On 3/22/23 12:00 PM, Johannes Schindelin via GitGitGadget wrote:
From: Johannes Schindelin <johannes.schindelin@xxxxxx>
When a split-index is in effect, the `$GIT_DIR/index` file needs to
contain a "link" extension that contains all the information about the
split-index, including the information about the shared index.
However, in some cases Git needs to suppress writing that "link"
extension (i.e. to fall back to writing a full index) even if the
in-memory index structure _has_ a `split_index` configured. This is the
case e.g. when "too many not shared" index entries exist.
In such instances, the current code sets the `base_oid` field of said
`split_index` structure to all-zero to indicate that `do_write_index()`
should skip writing the "link" extension.
This can lead to problems later on, when the in-memory index is still
used to perform other operations and eventually wants to write a
split-index, detects the presence of the `split_index` and reuses that,
too (under the assumption that it has been initialized correctly and
still has a non-null `base_oid`).
Let's stop zeroing out the `base_oid` to indicate that the "link"
extension should not be written.
One might be tempted to simply call `discard_split_index()` instead,
under the assumption that Git decided to write a non-split index and
therefore the the `split_index` structure might no longer be wanted.
However, that is not possible because that would release index entries
in `split_index->base` that are likely to still be in use. Therefore we
cannot do that.
The next best thing we _can_ do is to introduce a flag, specifically
indicating when the "link" extension should be skipped. So that's what
we do here.
Signed-off-by: Johannes Schindelin <johannes.schindelin@xxxxxx>
---
read-cache.c | 37 ++++++++++++++++++++++--------------
t/t7527-builtin-fsmonitor.sh | 2 +-
2 files changed, 24 insertions(+), 15 deletions(-)
diff --git a/read-cache.c b/read-cache.c
index b09128b1884..8fcb2d54c05 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2868,6 +2868,12 @@ static int record_ieot(void)
return !git_config_get_index_threads(&val) && val != 1;
}
+enum strip_extensions {
+ WRITE_ALL_EXTENSIONS = 0,
+ STRIP_ALL_EXTENSIONS = 1,
+ STRIP_LINK_EXTENSION_ONLY = 2
+};
Earlier (in a response to Junio's response on this commit) I said
that I didn't think we needed to make a bit set here, but I want
to re-think that or at least walk thru the change and talk out loud.
I'll explain in-line below.
+
/*
* On success, `tempfile` is closed. If it is the temporary file
* of a `struct lock_file`, we will therefore effectively perform
@@ -2876,7 +2882,7 @@ static int record_ieot(void)
* rely on it.
*/
static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
- int strip_extensions, unsigned flags)
+ enum strip_extensions strip_extensions, unsigned flags)
{
uint64_t start = getnanotime();
struct hashfile *f;
@@ -3045,7 +3051,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
return -1;
}
- if (!strip_extensions && istate->split_index &&
+ if (strip_extensions == WRITE_ALL_EXTENSIONS && istate->split_index &&
!is_null_oid(&istate->split_index->base_oid)) {
(I hate all of this double negative logic...)
Here we only want the extension if we have WRITE_ALL, so that is
NOT STRIP_ALL and NOT STRIP_LINK_ONLY, so that is OK.
struct strbuf sb = STRBUF_INIT;
@@ -3060,7 +3066,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
if (err)
return -1;
}
- if (!strip_extensions && !drop_cache_tree && istate->cache_tree) {
+ if (strip_extensions != STRIP_ALL_EXTENSIONS && !drop_cache_tree && istate->cache_tree) {
Here we only want the extension when NOT STRIP_ALL, so this is
either WRITE_ALL or STRIP_LINK_ONLY, so this is OK. The rest are
the same, so I'll omit them.
[...]
All of this looks correct, but I stumbled over things on my first
or second reading. I wonder if it would it simplify things to define
this as:
enum strip_extensions {
WRITE_ALL_EXTENSIONS = 0,
STRIP_LINK_EXTENSION = (1<0),
STRIP_OTHER_EXTENSIONS = (1<1),
STRIP_ALL_EXTENSIONS = (STRIP_LINK_EXTENSION
| STRIP_OTHER_EXTENSIONS),
};
Then the link test becomes:
if ( ! (strip_extensions & STRIP_LINK_EXTENSION) &&
istate->split_index &&
...) {
and the others become:
if ( ! (strip_extensions & STRIP_OTHER_EXTENSIONS) &&
...) {
If we need to add the ability later to strip an individual,
we can easily add a bit to the enum and update the _ALL_ mask
and the corresponding `if` test.
In a later commit (probably in another series), we can invert
these double negatives to improve readability.
+/*
+ * Write the Git index into a `.lock` file
+ *
+ * If `strip_link_extension` is non-zero, avoid writing any "link" extension
+ * (used by the split-index feature).
+ */
static int do_write_locked_index(struct index_state *istate, struct lock_file *lock,
- unsigned flags)
+ unsigned flags, int strip_link_extension)
{
int ret;
int was_full = istate->sparse_index == INDEX_EXPANDED;
@@ -3185,7 +3197,7 @@ static int do_write_locked_index(struct index_state *istate, struct lock_file *l
*/
trace2_region_enter_printf("index", "do_write_index", the_repository,
"%s", get_lock_file_path(lock));
- ret = do_write_index(istate, lock->tempfile, 0, flags);
+ ret = do_write_index(istate, lock->tempfile, strip_link_extension ? STRIP_LINK_EXTENSION_ONLY : 0, flags);
trace2_region_leave_printf("index", "do_write_index", the_repository,
"%s", get_lock_file_path(lock));
@@ -3214,7 +3226,7 @@ static int write_split_index(struct index_state *istate,
{
int ret;
prepare_to_write_split_index(istate);
- ret = do_write_locked_index(istate, lock, flags);
+ ret = do_write_locked_index(istate, lock, flags, 0);
could we use the enum values here instead of 0 ?
finish_writing_split_index(istate);
return ret;
}
@@ -3366,9 +3378,7 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
if ((!si && !test_split_index_env) ||
alternate_index_output ||
(istate->cache_changed & ~EXTMASK)) {
- if (si)
- oidclr(&si->base_oid);
- ret = do_write_locked_index(istate, lock, flags);
+ ret = do_write_locked_index(istate, lock, flags, 1);
and here
goto out;
}
@@ -3394,8 +3404,7 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
/* Same initial permissions as the main .git/index file */
temp = mks_tempfile_sm(git_path("sharedindex_XXXXXX"), 0, 0666);
if (!temp) {
- oidclr(&si->base_oid);
- ret = do_write_locked_index(istate, lock, flags);
+ ret = do_write_locked_index(istate, lock, flags, 1);
and here
goto out;
}
ret = write_shared_index(istate, &temp, flags);
diff --git a/t/t7527-builtin-fsmonitor.sh b/t/t7527-builtin-fsmonitor.sh
index cbafdd69602..9fab9a2ab38 100755
--- a/t/t7527-builtin-fsmonitor.sh
+++ b/t/t7527-builtin-fsmonitor.sh
@@ -1003,7 +1003,7 @@ test_expect_success !UNICODE_COMPOSITION_SENSITIVE 'Unicode nfc/nfd' '
egrep "^event: nfd/d_${utf8_nfc}/?$" ./unicode.trace
'
-test_expect_failure 'split-index and FSMonitor work well together' '
+test_expect_success 'split-index and FSMonitor work well together' '
git init split-index &&
test_when_finished "git -C \"$PWD/split-index\" \
fsmonitor--daemon stop" &&
Thanks
Jeff
