prefer that?
>>
>> If you are using proc/<pid>/ directories as your file descriptors, you
>> don't need to add an open or a release method at all.  The existing file
>> descriptors hold a reference to the inode which holds a reference the
>> the struct pid.
>>
>> The only time you need to get a reference is when you need a task
>> and kill_pid_info already performs that work for you.
>
> Oh, I see what you and Andy are saying now. Sweet, that means we can
> trim down the patch even more. Less code, less headache.
>
> Thanks!
>
>>
>> So using proc_pid is all you need to do to get the pid from the existing
>> file descriptors.
>>
>> Eric
>>