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Re: [Qemu-devel] [PATCH v4 7/7] osdep: Enable qemu_open to dup pre-opene

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v4 7/7] osdep: Enable qemu_open to dup pre-opened fd
Date: Mon, 25 Jun 2012 08:34:47 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120605 Thunderbird/13.0

On 06/25/2012 08:24 AM, Corey Bryant wrote:

>>> +            if (fcntl_setfl(ret, O_CLOEXEC, (flags & O_CLOEXEC) ? 1
>>> : 0) < 0) {
>> Broken.  O_CLOEXEC _only_ affects open(); to change it on an existing
>> fd, you have to use fcntl(F_GETFD/F_SETFD) (not F_GETFL/F_SETFL).
> I'll fix this in v5.

Don't we already have qemu_set_cloexec() for this purpose?

> I see your point.  I'll call fcntl(F_GETFL) once to get the current
> flags, determine what needs to be set on/off, and then call
> fnctl(F_SETFL) once.  In this case I won't be using fcntl_setfl()
> anymore.  Do you want me to drop the fcntl_setfl() changes I made?

Or maybe make fcntl_setfl() take a mask of bits to alter?  You're right
that it's not worth changing if you won't take advantage of the changes.

> Also, I noticed in the fnctl man page that F_SETFL:  "On Linux this
> command can change only the O_APPEND, O_ASYNC, O_DIRECT, O_NOATIME, and
> O_NONBLOCK flags."  So I'll only set/unset these flags.

O_NDELAY is the obsolete spelling of O_NONBLOCK; which means the only
other flags in your list not supported by Linux are O_LARGEFILE (which I
said was pointless), O_NOCTTY (which only has an impact at open() and
not later on, so it is not worth worrying about), and O_SYNC (so for
that one, you should error out if not set correctly, as the difference
between O_SYNC on vs. off is significant).

Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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