Re: [Qemu-devel] hd-geo-test creates 4GB files on FSes that don't support sparse images, doesn't delete them on error

[Eric Blake <eblake@redhat.com>]

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On 08/27/2015 09:17 AM, Peter Maydell wrote:
> I've noticed recently that tests/hd-geo-test.c creates test disk
> images which are 4GB in size, which is a problem if the filesystem
> on the host doesn't support sparse files. In particular, OSX's HFS+
> doesn't have sparse file support, and Windows probably doesn't either.

Windows NTFS supports sparse files (minimum hole size of 64k), but it
can be a pain to set up, and while it saves disk space, it may actually
slow your program down.

[At one point cygwin created sparse files on windows by default, but
because it was demonstrated to hurt performance in dealing with sparse
files, because Windows doesn't handle sparse files efficiently, the
cygwin defaults were switched so that it now requires an explicit opt-in
mount option before even attempting sparse files]

> Worse, if the test fails an assertion somewhere the test doesn't
> clean up after itself and leaves a 4GB file lying around in /tmp/.
> 
> It would be nice if we could skip these tests on filesystems that
> don't have sparse file support...

Or even where sparse files are supported but not default.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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