[GSoC][PATCH v9 4/9] refs: set up ref consistency check infrastructure

[shejialuo <shejialuo@gmail.com>]

The interfaces defined in the `ref_storage_be` are carefully structured
in semantic. It's organized as the five parts:

1. The name and the initialization interfaces.
2. The ref transaction interfaces.
3. The ref internal interfaces (pack, rename and copy).
4. The ref filesystem interfaces.
5. The reflog related interfaces.

To keep consistent with the git-fsck(1), add a new interface named
"fsck_refs_fn" to the end of "ref_storage_be". This semantic cannot be
grouped into any above five categories. Explicitly add blank line to
make it different from others.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
---
 refs.c                  |  5 +++++
 refs.h                  |  8 ++++++++
 refs/debug.c            | 11 +++++++++++
 refs/files-backend.c    | 15 ++++++++++++++-
 refs/packed-backend.c   |  8 ++++++++
 refs/refs-internal.h    |  6 ++++++
 refs/reftable-backend.c |  8 ++++++++
 7 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/refs.c b/refs.c
index bb90a18875..410919246b 100644
--- a/refs.c
+++ b/refs.c
@@ -318,6 +318,11 @@ int check_refname_format(const char *refname, int flags)
 	return check_or_sanitize_refname(refname, flags, NULL);
 }
 
+int refs_fsck(struct ref_store *refs, struct fsck_options *o)
+{
+	return refs->be->fsck(refs, o);
+}
+
 void sanitize_refname_component(const char *refname, struct strbuf *out)
 {
 	if (check_or_sanitize_refname(refname, REFNAME_ALLOW_ONELEVEL, out))
diff --git a/refs.h b/refs.h
index 0ecba21b4a..804d6a7fce 100644
--- a/refs.h
+++ b/refs.h
@@ -4,6 +4,7 @@
 #include "commit.h"
 #include "repository.h"
 
+struct fsck_options;
 struct object_id;
 struct ref_store;
 struct strbuf;
@@ -541,6 +542,13 @@ int refs_for_each_reflog(struct ref_store *refs, each_reflog_fn fn, void *cb_dat
  */
 int check_refname_format(const char *refname, int flags);
 
+/*
+ * Check the reference database for consistency. Return 0 if refs and
+ * reflogs are consistent, and non-zero otherwise. The errors will be
+ * written to stderr.
+ */
+int refs_fsck(struct ref_store *refs, struct fsck_options *o);
+
 /*
  * Apply the rules from check_refname_format, but mutate the result until it
  * is acceptable, and place the result in "out".
diff --git a/refs/debug.c b/refs/debug.c
index 547d9245b9..45e2e784a0 100644
--- a/refs/debug.c
+++ b/refs/debug.c
@@ -419,6 +419,15 @@ static int debug_reflog_expire(struct ref_store *ref_store, const char *refname,
 	return res;
 }
 
+static int debug_fsck(struct ref_store *ref_store,
+		      struct fsck_options *o)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	int res = drefs->refs->be->fsck(drefs->refs, o);
+	trace_printf_key(&trace_refs, "fsck: %d\n", res);
+	return res;
+}
+
 struct ref_storage_be refs_be_debug = {
 	.name = "debug",
 	.init = NULL,
@@ -451,4 +460,6 @@ struct ref_storage_be refs_be_debug = {
 	.create_reflog = debug_create_reflog,
 	.delete_reflog = debug_delete_reflog,
 	.reflog_expire = debug_reflog_expire,
+
+	.fsck = debug_fsck,
 };
diff --git a/refs/files-backend.c b/refs/files-backend.c
index aa52d9be7c..d89eeda8ef 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -3408,6 +3408,17 @@ static int files_ref_store_remove_on_disk(struct ref_store *ref_store,
 	return ret;
 }
 
+static int files_fsck(struct ref_store *ref_store,
+		      struct fsck_options *o)
+{
+	int ret;
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_READ, "fsck");
+
+	ret = refs->packed_ref_store->be->fsck(refs->packed_ref_store, o);
+	return ret;
+}
+
 struct ref_storage_be refs_be_files = {
 	.name = "files",
 	.init = files_ref_store_init,
@@ -3434,5 +3445,7 @@ struct ref_storage_be refs_be_files = {
 	.reflog_exists = files_reflog_exists,
 	.create_reflog = files_create_reflog,
 	.delete_reflog = files_delete_reflog,
-	.reflog_expire = files_reflog_expire
+	.reflog_expire = files_reflog_expire,
+
+	.fsck = files_fsck,
 };
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index a0666407cd..5209b0b212 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -1735,6 +1735,12 @@ static struct ref_iterator *packed_reflog_iterator_begin(struct ref_store *ref_s
 	return empty_ref_iterator_begin();
 }
 
+static int packed_fsck(struct ref_store *ref_store,
+		       struct fsck_options *o)
+{
+	return 0;
+}
+
 struct ref_storage_be refs_be_packed = {
 	.name = "packed",
 	.init = packed_ref_store_init,
@@ -1762,4 +1768,6 @@ struct ref_storage_be refs_be_packed = {
 	.create_reflog = NULL,
 	.delete_reflog = NULL,
 	.reflog_expire = NULL,
+
+	.fsck = packed_fsck,
 };
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index fa975d69aa..a905e187cd 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -4,6 +4,7 @@
 #include "refs.h"
 #include "iterator.h"
 
+struct fsck_options;
 struct ref_transaction;
 
 /*
@@ -650,6 +651,9 @@ typedef int read_raw_ref_fn(struct ref_store *ref_store, const char *refname,
 typedef int read_symbolic_ref_fn(struct ref_store *ref_store, const char *refname,
 				 struct strbuf *referent);
 
+typedef int fsck_fn(struct ref_store *ref_store,
+		    struct fsck_options *o);
+
 struct ref_storage_be {
 	const char *name;
 	ref_store_init_fn *init;
@@ -677,6 +681,8 @@ struct ref_storage_be {
 	create_reflog_fn *create_reflog;
 	delete_reflog_fn *delete_reflog;
 	reflog_expire_fn *reflog_expire;
+
+	fsck_fn *fsck;
 };
 
 extern struct ref_storage_be refs_be_files;
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index fbe74c239d..b5a1a526df 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -2303,6 +2303,12 @@ static int reftable_be_reflog_expire(struct ref_store *ref_store,
 	return ret;
 }
 
+static int reftable_be_fsck(struct ref_store *ref_store,
+			    struct fsck_options *o)
+{
+	return 0;
+}
+
 struct ref_storage_be refs_be_reftable = {
 	.name = "reftable",
 	.init = reftable_be_init,
@@ -2330,4 +2336,6 @@ struct ref_storage_be refs_be_reftable = {
 	.create_reflog = reftable_be_create_reflog,
 	.delete_reflog = reftable_be_delete_reflog,
 	.reflog_expire = reftable_be_reflog_expire,
+
+	.fsck = reftable_be_fsck,
 };
-- 
2.45.2