Re: [PATCH v2 2/2] shallow.c: use '{commit,rollback}_shallow_file'
From: Taylor Blau <hidden>
Date: 2020-06-03 22:14:57
Possibly related (same subject, not in this thread)
- 2020-04-24 · Re: [PATCH v2 2/2] shallow.c: use '{commit,rollback}_shallow_file' · Taylor Blau <hidden>
- 2020-04-23 · Re: [PATCH v2 2/2] shallow.c: use '{commit,rollback}_shallow_file' · Junio C Hamano <hidden>
On Wed, Jun 03, 2020 at 01:51:51PM -0700, Jonathan Nieder wrote:
Taylor Blau wrote:quoted
Ah, this only sort of has to do with the object cache. In 'parse_commit_buffer()' we stop parsing parents in the case that the repository is shallow (this goes back to 7f3140cd23 (git repack: keep commits hidden by a graft, 2009-07-23)).Ah, good analysis. (In fact, the behavior is older: it's from 5da5c8f4cf4 (Teach parse_commit_buffer about grafting., 2005-07-30).) So this is additional "cached" data that needs to be invalidated by reset_repository_shallow. So the question is, what other information falls into that category? [...]quoted
--- a/shallow.c +++ b/shallow.c@@ -90,6 +90,9 @@ static void reset_repository_shallow(struct repository *r) { r->parsed_objects->is_shallow = -1; stat_validity_clear(r->parsed_objects->shallow_stat); +(nit: the above two lines wouldn't be needed if r->parsed_objects is being thrown away.)
Right, thanks. I don't think that it matters since you point out a legitimate issue with dangling references, but serves me right for working on this so late at night ;-).
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+ parsed_object_pool_clear(r->parsed_objects); + r->parsed_objects = parsed_object_pool_new(); }Shallows don't affect the ref store. They only affect object walks. So r->parsed_objects does seem like the only place that could be affected. That said, with this change I'd worry about use-after-free from any existing references to objects in the pool. Stepping back, what I think I would like to see is to *not* have grafts and shallow state affect the in-memory persisted parsed objects. Instead, act as an overlay in accessors that traverse over them. Lacking that, I like the idea of a "dirty bit" that gets written as soon as we have started lying in the parsed object pool. Something like this. What do you think?diff --git i/commit-graph.c w/commit-graph.c index 2ff042fbf4f..84b49ce903b 100644 --- i/commit-graph.c +++ w/commit-graph.c@@ -149,7 +149,8 @@ static int commit_graph_compatible(struct repository *r) } prepare_commit_graft(r); - if (r->parsed_objects && r->parsed_objects->grafts_nr) + if (r->parsed_objects && + (r->parsed_objects->grafts_nr || r->parsed_objects->substituted_parent))
This is a little tricky. Why would we set substituted_parent without also incrementing grafts_nr? That seems like the real bug here: if we incremented grafts_nr, then we would return a non-zero value from 'commit_graph_compatible' and rightly stop even without this sticky-bit. I don't quite understand this myself. If it's an oversight, it's a remarkably long-lived one. Do you have a better sense of this?
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return 0; if (is_repository_shallow(r)) return 0;diff --git i/commit.c w/commit.c index 87686a7055b..762f09e53ae 100644 --- i/commit.c +++ w/commit.c@@ -423,6 +423,8 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b pptr = &item->parents; graft = lookup_commit_graft(r, &item->object.oid); + if (graft) + r->parsed_objects->substituted_parent = 1; while (bufptr + parent_entry_len < tail && !memcmp(bufptr, "parent ", 7)) { struct commit *new_parent;@@ -447,6 +449,7 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b if (graft) { int i; struct commit *new_parent; +
Nit: unnecessary whitespace change, but I doubt it really matters much.
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for (i = 0; i < graft->nr_parent; i++) { new_parent = lookup_commit(r, &graft->parent[i]);diff --git i/object.h w/object.h index b22328b8383..db02fdcd6b2 100644 --- i/object.h +++ w/object.h@@ -26,6 +26,7 @@ struct parsed_object_pool { char *alternate_shallow_file; int commit_graft_prepared; + int substituted_parent; struct buffer_slab *buffer_slab; };Thanks, Jonathan
Thanks, Taylor