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From: Jonathan Tan <jonathantanmy@google.com>
To: git@vger.kernel.org
Cc: Jonathan Tan <jonathantanmy@google.com>,
	stolee@gmail.com, gitster@pobox.com
Subject: [PATCH v3 4/7] fetch: only populate existing_refs if needed
Date: Mon, 17 Aug 2020 21:01:34 -0700	[thread overview]
Message-ID: <a5554cd27f8aac5018e5699837e3b9e9badcd3a4.1597722942.git.jonathantanmy@google.com> (raw)
In-Reply-To: <cover.1597722941.git.jonathantanmy@google.com>

In "fetch", get_ref_map() iterates over all refs to populate
"existing_refs" in order to populate peer_ref->old_oid in the returned
refmap, even if the refmap has no peer_ref set - which is the case when
only literal hashes (i.e. no refs by name) are fetched.

Iterating over refs causes the targets of those refs to be checked for
existence. Avoiding this is especially important when we use "git fetch"
to perform lazy fetches in a partial clone because a target of such a
ref may need to be itself lazy-fetched (and otherwise causing an
infinite loop).

Therefore, avoid populating "existing_refs" until necessary. With this
patch, because Git lazy-fetches objects by literal hashes (to be done in
a subsequent commit), it will then be able to guarantee avoiding reading
targets of refs.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
---
 builtin/fetch.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index 29db219c68..6460ce3f4e 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -449,6 +449,7 @@ static struct ref *get_ref_map(struct remote *remote,
 	struct ref *orefs = NULL, **oref_tail = &orefs;
 
 	struct hashmap existing_refs;
+	int existing_refs_populated = 0;
 
 	if (rs->nr) {
 		struct refspec *fetch_refspec;
@@ -542,15 +543,18 @@ static struct ref *get_ref_map(struct remote *remote,
 
 	ref_map = ref_remove_duplicates(ref_map);
 
-	refname_hash_init(&existing_refs);
-	for_each_ref(add_one_refname, &existing_refs);
-
 	for (rm = ref_map; rm; rm = rm->next) {
 		if (rm->peer_ref) {
 			const char *refname = rm->peer_ref->name;
 			struct refname_hash_entry *peer_item;
 			unsigned int hash = strhash(refname);
 
+			if (!existing_refs_populated) {
+				refname_hash_init(&existing_refs);
+				for_each_ref(add_one_refname, &existing_refs);
+				existing_refs_populated = 1;
+			}
+
 			peer_item = hashmap_get_entry_from_hash(&existing_refs,
 						hash, refname,
 						struct refname_hash_entry, ent);
@@ -560,7 +564,8 @@ static struct ref *get_ref_map(struct remote *remote,
 			}
 		}
 	}
-	hashmap_free_entries(&existing_refs, struct refname_hash_entry, ent);
+	if (existing_refs_populated)
+		hashmap_free_entries(&existing_refs, struct refname_hash_entry, ent);
 
 	return ref_map;
 }
-- 
2.28.0.220.ged08abb693-goog


  parent reply	other threads:[~2020-08-18  4:02 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-24 22:38 [RFC PATCH] Modify fetch-pack to no longer die on error? Jonathan Tan
2020-07-24 23:07 ` Junio C Hamano
2020-07-24 23:11 ` Junio C Hamano
2020-07-25 21:41   ` Jeff King
2020-07-25 23:01     ` Junio C Hamano
2020-07-27 17:11       ` Jeff King
2020-07-28 19:23       ` Jonathan Tan
2020-07-28 20:08         ` Jeff King
2020-07-29 18:53           ` Jonathan Tan
2020-07-29 19:29             ` Jeff King
2020-07-29 19:02           ` Junio C Hamano
2020-07-29 22:55             ` Jonathan Tan
2020-08-05  1:20 ` [RFC PATCH 0/7] Lazy fetch with subprocess Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 1/7] fetch-pack: allow NULL negotiator->add_tip Jonathan Tan
2020-08-05 19:53     ` Junio C Hamano
2020-08-07 20:53       ` Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 2/7] fetch-pack: allow NULL negotiator->known_common Jonathan Tan
2020-08-05 20:08     ` Junio C Hamano
2020-08-05 22:11       ` Junio C Hamano
2020-08-07 20:59         ` Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 3/7] negotiator/null: add null fetch negotiator Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 4/7] fetch: --stdin Jonathan Tan
2020-08-05 20:33     ` Junio C Hamano
2020-08-07 21:10       ` Jonathan Tan
2020-08-07 21:58         ` Junio C Hamano
2020-08-07 21:10       ` Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 5/7] fetch: submodule config Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 6/7] fetch: only populate existing_refs if needed Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 7/7] promisor-remote: use subprocess to fetch Jonathan Tan
2020-08-11 22:52 ` [PATCH v2 0/7] Lazy fetch with subprocess Jonathan Tan
2020-08-11 22:52   ` [PATCH v2 1/7] negotiator/null: add null fetch negotiator Jonathan Tan
2020-08-12 12:55     ` Derrick Stolee
2020-08-12 16:44       ` Junio C Hamano
2020-08-12 17:29         ` Jonathan Tan
2020-08-11 22:52   ` [PATCH v2 2/7] fetch: allow refspecs specified through stdin Jonathan Tan
2020-08-11 22:52   ` [PATCH v2 3/7] fetch: avoid reading submodule config until needed Jonathan Tan
2020-08-12 17:34     ` Junio C Hamano
2020-08-11 22:52   ` [PATCH v2 4/7] fetch: only populate existing_refs if needed Jonathan Tan
2020-08-12 18:06     ` Junio C Hamano
2020-08-11 22:52   ` [PATCH v2 5/7] fetch-pack: do not lazy-fetch during ref iteration Jonathan Tan
2020-08-12 18:25     ` Junio C Hamano
2020-08-11 22:52   ` [PATCH v2 6/7] promisor-remote: lazy-fetch objects in subprocess Jonathan Tan
2020-08-12 18:28     ` Junio C Hamano
2020-08-11 22:52   ` [PATCH v2 7/7] fetch-pack: remove no_dependents code Jonathan Tan
2020-08-12 12:51   ` [PATCH v2 0/7] Lazy fetch with subprocess Derrick Stolee
2020-08-18  4:01 ` [PATCH v3 " Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 1/7] negotiator/noop: add noop fetch negotiator Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 2/7] fetch: allow refspecs specified through stdin Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 3/7] fetch: avoid reading submodule config until needed Jonathan Tan
2020-08-18  4:01   ` Jonathan Tan [this message]
2020-08-18  4:01   ` [PATCH v3 5/7] fetch-pack: do not lazy-fetch during ref iteration Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 6/7] promisor-remote: lazy-fetch objects in subprocess Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 7/7] fetch-pack: remove no_dependents code Jonathan Tan
2020-08-18 19:56   ` [PATCH v3 0/7] Lazy fetch with subprocess Junio C Hamano
2020-08-18 22:32     ` Junio C Hamano
2020-08-18 23:36       ` [PATCH] fixup! promisor-remote: lazy-fetch objects in subprocess Jonathan Tan
2020-08-18 23:57         ` Junio C Hamano

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