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refs: selectively set prefix in the seek functions 

The ref iterator exposes a `ref_iterator_seek()` function. The name
suggests that this would seek the iterator to a specific reference in
some ways similar to how `fseek()` works for the filesystem.

However, the function actually sets the prefix for refs iteration. So
further iteration would only yield references which match the particular
prefix. This is a bit confusing.

Let's add a 'flags' field to the function, which when set with the
'REF_ITERATOR_SEEK_SET_PREFIX' flag, will set the prefix for the
iteration in-line with the existing behavior. Otherwise, the reference
backends will simply seek to the specified reference and clears any
previously set prefix. This allows users to start iteration from a
specific reference.

In the packed and reftable backend, since references are available in a
sorted list, the changes are simply setting the prefix if needed. The
changes on the files-backend are a little more involved, since the files
backend uses the 'ref-cache' mechanism. We move out the existing logic
within `cache_ref_iterator_seek()` to `cache_ref_iterator_set_prefix()`
which is called when the 'REF_ITERATOR_SEEK_SET_PREFIX' flag is set. We
then parse the provided seek string and set the required levels and
their indexes to ensure that seeking is possible.

Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
maint
Karthik Nayak 2025-07-15 13:28:28 +02:00 committed by Junio C Hamano
parent 883a7ea054
commit 2b4648b919
9 changed files with 152 additions and 50 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
refs.c
View File

@ -2666,12 +2666,12 @@ enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs
if (!initial_transaction) {
int ok;

if (!iter) {
if (!iter)
iter = refs_ref_iterator_begin(refs, dirname.buf, NULL, 0,
DO_FOR_EACH_INCLUDE_BROKEN);
} else if (ref_iterator_seek(iter, dirname.buf) < 0) {
else if (ref_iterator_seek(iter, dirname.buf,
REF_ITERATOR_SEEK_SET_PREFIX) < 0)
goto cleanup;
}

while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
if (skip &&

26
refs.h
View File

@ -1299,21 +1299,29 @@ struct ref_iterator *refs_ref_iterator_begin(
*/
int ref_iterator_advance(struct ref_iterator *ref_iterator);

enum ref_iterator_seek_flag {
/*
* When the REF_ITERATOR_SEEK_SET_PREFIX flag is set, the iterator's prefix is
* updated to match the provided string, affecting all subsequent iterations. If
* not, the iterator seeks to the specified reference and clears any previously
* set prefix.
*/
REF_ITERATOR_SEEK_SET_PREFIX = (1 << 0),
};

/*
* Seek the iterator to the first reference with the given prefix.
* The prefix is matched as a literal string, without regard for path
* separators. If prefix is NULL or the empty string, seek the iterator to the
* Seek the iterator to the first reference matching the given seek string.
* The seek string is matched as a literal string, without regard for path
* separators. If seek is NULL or the empty string, seek the iterator to the
* first reference again.
*
* This function is expected to behave as if a new ref iterator with the same
* prefix had been created, but allows reuse of iterators and thus may allow
* the backend to optimize. Parameters other than the prefix that have been
* passed when creating the iterator will remain unchanged.
* This function is expected to behave as if a new ref iterator has been
* created, but allows reuse of existing iterators for optimization.
*
* Returns 0 on success, a negative error code otherwise.
*/
int ref_iterator_seek(struct ref_iterator *ref_iterator,
const char *prefix);
int ref_iterator_seek(struct ref_iterator *ref_iterator, const char *refname,
unsigned int flags);

/*
* If possible, peel the reference currently being viewed by the

7
refs/debug.c
View File

@ -170,12 +170,13 @@ static int debug_ref_iterator_advance(struct ref_iterator *ref_iterator)
}

static int debug_ref_iterator_seek(struct ref_iterator *ref_iterator,
const char *prefix)
const char *refname, unsigned int flags)
{
struct debug_ref_iterator *diter =
(struct debug_ref_iterator *)ref_iterator;
int res = diter->iter->vtable->seek(diter->iter, prefix);
trace_printf_key(&trace_refs, "iterator_seek: %s: %d\n", prefix ? prefix : "", res);
int res = diter->iter->vtable->seek(diter->iter, refname, flags);
trace_printf_key(&trace_refs, "iterator_seek: %s flags: %d: %d\n",
refname ? refname : "", flags, res);
return res;
}


7
refs/files-backend.c
View File

@ -929,11 +929,11 @@ static int files_ref_iterator_advance(struct ref_iterator *ref_iterator)
}

static int files_ref_iterator_seek(struct ref_iterator *ref_iterator,
const char *prefix)
const char *refname, unsigned int flags)
{
struct files_ref_iterator *iter =
(struct files_ref_iterator *)ref_iterator;
return ref_iterator_seek(iter->iter0, prefix);
return ref_iterator_seek(iter->iter0, refname, flags);
}

static int files_ref_iterator_peel(struct ref_iterator *ref_iterator,
@ -2316,7 +2316,8 @@ static int files_reflog_iterator_advance(struct ref_iterator *ref_iterator)
}

static int files_reflog_iterator_seek(struct ref_iterator *ref_iterator UNUSED,
const char *prefix UNUSED)
const char *refname UNUSED,
unsigned int flags UNUSED)
{
BUG("ref_iterator_seek() called for reflog_iterator");
}

26
refs/iterator.c
View File

@ -15,10 +15,10 @@ int ref_iterator_advance(struct ref_iterator *ref_iterator)
return ref_iterator->vtable->advance(ref_iterator);
}

int ref_iterator_seek(struct ref_iterator *ref_iterator,
const char *prefix)
int ref_iterator_seek(struct ref_iterator *ref_iterator, const char *refname,
unsigned int flags)
{
return ref_iterator->vtable->seek(ref_iterator, prefix);
return ref_iterator->vtable->seek(ref_iterator, refname, flags);
}

int ref_iterator_peel(struct ref_iterator *ref_iterator,
@ -57,7 +57,8 @@ static int empty_ref_iterator_advance(struct ref_iterator *ref_iterator UNUSED)
}

static int empty_ref_iterator_seek(struct ref_iterator *ref_iterator UNUSED,
const char *prefix UNUSED)
const char *refname UNUSED,
unsigned int flags UNUSED)
{
return 0;
}
@ -224,7 +225,7 @@ error:
}

static int merge_ref_iterator_seek(struct ref_iterator *ref_iterator,
const char *prefix)
const char *refname, unsigned int flags)
{
struct merge_ref_iterator *iter =
(struct merge_ref_iterator *)ref_iterator;
@ -234,11 +235,11 @@ static int merge_ref_iterator_seek(struct ref_iterator *ref_iterator,
iter->iter0 = iter->iter0_owned;
iter->iter1 = iter->iter1_owned;

ret = ref_iterator_seek(iter->iter0, prefix);
ret = ref_iterator_seek(iter->iter0, refname, flags);
if (ret < 0)
return ret;

ret = ref_iterator_seek(iter->iter1, prefix);
ret = ref_iterator_seek(iter->iter1, refname, flags);
if (ret < 0)
return ret;

@ -407,13 +408,16 @@ static int prefix_ref_iterator_advance(struct ref_iterator *ref_iterator)
}

static int prefix_ref_iterator_seek(struct ref_iterator *ref_iterator,
const char *prefix)
const char *refname, unsigned int flags)
{
struct prefix_ref_iterator *iter =
(struct prefix_ref_iterator *)ref_iterator;
free(iter->prefix);
iter->prefix = xstrdup_or_null(prefix);
return ref_iterator_seek(iter->iter0, prefix);

if (flags & REF_ITERATOR_SEEK_SET_PREFIX) {
free(iter->prefix);
iter->prefix = xstrdup_or_null(refname);
}
return ref_iterator_seek(iter->iter0, refname, flags);
}

static int prefix_ref_iterator_peel(struct ref_iterator *ref_iterator,

17
refs/packed-backend.c
View File

@ -1004,19 +1004,23 @@ static int packed_ref_iterator_advance(struct ref_iterator *ref_iterator)
}

static int packed_ref_iterator_seek(struct ref_iterator *ref_iterator,
const char *prefix)
const char *refname, unsigned int flags)
{
struct packed_ref_iterator *iter =
(struct packed_ref_iterator *)ref_iterator;
const char *start;

if (prefix && *prefix)
start = find_reference_location(iter->snapshot, prefix, 0);
if (refname && *refname)
start = find_reference_location(iter->snapshot, refname, 0);
else
start = iter->snapshot->start;

free(iter->prefix);
iter->prefix = xstrdup_or_null(prefix);
/* Unset any previously set prefix */
FREE_AND_NULL(iter->prefix);

if (flags & REF_ITERATOR_SEEK_SET_PREFIX)
iter->prefix = xstrdup_or_null(refname);

iter->pos = start;
iter->eof = iter->snapshot->eof;

@ -1194,7 +1198,8 @@ static struct ref_iterator *packed_ref_iterator_begin(
iter->repo = ref_store->repo;
iter->flags = flags;

if (packed_ref_iterator_seek(&iter->base, prefix) < 0) {
if (packed_ref_iterator_seek(&iter->base, prefix,
REF_ITERATOR_SEEK_SET_PREFIX) < 0) {
ref_iterator_free(&iter->base);
return NULL;
}

85
refs/ref-cache.c
View File

@ -434,11 +434,9 @@ static int cache_ref_iterator_advance(struct ref_iterator *ref_iterator)
}
}

static int cache_ref_iterator_seek(struct ref_iterator *ref_iterator,
const char *prefix)
static int cache_ref_iterator_set_prefix(struct cache_ref_iterator *iter,
const char *prefix)
{
struct cache_ref_iterator *iter =
(struct cache_ref_iterator *)ref_iterator;
struct cache_ref_iterator_level *level;
struct ref_dir *dir;

@ -469,6 +467,82 @@ static int cache_ref_iterator_seek(struct ref_iterator *ref_iterator,
return 0;
}

static int cache_ref_iterator_seek(struct ref_iterator *ref_iterator,
const char *refname, unsigned int flags)
{
struct cache_ref_iterator *iter =
(struct cache_ref_iterator *)ref_iterator;

if (flags & REF_ITERATOR_SEEK_SET_PREFIX) {
return cache_ref_iterator_set_prefix(iter, refname);
} else if (refname && *refname) {
struct cache_ref_iterator_level *level;
const char *slash = refname;
struct ref_dir *dir;

dir = get_ref_dir(iter->cache->root);

if (iter->prime_dir)
prime_ref_dir(dir, refname);

iter->levels_nr = 1;
level = &iter->levels[0];
level->index = -1;
level->dir = dir;

/* Unset any previously set prefix */
FREE_AND_NULL(iter->prefix);

/*
* Breakdown the provided seek path and assign the correct
* indexing to each level as needed.
*/
do {
int len, idx;
int cmp = 0;

sort_ref_dir(dir);

slash = strchr(slash, '/');
len = slash ? slash - refname : (int)strlen(refname);

for (idx = 0; idx < dir->nr; idx++) {
cmp = strncmp(refname, dir->entries[idx]->name, len);
if (cmp <= 0)
break;
}
/* don't overflow the index */
idx = idx >= dir->nr ? dir->nr - 1 : idx;

if (slash)
slash = slash + 1;

level->index = idx;
if (dir->entries[idx]->flag & REF_DIR) {
/* push down a level */
dir = get_ref_dir(dir->entries[idx]);

ALLOC_GROW(iter->levels, iter->levels_nr + 1,
iter->levels_alloc);
level = &iter->levels[iter->levels_nr++];
level->dir = dir;
level->index = -1;
} else {
/* reduce the index so the leaf node is iterated over */
if (cmp <= 0 && !slash)
level->index = idx - 1;
/*
* while the seek path may not be exhausted, our
* match is exhausted at a leaf node.
*/
break;
}
} while (slash);
}

return 0;
}

static int cache_ref_iterator_peel(struct ref_iterator *ref_iterator,
struct object_id *peeled)
{
@ -509,7 +583,8 @@ struct ref_iterator *cache_ref_iterator_begin(struct ref_cache *cache,
iter->cache = cache;
iter->prime_dir = prime_dir;

if (cache_ref_iterator_seek(&iter->base, prefix) < 0) {
if (cache_ref_iterator_seek(&iter->base, prefix,
REF_ITERATOR_SEEK_SET_PREFIX) < 0) {
ref_iterator_free(&iter->base);
return NULL;
}

7
refs/refs-internal.h
View File

@ -353,11 +353,12 @@ void base_ref_iterator_init(struct ref_iterator *iter,
typedef int ref_iterator_advance_fn(struct ref_iterator *ref_iterator);

/*
* Seek the iterator to the first reference matching the given prefix. Should
* behave the same as if a new iterator was created with the same prefix.
* Seek the iterator to the first matching reference. If the
* REF_ITERATOR_SEEK_SET_PREFIX flag is set, it would behave the same as if a
* new iterator was created with the provided refname as prefix.
*/
typedef int ref_iterator_seek_fn(struct ref_iterator *ref_iterator,
const char *prefix);
const char *refname, unsigned int flags);

/*
* Peels the current ref, returning 0 for success or -1 for failure.

21
refs/reftable-backend.c
View File

@ -719,15 +719,20 @@ static int reftable_ref_iterator_advance(struct ref_iterator *ref_iterator)
}

static int reftable_ref_iterator_seek(struct ref_iterator *ref_iterator,
const char *prefix)
const char *refname, unsigned int flags)
{
struct reftable_ref_iterator *iter =
(struct reftable_ref_iterator *)ref_iterator;

free(iter->prefix);
iter->prefix = xstrdup_or_null(prefix);
iter->prefix_len = prefix ? strlen(prefix) : 0;
iter->err = reftable_iterator_seek_ref(&iter->iter, prefix);
/* Unset any previously set prefix */
FREE_AND_NULL(iter->prefix);
iter->prefix_len = 0;

if (flags & REF_ITERATOR_SEEK_SET_PREFIX) {
iter->prefix = xstrdup_or_null(refname);
iter->prefix_len = refname ? strlen(refname) : 0;
}
iter->err = reftable_iterator_seek_ref(&iter->iter, refname);

return iter->err;
}
@ -839,7 +844,8 @@ static struct reftable_ref_iterator *ref_iterator_for_stack(struct reftable_ref_
if (ret)
goto done;

ret = reftable_ref_iterator_seek(&iter->base, prefix);
ret = reftable_ref_iterator_seek(&iter->base, prefix,
REF_ITERATOR_SEEK_SET_PREFIX);
if (ret)
goto done;

@ -2042,7 +2048,8 @@ static int reftable_reflog_iterator_advance(struct ref_iterator *ref_iterator)
}

static int reftable_reflog_iterator_seek(struct ref_iterator *ref_iterator UNUSED,
const char *prefix UNUSED)
const char *refname UNUSED,
unsigned int flags UNUSED)
{
BUG("reftable reflog iterator cannot be seeked");
return -1;