Without this bug fix, t7519's four "status doesn't detect unreported
modifications" test cases would fail occasionally (and, oddly enough,
*a lot* more frequently on Windows).
The reason is that these test cases intentionally use the side effect of
`git status` to re-write the index if any updates were detected: they
first clean the worktree, run `git status` to update the index as well
as show the output to the casual reader, then make the worktree dirty
again and expect no changes to reported if running with a mocked
fsmonitor hook.
The problem with this strategy was that the index was written during
said `git status` on the clean worktree for the *wrong* reason: not
because the index was marked as changed (it wasn't), but because the
recorded mtimes were racy with the index' own mtime.
As the mtime granularity on Windows is 100 nanoseconds (see e.g.
https://docs.microsoft.com/en-us/windows/desktop/SysInfo/file-times),
the mtimes of the files are often enough *not* racy with the index', so
that that `git status` call currently does not always update the index
(including the fsmonitor extension), causing the test case to fail.
The obvious fix: if we change *any* index entry's `CE_FSMONITOR_VALID`
flag, we should also mark the index as changed. That will cause the
index to be written upon `git status`, *including* an updated fsmonitor
extension.
Side note: Even though the reader might think that the t7519 issue
should be *much* more prevalent on Linux, given that the ext4 filesystem
(that seems to be used by every Linux distribution) stores mtimes in
nanosecond precision. However, ext4 uses `current_kernel_time()` (see
https://unix.stackexchange.com/questions/11599#comment762968_11599; it
is *amazingly* hard to find any proper source of information about such
ext4 questions) whose accuracy seems to depend on many factors but is
safely worse than the 100-nanosecond granularity of NTFS (again, it is
*horribly* hard to find anything remotely authoritative about this
question). So it seems that the racy index condition that hid the bug
fixed by this patch simply is a lot more likely on Linux than on
Windows. But not impossible ;-)
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Git - fast, scalable, distributed revision control system
Git is a fast, scalable, distributed revision control system with an
unusually rich command set that provides both high-level operations
and full access to internals.
Git is an Open Source project covered by the GNU General Public
License version 2 (some parts of it are under different licenses,
compatible with the GPLv2). It was originally written by Linus
Torvalds with help of a group of hackers around the net.
Please read the file INSTALL for installation instructions.
Many Git online resources are accessible from https://git-scm.com/
including full documentation and Git related tools.
See Documentation/gittutorial.txt to get started, then see
Documentation/giteveryday.txt for a useful minimum set of commands, and
Documentation/git-.txt for documentation of each command.
If git has been correctly installed, then the tutorial can also be
read with man gittutorial or git help tutorial, and the
documentation of each command with man git-<commandname> or git help <commandname>.
CVS users may also want to read Documentation/gitcvs-migration.txt
(man gitcvs-migration or git help cvs-migration if git is
installed).
Issues which are security relevant should be disclosed privately to
the Git Security mailing list git-security@googlegroups.com.
The maintainer frequently sends the "What's cooking" reports that
list the current status of various development topics to the mailing
list. The discussion following them give a good reference for
project status, development direction and remaining tasks.
The name "git" was given by Linus Torvalds when he wrote the very
first version. He described the tool as "the stupid content tracker"
and the name as (depending on your mood):
random three-letter combination that is pronounceable, and not
actually used by any common UNIX command. The fact that it is a
mispronunciation of "get" may or may not be relevant.
stupid. contemptible and despicable. simple. Take your pick from the
dictionary of slang.
"global information tracker": you're in a good mood, and it actually
works for you. Angels sing, and a light suddenly fills the room.
"goddamn idiotic truckload of sh*t": when it breaks
