From: Eric Blake <eblake@redhat.com>
To: Richard Henderson <rth@twiddle.net>,
Peter Maydell <peter.maydell@linaro.org>,
Richard Henderson <richard.henderson@linaro.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] [PATCH] linux-user: Use *at functions to implement interp_prefix
Date: Tue, 13 Feb 2018 10:38:18 -0600 [thread overview]
Message-ID: <aff1a8c0-4e99-b52e-f933-fdc900bd91fd@redhat.com> (raw)
In-Reply-To: <18af5519-95cd-f00e-1915-75183e94eb38@twiddle.net>
On 02/13/2018 09:31 AM, Richard Henderson wrote:
>> I wonder if there are guest programs that make assumptions about
>> file descriptor numbers such that it would be worthwhile dup2'ing
>> the interp_dirfd away from the presumably low number fd it will
>> get by default into something larger...
>
> Hmm. Using dup2(probe, probe) to test if the new (high) fd itself has not been
> allocated?
fcntl(F_DUPFD[_CLOEXEC]) is smarter than dup2/3, if you plan on
atomically guaranteeing a dup to a not-in-use fd.
Will dup'ing to a high fd violate assumptions of programs that assume
that open() and friends favor the next available fd by default, rather
than having a gap? (Probably not, but skipping fds is not usual, so
it's worth asking.)
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
next prev parent reply other threads:[~2018-02-13 16:38 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-28 22:15 [Qemu-devel] [PATCH] linux-user: Use *at functions to implement interp_prefix Richard Henderson
2018-01-28 22:20 ` no-reply
2018-02-13 12:12 ` Peter Maydell
2018-02-13 15:31 ` Richard Henderson
2018-02-13 16:38 ` Eric Blake [this message]
2018-02-13 16:43 ` Peter Maydell
2018-02-13 16:50 ` Peter Maydell
2018-02-13 17:22 ` Richard Henderson
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