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Re: [Qemu-devel] Heads up: glibc preadv emulation breaks qemu on older k

From: Anthony Liguori
Subject: Re: [Qemu-devel] Heads up: glibc preadv emulation breaks qemu on older kernels
Date: Fri, 12 Feb 2010 11:28:57 -0600
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20091209 Fedora/3.0-4.fc12 Lightning/1.0pre Thunderbird/3.0

On 02/12/2010 07:50 AM, Christoph Hellwig wrote:
On Fri, Feb 12, 2010 at 04:49:23PM +0300, malc wrote:
On Fri, 12 Feb 2010, Christoph Hellwig wrote:

On Thu, Feb 11, 2010 at 07:06:08PM +0000, Richard W.M. Jones wrote:
One interesting thing is that qemu has its own preadv emulation (which
does the emulation correctly), but this is never used because qemu
never gets ENOSYS back from preadv.
At this point the amount of bugs in the glibc preadv/pwritev code really
make me want to go to use the raw system calls on Linux only.  Any
opinions from the maintainers if that is acceptable?
There are more than one way to parse the first sentence, if it should be
read as:
   On linux and on linux only avoid using pread/write[v] and talk to the
   kernel directly.

Then i agree.
Yes.  The BSDs tend to not play stupid emulation games in the libc, so
changes of these kinds of messups to happen are far less.

In all fairness, I seem to recall there being a problem with the kernel implementation of preadv/pwritev too.

I think a configure option would be in order. Forever avoiding glibc is probably a bit extreme.


Anthony Liguori

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