Let's start with the commit message of [1] from freebsd.git [2]
Sync timestamp changes for inodes of special files to disk as late
as possible (when the inode is reclaimed). Temporarily only do
this if option UFS_LAZYMOD configured and softupdates aren't
enabled. UFS_LAZYMOD is intentionally left out of
/sys/conf/options.
This is mainly to avoid almost useless disk i/o on battery powered
machines. It's silly to write to disk (on the next sync or when
the inode becomes inactive) just because someone hit a key or
something wrote to the screen or /dev/null.
PR: 5577 [3]
The short version of that, in the context of t7063, is that when a
directory is updated, its mtime may be updated later, not
immediately. This can be shown with a simple command sequence
date; sleep 1; touch abc; rm abc; sleep 10; ls -lTd .
One would expect that the date shown in `ls` would be one second from
`date`, but it's 10 seconds later. If we put another `ls -lTd .` in
front of `sleep 10`, then the date of the last `ls` comes as
expected. The first `ls` somehow forces mtime to be updated.
t7063 is really sensitive to directory mtime. When mtime is too "new",
git code suspects racy timestamps and will not trigger the shortcut in
untracked cache, in t7063.26 (or t7063.25 before this patch) and
eventually be detected in t7063.28
We have two options thanks to this special FreeBSD feature:
1) Stop supporting untracked cache on FreeBSD. Skip t7063 entirely
when running on FreeBSD
2) Work around this problem (using the same 'ls' trick) and continue
to support untracked cache on FreeBSD
I initially wanted to go with 1) because I didn't know the exact
nature of this feature and feared that it would make untracked cache
work unreliably, using the cached version when it should not.
Since the behavior of this thing is clearer now. The picture is not
that bad. If this indeed happens often, untracked cache would assume
racy condition more often and _fall back_ to non-untracked cache code
paths. Which means it may be less effective, but it will not show
wrong things.
This patch goes with option 2.
PS. For those who want to look further in FreeBSD source code, this
flag is now called IN_LAZYMOD. I can see it's effective in ext2 and
ufs. zfs is questionable.
[1] 660e6408e6df99a20dacb070c5e7f9739efdf96d
[2] git://github.com/freebsd/freebsd.git
[3] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=5577
Reported-by: Eric Wong <e@xxxxxxxxx>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx>
---
This is only of those commits that commit messages are more important
than the patch itself. One of the good notes about directory mtime,
if we start to use it in more places in git.
t/t7063-status-untracked-cache.sh | 4 ++++
t/test-lib.sh | 6 ++++++
2 files changed, 10 insertions(+)
diff --git a/t/t7063-status-untracked-cache.sh b/t/t7063-status-untracked-cache.sh
index a971884..08fc586 100755
--- a/t/t7063-status-untracked-cache.sh
+++ b/t/t7063-status-untracked-cache.sh
@@ -419,6 +419,10 @@ test_expect_success 'create/modify files, some of which are gitignored' '
rm base
'
+test_expect_success FREEBSD 'Work around lazy mtime update' '
+ ls -ld . >/dev/null
+'
+
test_expect_success 'test sparse status with untracked cache' '
: >../trace &&
avoid_racy &&
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 0055ebb..3c730a2 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -961,6 +961,12 @@ case $(uname -s) in
test_set_prereq SED_STRIPS_CR
test_set_prereq GREP_STRIPS_CR
;;
+*FreeBSD*)
+ test_set_prereq FREEBSD
+ test_set_prereq POSIXPERM
+ test_set_prereq BSLASHPSPEC
+ test_set_prereq EXECKEEPSPID
+ ;;
*)
test_set_prereq POSIXPERM
test_set_prereq BSLASHPSPEC
--
2.9.1.566.gbd532d4
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