linux-kernel - Re: [PATCH RFC v4 1/1] random: WARN on large getrandom() waits and introduce getrandom2()

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Message-ID: <20190920172609.GA1832@1wt.eu>
Date:   Fri, 20 Sep 2019 19:26:09 +0200
From:   Willy Tarreau <w@....eu>
To:     "Ahmed S. Darwish" <darwish.07@...il.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Lennart Poettering <mzxreary@...inter.de>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        lkml <linux-kernel@...r.kernel.org>, linux-ext4@...r.kernel.org,
        linux-api@...r.kernel.org, linux-man@...r.kernel.org
Subject: Re: [PATCH RFC v4 1/1] random: WARN on large getrandom() waits and
 introduce getrandom2()

Hi Ahmed,

On Fri, Sep 20, 2019 at 03:46:09PM +0200, Ahmed S. Darwish wrote:
> Problem is, glibc is still *really* slow in adopting linux syscall
> wrappers, so I'm not optimistic about that...
>
> I still see the new system call as the sanest path, even provided
> the cost of a new syscall number..

New syscalls are always a pain to deal with in userland, because when
they are introduced, everyone wants them long before they're available
in glibc. So userland has to define NR_xxx for each supported arch and
to perform the call itself.

With flags adoption is instantaneous. Just #ifndef/#define, check if
the flag is supported and that's done. The only valid reason for a new
syscall is when the API changes (e.g. one extra arg, a la accept4()),
which doesn't seem to be the case here. Otherwise please by all means
avoid this in general.

Thanks,
Willy