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fsmonitor: handle shortname for .git
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On Windows, teach FSMonitor to recognize the shortname of ".git"
as an alias for ".git".

Sometimes we receive FS events using the shortname, such as when
a CMD shell runs "RENAME GIT~1 FOO" or "RMDIR GIT~1".  The FS
notification arrives using whatever combination of long and
shortnames used by the other process.  (Shortnames do seem to
be case normalized, however.)

NEEDSWORK: This only addresses the case of removing or renaming
the ".git" directory using the shortname alias, so that the daemon
properly shuts down.  I'm leaving it a task for later to handle
the general case of shortnames and report them to the fsmonitor
client process.  This would include tracked and untracked paths
that just happen to have a shortname alias.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
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@jeffhostetler @dscho
jeffhostetler authored and dscho committed Aug 16, 2021
1 parent 27846cc commit 0fadc91
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Showing 2 changed files with 217 additions and 40 deletions.
192 changes: 152 additions & 40 deletions compat/fsmonitor/fsm-listen-win32.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -48,6 +48,8 @@ struct fsmonitor_daemon_backend_data
#define LISTENER_HAVE_DATA_WORKTREE 1
#define LISTENER_HAVE_DATA_GITDIR 2
int nr_listener_handles;

struct strbuf dot_git_shortname;
};

/*
Expand Down Expand Up @@ -258,6 +260,62 @@ static void cancel_rdcw_watch(struct one_watch *watch)
watch->is_active = FALSE;
}

/*
* Process a single relative pathname event.
* Return 1 if we should shutdown.
*/
static int process_1_worktree_event(
FILE_NOTIFY_INFORMATION *info,
struct string_list *cookie_list,
struct fsmonitor_batch **batch,
const struct strbuf *path,
enum fsmonitor_path_type t)
{
const char *slash;

switch (t) {
case IS_INSIDE_DOT_GIT_WITH_COOKIE_PREFIX:
/* special case cookie files within .git */

/* Use just the filename of the cookie file. */
slash = find_last_dir_sep(path->buf);
string_list_append(cookie_list,
slash ? slash + 1 : path->buf);
break;

case IS_INSIDE_DOT_GIT:
/* ignore everything inside of "<worktree>/.git/" */
break;

case IS_DOT_GIT:
/* "<worktree>/.git" was deleted (or renamed away) */
if ((info->Action == FILE_ACTION_REMOVED) ||
(info->Action == FILE_ACTION_RENAMED_OLD_NAME)) {
trace2_data_string("fsmonitor", NULL,
"fsm-listen/dotgit",
"removed");
return 1;
}
break;

case IS_WORKDIR_PATH:
/* queue normal pathname */
if (!*batch)
*batch = fsmonitor_batch__new();
fsmonitor_batch__add_path(*batch, path->buf);
break;

case IS_GITDIR:
case IS_INSIDE_GITDIR:
case IS_INSIDE_GITDIR_WITH_COOKIE_PREFIX:
default:
BUG("unexpected path classification '%d' for '%s'",
t, path->buf);
}

return 0;
}

/*
* Process filesystem events that happen anywhere (recursively) under the
* <worktree> root directory. For a normal working directory, this includes
Expand Down Expand Up @@ -302,7 +360,6 @@ static int process_worktree_events(struct fsmonitor_daemon_state *state)
*/
for (;;) {
FILE_NOTIFY_INFORMATION *info = (void *)p;
const char *slash;
enum fsmonitor_path_type t;

strbuf_reset(&path);
Expand All @@ -311,45 +368,45 @@ static int process_worktree_events(struct fsmonitor_daemon_state *state)

t = fsmonitor_classify_path_workdir_relative(path.buf);

switch (t) {
case IS_INSIDE_DOT_GIT_WITH_COOKIE_PREFIX:
/* special case cookie files within .git */

/* Use just the filename of the cookie file. */
slash = find_last_dir_sep(path.buf);
string_list_append(&cookie_list,
slash ? slash + 1 : path.buf);
break;

case IS_INSIDE_DOT_GIT:
/* ignore everything inside of "<worktree>/.git/" */
break;

case IS_DOT_GIT:
/* "<worktree>/.git" was deleted (or renamed away) */
if ((info->Action == FILE_ACTION_REMOVED) ||
(info->Action == FILE_ACTION_RENAMED_OLD_NAME)) {
trace2_data_string("fsmonitor", NULL,
"fsm-listen/dotgit",
"removed");
goto force_shutdown;
}
break;

case IS_WORKDIR_PATH:
/* queue normal pathname */
if (!batch)
batch = fsmonitor_batch__new();
fsmonitor_batch__add_path(batch, path.buf);
break;

case IS_GITDIR:
case IS_INSIDE_GITDIR:
case IS_INSIDE_GITDIR_WITH_COOKIE_PREFIX:
default:
BUG("unexpected path classification '%d' for '%s'",
t, path.buf);
}
if (process_1_worktree_event(info, &cookie_list, &batch,
&path, t))
goto force_shutdown;

/*
* NEEDSWORK: If `path` contains a shortname (that is,
* if any component within it is a shortname), we
* should expand it to a longname (See
* `GetLongPathNameW()`) and re-normalize, classify,
* and process it because our client is probably
* expecting "normal" paths.
*
* HOWEVER, if our process has called `chdir()` to get
* us out of the root of the worktree (so that the
* root directory is not busy), then we have to be
* careful to convert the paths in the INFO array
* (which are relative to the directory of the RDCW
* watch and not the CWD) into absolute paths before
* calling GetLongPathNameW() and then convert the
* computed value back to a RDCW-relative pathname
* (which is what we and the client expect).
*
* FOR NOW, just handle case (1) exactly so that we
* shutdown properly when ".git" is deleted via the
* shortname alias.
*
* We might see case (2) events for cookie files, but
* we can ignore them.
*
* FOR LATER, handle case (3) where the worktree
* events contain shortnames. We should convert
* them to longnames to avoid confusing the client.
*/
if (data->dot_git_shortname.len &&
!strcmp(path.buf, data->dot_git_shortname.buf) &&
process_1_worktree_event(info, &cookie_list, &batch,
&data->dot_git_shortname,
IS_DOT_GIT))
goto force_shutdown;

skip_this_path:
if (!info->NextEntryOffset)
Expand Down Expand Up @@ -423,6 +480,14 @@ static int process_gitdir_events(struct fsmonitor_daemon_state *state)
t, path.buf);
}

/*
* WRT shortnames, this external gitdir will not see
* case (1) nor case (3) events.
*
* We might see case (2) events for cookie files, but
* we can ignore them.
*/

skip_this_path:
if (!info->NextEntryOffset)
break;
Expand Down Expand Up @@ -524,6 +589,7 @@ void fsm_listen__loop(struct fsmonitor_daemon_state *state)
int fsm_listen__ctor(struct fsmonitor_daemon_state *state)
{
struct fsmonitor_daemon_backend_data *data;
char shortname[16]; /* a padded 8.3 buffer */

CALLOC_ARRAY(data, 1);

Expand Down Expand Up @@ -554,6 +620,52 @@ int fsm_listen__ctor(struct fsmonitor_daemon_state *state)
data->nr_listener_handles++;
}

/*
* NEEDSWORK: Properly handle 8.3 shortnames. RDCW events can
* contain a shortname (if another application uses a
* shortname in a system call). We care about aliasing and
* the use of shortnames for:
*
* (1) ".git",
* -- if an external process deletes ".git" using "GIT~1",
* we need to catch that and shutdown.
*
* (2) our cookie files,
* -- if an external process deletes one of our cookie
* files using a shortname, we will get a shortname
* event for it. However, we should have already
* gotten a longname event for it when we created the
* cookie, so we can safely discard the shortname
* events for cookie files.
*
* (3) the spelling of modified files that we report to clients.
* -- we need to report the longname to the client because
* that is what they are expecting. Presumably, the
* client is going to lookup the paths that we report
* in their index and untracked-cache, so we should
* normalize the data for them. (Technically, they
* could adapt, so we could relax this maybe.)
*
* FOR NOW, while our CWD is at the root of the worktree we
* can easily get the spelling of the shortname of ".git" (if
* the volume has shortnames enabled). For most worktrees
* this value will be "GIT~1", but we don't want to assume
* that.
*
* Capture this so that we can handle (1).
*
* We leave (3) for a future effort.
*/
strbuf_init(&data->dot_git_shortname, 0);
GetShortPathNameA(".git", shortname, sizeof(shortname));
if (!strcmp(".git", shortname))
trace_printf_key(&trace_fsmonitor, "No shortname for '.git'");
else {
trace_printf_key(&trace_fsmonitor,
"Shortname of '.git' is '%s'", shortname);
strbuf_addstr(&data->dot_git_shortname, shortname);
}

state->backend_data = data;
return 0;

Expand Down
65 changes: 65 additions & 0 deletions t/t7527-builtin-fsmonitor.sh
View file
Original file line number Diff line number Diff line change
Expand Up @@ -123,6 +123,71 @@ test_expect_success 'implicit daemon stop (rename .git)' '
test_must_fail git -C test_implicit_2 fsmonitor--daemon status
'

# File systems on Windows may or may not have shortnames.
# This is a volume-specific setting on modern systems.
# "C:/" drives are required to have them enabled. Other
# hard drives default to disabled.
#
# This is a crude test to see if shortnames are enabled
# on the volume containing the test directory. It is
# crude, but it does not require elevation like `fsutil`.
#
test_lazy_prereq SHORTNAMES '
mkdir .foo &&
test -d "FOO~1"
'

# Here we assume that the shortname of ".git" is "GIT~1".
test_expect_success MINGW,SHORTNAMES 'implicit daemon stop (rename GIT~1)' '
test_when_finished "stop_daemon_delete_repo test_implicit_1s" &&
git init test_implicit_1s &&
start_daemon test_implicit_1s &&
# renaming the .git directory will implicitly stop the daemon.
# this moves {.git, GIT~1} to {.gitxyz, GITXYZ~1}.
# the rename-from FS Event will contain the shortname.
#
mv test_implicit_1s/GIT~1 test_implicit_1s/.gitxyz &&
sleep 1 &&
# put it back so that our status will not crawl out to our
# parent directory.
# this moves {.gitxyz, GITXYZ~1} to {.git, GIT~1}.
mv test_implicit_1s/.gitxyz test_implicit_1s/.git &&
test_must_fail git -C test_implicit_1s fsmonitor--daemon status
'

# Here we first create a file with LONGNAME of "GIT~1" before
# we create the repo. This will cause the shortname of ".git"
# to be "GIT~2".
test_expect_success MINGW,SHORTNAMES 'implicit daemon stop (rename GIT~2)' '
test_when_finished "stop_daemon_delete_repo test_implicit_1s2" &&
mkdir test_implicit_1s2 &&
echo HELLO >test_implicit_1s2/GIT~1 &&
git init test_implicit_1s2 &&
test_path_is_file test_implicit_1s2/GIT~1 &&
test_path_is_dir test_implicit_1s2/GIT~2 &&
start_daemon test_implicit_1s2 &&
# renaming the .git directory will implicitly stop the daemon.
# the rename-from FS Event will contain the shortname.
#
mv test_implicit_1s2/GIT~2 test_implicit_1s2/.gitxyz &&
sleep 1 &&
# put it back so that our status will not crawl out to our
# parent directory.
mv test_implicit_1s2/.gitxyz test_implicit_1s2/.git &&
test_must_fail git -C test_implicit_1s2 fsmonitor--daemon status
'

test_expect_success 'cannot start multiple daemons' '
test_when_finished "stop_daemon_delete_repo test_multiple" &&
Expand Down

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