[Bug-tar] [PATCH] Re: Detection of sparse files is broken on btrfs

[Pavel Raiskup]

On Monday, January 8, 2018 3:29:17 AM CET Mark H Weaver wrote:
> I propose that we revisit this bug and fix it.  We clearly cannot assume that
> st_blocks == 0 implies that the file contains only zeroes.

. only on btrfs, as far as we know, because of some race condition.  So
what about special casing that filesystem, where we can lseek() for holes
anyway?  Since I would prefer fixing btrfs, I'm CC'ing devels again.

I'm attaching tar patch (public domain, use as you wish) mostly for
discussion about the idea (I can or anybody finalize the ifdef-hell,
etc.).  Note this fixes the failing sparse03.at for me (Fedora 27 x86_64 +
btrfs).

references for btrfs guys:
https://www.mail-archive.com/address@hidden/msg05453.html
https://www.spinics.net/lists/linux-btrfs/msg56768.html

Pavel

btrfs-wholesparse.patch
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