Subject: [PATCH] RFC: refs: add GIT_DEBUG_REFS debugging mechanism

From: "Han-Wen Nienhuys via GitGitGadget" <[email-masked]>
Date: Fri, 28 Aug 2020 15:28:49 +0000

From: Han-Wen Nienhuys <[email-masked]>

When set in the environment, GIT_DEBUG_REFS makes git print operations and
results as they flow through the ref storage backend. This helps debug
discrepancies between different ref backends.

This should be integrated with the trace2 sub-system, and I would appreciate
pointers on how to start.

Example:

    $ GIT_DEBUG_REFS=1 ./git branch
    ref_store for .git
    read_raw_ref: HEAD: 0000000000000000000000000000000000000000 (=> refs/heads/ref-debug) type 1: 0
    read_raw_ref: refs/heads/ref-debug: b0728cf8cb9dfd395bea41c646f48108c99230c0 (=> refs/heads/ref-debug) type 0: 0
    ref_iterator_begin: refs/heads/ (0x1)
    iterator_advance before: refs/heads/b4
    iterator_advance before: refs/heads/bla
    ...

Signed-off-by: Han-Wen Nienhuys <[email-masked]>
---
    RFC: refs: add GIT_DEBUG_REFS debugging mechanism
    
    When set in the environment, GIT_DEBUG_REFS makes git print operations
    and results as they flow through the ref storage backend. This helps
    debug discrepancies between different ref backends.
    
    This should be integrated with the trace2 sub-system, and I would
    appreciate pointers on how to start.
    
    Example:
    
    $ GIT_DEBUG_REFS=1 ./git branch
    ref_store for .git
    read_raw_ref: HEAD: 0000000000000000000000000000000000000000 (=> refs/heads/ref-debug) type 1: 0
    read_raw_ref: refs/heads/ref-debug: b0728cf8cb9dfd395bea41c646f48108c99230c0 (=> refs/heads/ref-debug) type 0: 0
    ref_iterator_begin: refs/heads/ (0x1)
    iterator_advance before: refs/heads/b4
    iterator_advance before: refs/heads/bla
    ...
    
    Signed-off-by: Han-Wen Nienhuys [email-masked] [[email-masked]]

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-713%2Fhanwen%2Fdebug-refs-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-713/hanwen/debug-refs-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/713

 Makefile             |   1 +
 refs.c               |   4 +
 refs/debug.c         | 387 +++++++++++++++++++++++++++++++++++++++++++
 refs/refs-internal.h |   6 +
 4 files changed, 398 insertions(+)
 create mode 100644 refs/debug.c

diff --git a/Makefile b/Makefile
index 65f8cfb236..51408fe453 100644
--- a/Makefile
+++ b/Makefile
@@ -957,6 +957,7 @@ LIB_OBJS += rebase.o
 LIB_OBJS += ref-filter.o
 LIB_OBJS += reflog-walk.o
 LIB_OBJS += refs.o
+LIB_OBJS += refs/debug.o
 LIB_OBJS += refs/files-backend.o
 LIB_OBJS += refs/iterator.o
 LIB_OBJS += refs/packed-backend.o
diff --git a/refs.c b/refs.c
index cf91711968..06726f7544 100644
--- a/refs.c
+++ b/refs.c
@@ -1748,6 +1748,10 @@ struct ref_store *get_main_ref_store(struct repository *r)
 		BUG("attempting to get main_ref_store outside of repository");
 
 	r->refs_private = ref_store_init(r->gitdir, REF_STORE_ALL_CAPS);
+	if (getenv("GIT_DEBUG_REFS")) {
+		// XXX - how to hook this up with the trace2 framework?
+		r->refs_private = debug_wrap(r->gitdir, r->refs_private);
+	}
 	return r->refs_private;
 }
 
diff --git a/refs/debug.c b/refs/debug.c
new file mode 100644
index 0000000000..1482c5bd5f
--- /dev/null
+++ b/refs/debug.c
@@ -0,0 +1,387 @@
+
+#include "refs-internal.h"
+
+struct debug_ref_store {
+	struct ref_store base;
+	struct ref_store *refs;
+};
+
+extern struct ref_storage_be refs_be_debug;
+struct ref_store *debug_wrap(const char *gitdir, struct ref_store *store);
+
+struct ref_store *debug_wrap(const char *gitdir, struct ref_store *store)
+{
+	struct debug_ref_store *res = malloc(sizeof(struct debug_ref_store));
+	struct ref_storage_be *be_copy = malloc(sizeof(*be_copy));
+	*be_copy = refs_be_debug;
+	be_copy->name = store->be->name;
+	fprintf(stderr, "ref_store for %s\n", gitdir);
+	res->refs = store;
+	base_ref_store_init((struct ref_store *)res, be_copy);
+	return (struct ref_store *)res;
+}
+
+static int debug_init_db(struct ref_store *refs, struct strbuf *err)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)refs;
+	int res = drefs->refs->be->init_db(drefs->refs, err);
+	fprintf(stderr, "init_db: %d\n", res);
+	return res;
+}
+
+static int debug_transaction_prepare(struct ref_store *refs,
+				     struct ref_transaction *transaction,
+				     struct strbuf *err)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)refs;
+	int res;
+	transaction->ref_store = drefs->refs;
+	res = drefs->refs->be->transaction_prepare(drefs->refs, transaction,
+						   err);
+	fprintf(stderr, "transaction_prepare: %d\n", res);
+	return res;
+}
+
+static void print_update(int i, const char *refname,
+			 const struct object_id *old_oid,
+			 const struct object_id *new_oid, unsigned int flags,
+			 unsigned int type, const char *msg)
+{
+	char o[200] = "null";
+	char n[200] = "null";
+	if (old_oid)
+		oid_to_hex_r(o, old_oid);
+	if (new_oid)
+		oid_to_hex_r(n, new_oid);
+
+	type &= 0xf; /* see refs.h REF_* */
+	flags &= REF_HAVE_NEW | REF_HAVE_OLD | REF_NO_DEREF |
+		REF_FORCE_CREATE_REFLOG; // XXX: LOG_ONLY
+	fprintf(stderr, "%d: %s %s -> %s (F=0x%x, T=0x%x) \"%s\"\n", i, refname,
+		o, n, flags, type, msg);
+}
+
+static void print_transaction(struct ref_transaction *transaction)
+{
+	fprintf(stderr, "transaction {\n");
+	for (int i = 0; i < transaction->nr; i++) {
+		struct ref_update *u = transaction->updates[i];
+		print_update(i, u->refname, &u->old_oid, &u->new_oid, u->flags,
+			     u->type, u->msg);
+	}
+	fprintf(stderr, "}\n");
+}
+
+static int debug_transaction_finish(struct ref_store *refs,
+				    struct ref_transaction *transaction,
+				    struct strbuf *err)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)refs;
+	int res;
+	transaction->ref_store = drefs->refs;
+	res = drefs->refs->be->transaction_finish(drefs->refs, transaction,
+						  err);
+	print_transaction(transaction);
+	fprintf(stderr, "finish: %d\n", res);
+	return res;
+}
+
+static int debug_transaction_abort(struct ref_store *refs,
+				   struct ref_transaction *transaction,
+				   struct strbuf *err)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)refs;
+	int res;
+	transaction->ref_store = drefs->refs;
+	res = drefs->refs->be->transaction_abort(drefs->refs, transaction, err);
+	return res;
+}
+
+static int debug_initial_transaction_commit(struct ref_store *refs,
+					    struct ref_transaction *transaction,
+					    struct strbuf *err)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)refs;
+	int res;
+	transaction->ref_store = drefs->refs;
+	res = drefs->refs->be->initial_transaction_commit(drefs->refs,
+							  transaction, err);
+	return res;
+}
+
+static int debug_pack_refs(struct ref_store *ref_store, unsigned int flags)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	int res = drefs->refs->be->pack_refs(drefs->refs, flags);
+	fprintf(stderr, "pack_refs: %d\n", res);
+	return res;
+}
+
+static int debug_create_symref(struct ref_store *ref_store,
+			       const char *ref_name, const char *target,
+			       const char *logmsg)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	int res = drefs->refs->be->create_symref(drefs->refs, ref_name, target,
+						 logmsg);
+	fprintf(stderr, "create_symref: %s -> %s \"%s\": %d\n", ref_name,
+		target, logmsg, res);
+	return res;
+}
+
+static int debug_delete_refs(struct ref_store *ref_store, const char *msg,
+			     struct string_list *refnames, unsigned int flags)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	int res =
+		drefs->refs->be->delete_refs(drefs->refs, msg, refnames, flags);
+	int i = 0;
+	fprintf(stderr, "delete_refs {\n");
+	for (i = 0; i < refnames->nr; i++)
+		fprintf(stderr, "%s\n", refnames->items[i].string);
+	fprintf(stderr, "}: %d\n", res);
+	return res;
+}
+
+static int debug_rename_ref(struct ref_store *ref_store, const char *oldref,
+			    const char *newref, const char *logmsg)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	int res = drefs->refs->be->rename_ref(drefs->refs, oldref, newref,
+					      logmsg);
+	fprintf(stderr, "rename_ref: %s -> %s \"%s\": %d\n", oldref, newref,
+		logmsg, res);
+	return res;
+}
+
+static int debug_copy_ref(struct ref_store *ref_store, const char *oldref,
+			  const char *newref, const char *logmsg)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	int res =
+		drefs->refs->be->copy_ref(drefs->refs, oldref, newref, logmsg);
+	fprintf(stderr, "copy_ref: %s -> %s \"%s\": %d\n", oldref, newref,
+		logmsg, res);
+	return res;
+}
+
+struct debug_ref_iterator {
+	struct ref_iterator base;
+	struct ref_iterator *iter;
+};
+
+static int debug_ref_iterator_advance(struct ref_iterator *ref_iterator)
+{
+	struct debug_ref_iterator *diter =
+		(struct debug_ref_iterator *)ref_iterator;
+	int res = diter->iter->vtable->advance(diter->iter);
+	if (res)
+		fprintf(stderr, "iterator_advance: %d\n", res);
+	else
+		fprintf(stderr, "iterator_advance before: %s\n",
+			diter->iter->refname);
+
+	diter->base.ordered = diter->iter->ordered;
+	diter->base.refname = diter->iter->refname;
+	diter->base.oid = diter->iter->oid;
+	diter->base.flags = diter->iter->flags;
+	return res;
+}
+static int debug_ref_iterator_peel(struct ref_iterator *ref_iterator,
+				   struct object_id *peeled)
+{
+	struct debug_ref_iterator *diter =
+		(struct debug_ref_iterator *)ref_iterator;
+	int res = diter->iter->vtable->peel(diter->iter, peeled);
+	fprintf(stderr, "iterator_peel: %s: %d\n", diter->iter->refname, res);
+	return res;
+}
+
+static int debug_ref_iterator_abort(struct ref_iterator *ref_iterator)
+{
+	struct debug_ref_iterator *diter =
+		(struct debug_ref_iterator *)ref_iterator;
+	int res = diter->iter->vtable->abort(diter->iter);
+	fprintf(stderr, "iterator_abort: %d\n", res);
+	return res;
+}
+
+static struct ref_iterator_vtable debug_ref_iterator_vtable = {
+	debug_ref_iterator_advance, debug_ref_iterator_peel,
+	debug_ref_iterator_abort
+};
+
+static struct ref_iterator *
+debug_ref_iterator_begin(struct ref_store *ref_store, const char *prefix,
+			 unsigned int flags)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	struct ref_iterator *res =
+		drefs->refs->be->iterator_begin(drefs->refs, prefix, flags);
+	struct debug_ref_iterator *diter = xcalloc(1, sizeof(*diter));
+	base_ref_iterator_init(&diter->base, &debug_ref_iterator_vtable, 1);
+	diter->iter = res;
+	fprintf(stderr, "ref_iterator_begin: %s (0x%x)\n", prefix, flags);
+	return &diter->base;
+}
+
+static int debug_read_raw_ref(struct ref_store *ref_store, const char *refname,
+			      struct object_id *oid, struct strbuf *referent,
+			      unsigned int *type)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	int res = 0;
+
+	oidcpy(oid, &null_oid);
+	res = drefs->refs->be->read_raw_ref(drefs->refs, refname, oid, referent,
+					    type);
+
+	if (res == 0) {
+		fprintf(stderr, "read_raw_ref: %s: %s (=> %s) type %x: %d\n",
+			refname, oid_to_hex(oid), referent->buf, *type, res);
+	} else {
+		fprintf(stderr, "read_raw_ref: %s err %d\n", refname, res);
+	}
+	return res;
+}
+
+static struct ref_iterator *
+debug_reflog_iterator_begin(struct ref_store *ref_store)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	struct ref_iterator *res =
+		drefs->refs->be->reflog_iterator_begin(drefs->refs);
+	fprintf(stderr, "for_each_reflog_iterator_begin\n");
+	return res;
+}
+
+struct debug_reflog {
+	const char *refname;
+	each_reflog_ent_fn *fn;
+	void *cb_data;
+};
+
+static int debug_print_reflog_ent(struct object_id *old_oid,
+				  struct object_id *new_oid,
+				  const char *committer, timestamp_t timestamp,
+				  int tz, const char *msg, void *cb_data)
+{
+	struct debug_reflog *dbg = (struct debug_reflog *)cb_data;
+	int ret;
+	char o[100] = "null";
+	char n[100] = "null";
+	if (old_oid)
+		oid_to_hex_r(o, old_oid);
+	if (new_oid)
+		oid_to_hex_r(n, new_oid);
+
+	ret = dbg->fn(old_oid, new_oid, committer, timestamp, tz, msg,
+		      dbg->cb_data);
+	fprintf(stderr, "reflog_ent %s (ret %d): %s -> %s, %s %ld \"%s\"\n",
+		dbg->refname, ret, o, n, committer, (long int)timestamp, msg);
+	return ret;
+}
+
+static int debug_for_each_reflog_ent(struct ref_store *ref_store,
+				     const char *refname, each_reflog_ent_fn fn,
+				     void *cb_data)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	struct debug_reflog dbg = {
+		.refname = refname,
+		.fn = fn,
+		.cb_data = cb_data,
+	};
+
+	int res = drefs->refs->be->for_each_reflog_ent(
+		drefs->refs, refname, &debug_print_reflog_ent, &dbg);
+	fprintf(stderr, "for_each_reflog: %s: %d\n", refname, res);
+	return res;
+}
+
+static int debug_for_each_reflog_ent_reverse(struct ref_store *ref_store,
+					     const char *refname,
+					     each_reflog_ent_fn fn,
+					     void *cb_data)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	struct debug_reflog dbg = {
+		.refname = refname,
+		.fn = fn,
+		.cb_data = cb_data,
+	};
+	int res = drefs->refs->be->for_each_reflog_ent_reverse(
+		drefs->refs, refname, &debug_print_reflog_ent, &dbg);
+	fprintf(stderr, "for_each_reflog_reverse: %s: %d\n", refname, res);
+	return res;
+}
+
+static int debug_reflog_exists(struct ref_store *ref_store, const char *refname)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	int res = drefs->refs->be->reflog_exists(drefs->refs, refname);
+	fprintf(stderr, "reflog_exists: %s: %d\n", refname, res);
+	return res;
+}
+
+static int debug_create_reflog(struct ref_store *ref_store, const char *refname,
+			       int force_create, struct strbuf *err)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	int res = drefs->refs->be->create_reflog(drefs->refs, refname,
+						 force_create, err);
+	fprintf(stderr, "create_reflog: %s: %d\n", refname, res);
+	return res;
+}
+
+static int debug_delete_reflog(struct ref_store *ref_store, const char *refname)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	int res = drefs->refs->be->delete_reflog(drefs->refs, refname);
+	fprintf(stderr, "delete_reflog: %s: %d\n", refname, res);
+	return res;
+}
+
+static int debug_reflog_expire(struct ref_store *ref_store, const char *refname,
+			       const struct object_id *oid, unsigned int flags,
+			       reflog_expiry_prepare_fn prepare_fn,
+			       reflog_expiry_should_prune_fn should_prune_fn,
+			       reflog_expiry_cleanup_fn cleanup_fn,
+			       void *policy_cb_data)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	int res = drefs->refs->be->reflog_expire(drefs->refs, refname, oid,
+						 flags, prepare_fn,
+						 should_prune_fn, cleanup_fn,
+						 policy_cb_data);
+	fprintf(stderr, "reflog_expire: %s: %d\n", refname, res);
+	return res;
+}
+
+struct ref_storage_be refs_be_debug = {
+	NULL,
+	"debug",
+	NULL,
+	debug_init_db,
+	debug_transaction_prepare,
+	debug_transaction_finish,
+	debug_transaction_abort,
+	debug_initial_transaction_commit,
+
+	debug_pack_refs,
+	debug_create_symref,
+	debug_delete_refs,
+	debug_rename_ref,
+	debug_copy_ref,
+
+	debug_ref_iterator_begin,
+	debug_read_raw_ref,
+
+	debug_reflog_iterator_begin,
+	debug_for_each_reflog_ent,
+	debug_for_each_reflog_ent_reverse,
+	debug_reflog_exists,
+	debug_create_reflog,
+	debug_delete_reflog,
+	debug_reflog_expire,
+};
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 357359a0be..ec28ae5d86 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -681,4 +681,10 @@ struct ref_store {
 void base_ref_store_init(struct ref_store *refs,
 			 const struct ref_storage_be *be);
 
+/*
+ * Print out ref operations as they occur. Useful for debugging alternate ref
+ * backends.
+ */
+struct ref_store *debug_wrap(const char *gitdir, struct ref_store *store);
+
 #endif /* REFS_REFS_INTERNAL_H */

base-commit: 675a4aaf3b226c0089108221b96559e0baae5de9
-- 
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