From: Paul Brook <paul@codesourcery.com>
To: qemu-devel@nongnu.org
Cc: Anthony Liguori <anthony@codemonkey.ws>,
Blue Swirl <blauwirbel@gmail.com>,
markmc@redhat.com, kvm@vger.kernel.org
Subject: Re: [Qemu-devel] [PATCH v2 6/8] qemu:virtio-net: Enable filtering based on MAC, promisc, broadcast and allmulti
Date: Tue, 3 Feb 2009 23:35:46 +0000 [thread overview]
Message-ID: <200902032335.48083.paul@codesourcery.com> (raw)
In-Reply-To: <4988AECB.2070208@codemonkey.ws>
> >> + static uint8_t bcast[] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff};
> >
> > 'const'?
>
> It may be good practice but practically speaking, I don't think it will
> generate different code. The only thing that uses bcast is memcmp()
> which should be a builtin. Since bcast doesn't otherwise escape the
> function, it's an obvious candidate for optimization. I think the
> compiler already has enough information that const doesn't tell it
> anything more.
const is as much for the programmer as the compiler[1]. Modifying this
variable is just plain wrong, so it's a good idea to let the compiler enforce
that.
Paul
[1] In many cases (especially when combined with pointers) "const" doesn't
actually mean what may people think it does. Ask your local C language expert
if you don't know what I'm talking about.
WARNING: multiple messages have this Message-ID (diff)
From: Paul Brook <paul@codesourcery.com>
To: qemu-devel@nongnu.org
Cc: Blue Swirl <blauwirbel@gmail.com>,
markmc@redhat.com, kvm@vger.kernel.org
Subject: Re: [Qemu-devel] [PATCH v2 6/8] qemu:virtio-net: Enable filtering based on MAC, promisc, broadcast and allmulti
Date: Tue, 3 Feb 2009 23:35:46 +0000 [thread overview]
Message-ID: <200902032335.48083.paul@codesourcery.com> (raw)
In-Reply-To: <4988AECB.2070208@codemonkey.ws>
> >> + static uint8_t bcast[] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff};
> >
> > 'const'?
>
> It may be good practice but practically speaking, I don't think it will
> generate different code. The only thing that uses bcast is memcmp()
> which should be a builtin. Since bcast doesn't otherwise escape the
> function, it's an obvious candidate for optimization. I think the
> compiler already has enough information that const doesn't tell it
> anything more.
const is as much for the programmer as the compiler[1]. Modifying this
variable is just plain wrong, so it's a good idea to let the compiler enforce
that.
Paul
[1] In many cases (especially when combined with pointers) "const" doesn't
actually mean what may people think it does. Ask your local C language expert
if you don't know what I'm talking about.
next prev parent reply other threads:[~2009-02-03 23:35 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-03 19:29 [PATCH v2 0/8] qemu:virtio-net: Add MAC and VLAN filtering Alex Williamson
2009-02-03 19:29 ` [Qemu-devel] " Alex Williamson
2009-02-03 19:29 ` [PATCH v2 1/8] qemu:virtio-net: Save status and add some save infrastructure Alex Williamson
2009-02-03 19:29 ` [Qemu-devel] " Alex Williamson
2009-02-03 19:29 ` [PATCH v2 2/8] qemu:virtio-net: Allow setting the MAC address via set_config Alex Williamson
2009-02-03 19:29 ` [Qemu-devel] " Alex Williamson
2009-02-03 19:29 ` [PATCH v2 3/8] qemu:virtio-net: Define ETH_ALEN for use when manipulating MAC addresses Alex Williamson
2009-02-03 19:29 ` [Qemu-devel] " Alex Williamson
2009-02-03 19:29 ` [PATCH v2 4/8] qemu:virtio-net: Add a virtqueue for control commands from the guest Alex Williamson
2009-02-03 19:29 ` [Qemu-devel] " Alex Williamson
2009-02-03 20:56 ` Anthony Liguori
2009-02-03 20:56 ` [Qemu-devel] " Anthony Liguori
2009-02-04 22:59 ` Alex Williamson
2009-02-04 22:59 ` [Qemu-devel] " Alex Williamson
2009-02-04 23:09 ` malc
2009-02-04 23:09 ` malc
2009-02-04 23:34 ` Alex Williamson
2009-02-04 23:14 ` Anthony Liguori
2009-02-04 23:14 ` [Qemu-devel] " Anthony Liguori
2009-02-03 19:29 ` [PATCH v2 5/8] qemu:virtio-net: Add promiscuous and all-multicast mode bits Alex Williamson
2009-02-03 19:29 ` [Qemu-devel] " Alex Williamson
2009-02-03 19:30 ` [PATCH v2 6/8] qemu:virtio-net: Enable filtering based on MAC, promisc, broadcast and allmulti Alex Williamson
2009-02-03 19:30 ` [Qemu-devel] " Alex Williamson
2009-02-03 20:06 ` Blue Swirl
2009-02-03 20:06 ` Blue Swirl
2009-02-03 20:53 ` Anthony Liguori
2009-02-03 20:53 ` Anthony Liguori
2009-02-03 23:35 ` Paul Brook [this message]
2009-02-03 23:35 ` Paul Brook
2009-02-04 0:18 ` malc
2009-02-04 0:18 ` [Qemu-devel] " malc
2009-02-03 19:30 ` [PATCH v2 7/8] qemu:virtio-net: Add additional MACs via a filter table Alex Williamson
2009-02-03 19:30 ` [Qemu-devel] " Alex Williamson
2009-02-03 19:30 ` [PATCH v2 8/8] qemu:virtio-net: Add VLAN filtering Alex Williamson
2009-02-03 19:30 ` [Qemu-devel] " Alex Williamson
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