On Sun, Jan 17, 2010 at 04:08:16PM +0100, Jim Meyering wrote:
> Michael Stone wrote:
> > It seems that touch -a does update ctime on btrfs, invalidating one of
> > the assumptions behind this test and causing it to fail.
>
> s/does/does not/
>
> Thanks for the report.
>
> I've just confirmed this test failure by building and running coreutils'
> "make check" on a btrfs file system I'd just created using mkfs.btrfs
> v0.19 on Fedora 12, btrfs-progs-0.19-9.fc12.x86_64
>
> However, it has nothing to do with touch, but rather looks
> like a bug (or at least a difference) in btrfs.
>
> Here's a function to provide a quick demo:
>
> ctime_vs_link_test() { env rm -f a b x; : > a; : > b; ln a x
> stat -f --pr '%T: ' .; case "$(env ls -ct a b)" in a*b) echo pass;; \
> *) echo fail; env stat --format='%n %z' a b;; esac; }
>
> Use it on a few file systems.
> This test passes on all I tried except btrfs:
> [note: $HOME is ext4]
>
> $ for i in $HOME/tmp /t /fs/btrfs /fs/xfs /fs/nilfs2; do
> cd $i && ctime_vs_link_test; done
> ext2/ext3: pass
> tmpfs: pass
> btrfs: fail
> a 2010-01-17 14:54:12.470194921 +0000
> b 2010-01-17 14:54:12.471193684 +0000
> xfs: pass
> nilfs2: pass
>
> In case it's not immediately obvious (time-stamp problems rarely are),
> here's a blow-by-blow:
>
> # After this, a's ctime precedes b's, even if just by ~1ms.
> rm -f a b x; : > a; : > b
>
> # Increasing a's link count must update its ctime to the present,
> # making it more recent than b's.
> ln a x
>
> # Sorting on ctime, a should come first:
> env ls -ct a b
Yeah its broken in F12 but it's fixed upstream. Thanks,
Josef
