[PATCH 5/7] tmp-objdir: new API for creating and removing primary object dirs

From: Elijah Newren via GitGitGadget <gitgitgadget@gmail.com>
Date: Aug 31, 2021, 02:26 UTC
Message-ID: <67d3b2b09f9ddda616cdd0d1b12ab7afc73670ed.1630376800.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.1080.git.git.1630376800.gitgitgadget@gmail.com>

From: Elijah Newren <newren@gmail.com>

The tmp_objdir API provides the ability to create temporary object directories, but was designed with the goal of having subprocesses access these object stores, followed by the main process migrating objects from it to the main object store or just deleting it. The subprocesses would view it as their primary datastore and write to it.

For the --remerge-diff option we want to add to show & log, we want all writes of intermediate merge results (both blobs and trees) to go to this alternate object store; since those writes will be done by the main process, we need this "alternate" object store to actually be the primary object store. When show & log are done, they'll simply remove this temporary object store.

We also need one more thing -- `git log --remerge-diff` can cause the temporary object store to fill up with loose objects. Rather than trying to gc that are known garbage anyway, we simply want to know the location of the temporary object store so we can purge the loose objects after each merge.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 tmp-objdir.c | 29 +++++++++++++++++++++++++++++
 tmp-objdir.h | 16 ++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/tmp-objdir.c b/tmp-objdir.c
index b8d880e3626..9f75a75d1c0 100644
--- a/tmp-objdir.c
+++ b/tmp-objdir.c
@@ -288,7 +288,36 @@ const char **tmp_objdir_env(const struct tmp_objdir *t)
 	return t->env.v;
 }
 
+const char *tmp_objdir_path(struct tmp_objdir *t)
+{
+	return t->path.buf;
+}
+
 void tmp_objdir_add_as_alternate(const struct tmp_objdir *t)
 {
 	add_to_alternates_memory(t->path.buf);
 }
+
+void tmp_objdir_make_primary(struct repository *r, const struct tmp_objdir *t)
+{
+	struct object_directory *od;
+	od = xcalloc(1, sizeof(*od));
+
+	od->path = xstrdup(t->path.buf);
+	od->next = r->objects->odb;
+	r->objects->odb = od;
+}
+
+void tmp_objdir_remove_as_primary(struct repository *r,
+				  const struct tmp_objdir *t)
+{
+	struct object_directory *od;
+
+	od = r->objects->odb;
+	if (strcmp(t->path.buf, od->path))
+		BUG("expected %s as primary object store; found %s",
+		    t->path.buf, od->path);
+	r->objects->odb = od->next;
+	free(od->path);
+	free(od);
+}
diff --git a/tmp-objdir.h b/tmp-objdir.h
index b1e45b4c75d..6067da24e8c 100644
--- a/tmp-objdir.h
+++ b/tmp-objdir.h
@@ -19,6 +19,7 @@
  *
  */
 
+struct repository;
 struct tmp_objdir;
 
 /*
@@ -33,6 +34,11 @@ struct tmp_objdir *tmp_objdir_create(void);
  */
 const char **tmp_objdir_env(const struct tmp_objdir *);
 
+/*
+ * Return the path used for the temporary object directory.
+ */
+const char *tmp_objdir_path(struct tmp_objdir *t);
+
 /*
  * Finalize a temporary object directory by migrating its objects into the main
  * object database, removing the temporary directory, and freeing any
@@ -51,4 +57,14 @@ int tmp_objdir_destroy(struct tmp_objdir *);
  */
 void tmp_objdir_add_as_alternate(const struct tmp_objdir *);
 
+/*
+ * Add the temporary object directory as the *primary* object store in the
+ * current process, turning the previous primary object store into an
+ * alternate.
+ */
+void tmp_objdir_make_primary(struct repository *r,
+			     const struct tmp_objdir *t);
+void tmp_objdir_remove_as_primary(struct repository *r,
+				  const struct tmp_objdir *t);
+
 #endif /* TMP_OBJDIR_H */

-- 
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