On 04/15/2011 11:16 AM, Christoph Hellwig wrote: > On Fri, Apr 15, 2011 at 10:53:48AM +0200, Jim Meyering wrote: >> Can you or anyone else point to authoritative documentation >> (or even a summary of those "discussions") of FIEMAP semantics? > > A large part of the problem is that there's none and the semantics > is a hode-podge of random flags that mostly make little sense > outside of fs developers debugging the layout that we created. The > closest to a description is Documentation/filesystems/fiemap.txt > in the kernel tree, but that doesn't document most of the delicate > points. Would it be worth borrowing from Solaris' semantics and adding SEEK_HOLE and SEEK_DATA to lseek(2), as a higher level (less-detailed, but easier to define and easier to use) interface for discovering the regions of a file that only contain NUL bytes? FIEMAP is a great interface at exposing everything possible, but coreutils doesn't necessarily need all that complexity just for determining when it is safe to skip over a portion of a file that is either unallocated or unchanged from the initial 0 contents. -- Eric Blake eblake@xxxxxxxxxx +1-801-349-2682 Libvirt virtualization library http://libvirt.org
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