On 01/21/2013 10:52 AM, Eric Blake wrote: > On 01/21/2013 10:03 AM, Kevin Wolf wrote: >> Am 21.01.2013 17:27, schrieb Eric Blake: >>> On 01/21/2013 07:25 AM, Federico Simoncelli wrote: >>>> This patch adds the support for reporting the highest offset in use by >>>> an image. This is particularly useful after a conversion (or a rebase) >>>> where the destination is a block device in order to find the actual >>>> amount of space in use. > >>>> + if (result.highest_offset > 0) { >>>> + printf("Highest offset in use: %" PRId64 "\n", >>>> result.highest_offset); >>> >>> This output message feels off by one. Either you need to subtract 1 >>> from res->highest_offset to get the address of the last used byte, or >>> you need to document it as the first unused byte, or instead of calling >>> it 'highest offset', you should call it 'used bytes' (except that with >>> sparse files, it's hard to argue that all earlier bytes were 'used'). >> >> Good point. I think the number is what we wanted, and what users are >> interested in is probably "used bytes" rather than "first unused byte". >> Maybe we can find a better word for "used" (it has the same problem in >> all three contexts), but I can't think of one off the top of my head. > > "Allocation" alone isn't good (because of sparse files, not all earlier > bytes are allocated). But maybe "Offset of unallocated tail: ..." > works, to make it clear that there may be other unallocated portions > earlier, but that all bytes at the listed offset and beyond are > unallocated. For a file that is completely allocated, or even for a > sparse file but with no unallocated tail, the value would be the same as > the file capacity.
On IRC, we decided the name result.image_end_offset feels better. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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