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From: Peter Maydell <peter.maydell@linaro.org>
Date: Sat, 8 Sep 2018 16:34:36 +0100
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Subject: Re: [Qemu-devel] [PATCH] block/file-posix: fix the wrong result of
 find_allocation() in macOS.
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To: Yan-Jie Wang <jaywang0.tw@gmail.com>
Cc: QEMU Developers <qemu-devel@nongnu.org>, qemu-stable <qemu-stable@nongnu.org>

On 8 September 2018 at 15:15, Yan-Jie Wang <jaywang0.tw@gmail.com> wrote:
> In macOS, lseek with SEEK_DATA behaves differently.
> It seeks to the next data region even though offset is in the middle of
> a data region. In addition, there may be many data regions without any
> hole among them, like this: |---Data---|---Data---|
>
> Because of this, qemu-img convert with raw images as input may create
> corrupted images in macOS especially for large files, and qemu-img
> map may also report wrong things. This patch fixes this undesired
> behaviors.

Hi. I have two general questions here:
(1) is this behaviour of SEEK_DATA specific to macOS, or do the
other BSDs (FreeBSD, OpenBSD, NetBSD) also have it ?
(2) is there a way to determine which flavour of SEEK_DATA we
have as a configure-time test rather than having to hardcode
an OS-specific #ifdef ?

thanks
-- PMM