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bug#11443: linux "cp" and ocfs2 reflink/clone/fastcopy/copy on write
From: |
Kai Petzke |
Subject: |
bug#11443: linux "cp" and ocfs2 reflink/clone/fastcopy/copy on write |
Date: |
Wed, 9 May 2012 16:28:27 +0200 (CEST) |
User-agent: |
Alpine 2.00 (LNX 1167 2008-08-23) |
Hello,
there has been work by others about adding support for the OCFS2 "reflink"
ioctl() call, which is similiar to the btrfs "clone" call, and creates a
copy-on-write copy of the original, thus allowing to "copy" even gigabyte
sized files within a tiny fraction of a second, and without using much
additional file system space. See:
http://lists.gnu.org/archive/html/coreutils/2011-08/msg00046.html
http://lists.gnu.org/archive/html/bug-coreutils/2010-04/msg00185.html
I have updated those patches to work against coreutils 8.16, removed those
bugs, that I spotted. In particular, if the destination file exists, the
"reflink" ist automatically tried again after removing it, and if not all
attributes are copied, it is made sure, that the following open() system
call does not truncate the just created copy.
I strongly suggest including that patch in the coreutils package, even
though the interface to use to different system calls to achieve the same
thing is awkward. But, as laid out in the comments in the source, btrfs
clone and ocfs2 reflink are semantically quite different, so that unifying
them into one on the kernel side is not likely to happen, soon, if it
happens at all. If users don't use the --reflink option of "cp", the
additional code makes no difference, so it doesn't hurt. And if users use
"--reflink" on either of the supported file systems, they get a huge
advantage out of it!
Greetings
Kai Petzke
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coreutils-8.16-ocfs2-reflink.diff
Description: Text Data
- bug#11443: linux "cp" and ocfs2 reflink/clone/fastcopy/copy on write,
Kai Petzke <=