[PATCH 1/6] refs.c: add an err argument to log_ref_setup

[David Turner <dturner@twopensource.com>]

Add err argument to log_ref_setup that can explain the reason for a
failure. This then eliminates the need to manage errno through this
function since we can just add strerror(errno) to the err string when
meaningful. No callers relied on errno from this function for anything
else than the error message.

write_ref_to_lockfile is a private function that calls
log_ref_setup. Update this function to also take an err argument and
fill it in.  This again eliminates the need to manage errno in this
function.

Update of a patch by Ronnie Sahlberg.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Signed-off-by: David Turner <dturner@twitter.com>
---
 builtin/checkout.c |   8 ++--
 refs.c             | 111 ++++++++++++++++++++++++++++-------------------------
 refs.h             |   4 +-
 3 files changed, 66 insertions(+), 57 deletions(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index c018ab3..ac4d10a 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -624,16 +624,18 @@ static void update_refs_for_switch(const struct checkout_opts *opts,
 				struct strbuf log_file = STRBUF_INIT;
 				int ret;
 				const char *ref_name;
+				struct strbuf err = STRBUF_INIT;
 
 				ref_name = mkpath("refs/heads/%s", opts->new_orphan_branch);
 				temp = log_all_ref_updates;
 				log_all_ref_updates = 1;
-				ret = log_ref_setup(ref_name, &log_file);
+				ret = log_ref_setup(ref_name, &log_file, &err);
 				log_all_ref_updates = temp;
 				strbuf_release(&log_file);
 				if (ret) {
-					fprintf(stderr, _("Can not do reflog for '%s'\n"),
-					    opts->new_orphan_branch);
+					fprintf(stderr, _("Can not do reflog for '%s'. %s\n"),
+					opts->new_orphan_branch, err.buf);
+					strbuf_release(&err);
 					return;
 				}
 			}
diff --git a/refs.c b/refs.c
index fb568d7..b34a54a 100644
--- a/refs.c
+++ b/refs.c
@@ -2975,9 +2975,11 @@ static int rename_ref_available(const char *oldname, const char *newname)
 	return ret;
 }
 
-static int write_ref_to_lockfile(struct ref_lock *lock, const unsigned char *sha1);
+static int write_ref_to_lockfile(struct ref_lock *lock,
+				 const unsigned char *sha1, struct strbuf* err);
 static int commit_ref_update(struct ref_lock *lock,
-			     const unsigned char *sha1, const char *logmsg);
+			     const unsigned char *sha1, const char *logmsg,
+			     struct strbuf *err);
 
 int rename_ref(const char *oldrefname, const char *newrefname, const char *logmsg)
 {
@@ -3038,9 +3040,10 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
 	}
 	hashcpy(lock->old_oid.hash, orig_sha1);
 
-	if (write_ref_to_lockfile(lock, orig_sha1) ||
-	    commit_ref_update(lock, orig_sha1, logmsg)) {
-		error("unable to write current sha1 into %s", newrefname);
+	if (write_ref_to_lockfile(lock, orig_sha1, &err) ||
+	    commit_ref_update(lock, orig_sha1, logmsg, &err)) {
+		error("unable to write current sha1 into %s: %s", newrefname, err.buf);
+		strbuf_release(&err);
 		goto rollback;
 	}
 
@@ -3056,9 +3059,11 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
 
 	flag = log_all_ref_updates;
 	log_all_ref_updates = 0;
-	if (write_ref_to_lockfile(lock, orig_sha1) ||
-	    commit_ref_update(lock, orig_sha1, NULL))
-		error("unable to write current sha1 into %s", oldrefname);
+	if (write_ref_to_lockfile(lock, orig_sha1, &err) ||
+	    commit_ref_update(lock, orig_sha1, NULL, &err)) {
+		error("unable to write current sha1 into %s: %s", oldrefname, err.buf);
+		strbuf_release(&err);
+	}
 	log_all_ref_updates = flag;
 
  rollbacklog:
@@ -3113,8 +3118,8 @@ static int copy_msg(char *buf, const char *msg)
 	return cp - buf;
 }
 
-/* This function must set a meaningful errno on failure */
-int log_ref_setup(const char *refname, struct strbuf *sb_logfile)
+/* This function will fill in *err and return -1 on failure */
+int log_ref_setup(const char *refname, struct strbuf *sb_logfile, struct strbuf *err)
 {
 	int logfd, oflags = O_APPEND | O_WRONLY;
 	char *logfile;
@@ -3129,9 +3134,8 @@ int log_ref_setup(const char *refname, struct strbuf *sb_logfile)
 	     starts_with(refname, "refs/notes/") ||
 	     !strcmp(refname, "HEAD"))) {
 		if (safe_create_leading_directories(logfile) < 0) {
-			int save_errno = errno;
-			error("unable to create directory for %s", logfile);
-			errno = save_errno;
+			strbuf_addf(err, "unable to create directory for %s. "
+				    "%s", logfile, strerror(errno));
 			return -1;
 		}
 		oflags |= O_CREAT;
@@ -3144,20 +3148,16 @@ int log_ref_setup(const char *refname, struct strbuf *sb_logfile)
 
 		if (errno == EISDIR) {
 			if (remove_empty_directories(logfile)) {
-				int save_errno = errno;
-				error("There are still logs under '%s'",
-				      logfile);
-				errno = save_errno;
+				strbuf_addf(err, "There are still logs under "
+					    "'%s'", logfile);
 				return -1;
 			}
 			logfd = open(logfile, oflags, 0666);
 		}
 
 		if (logfd < 0) {
-			int save_errno = errno;
-			error("Unable to append to %s: %s", logfile,
-			      strerror(errno));
-			errno = save_errno;
+			strbuf_addf(err, "Unable to append to %s: %s",
+				    logfile, strerror(errno));
 			return -1;
 		}
 	}
@@ -3195,7 +3195,7 @@ static int log_ref_write_fd(int fd, const unsigned char *old_sha1,
 
 static int log_ref_write_1(const char *refname, const unsigned char *old_sha1,
 			   const unsigned char *new_sha1, const char *msg,
-			   struct strbuf *sb_log_file)
+			   struct strbuf *sb_log_file, struct strbuf *err)
 {
 	int logfd, result, oflags = O_APPEND | O_WRONLY;
 	char *log_file;
@@ -3203,7 +3203,8 @@ static int log_ref_write_1(const char *refname, const unsigned char *old_sha1,
 	if (log_all_ref_updates < 0)
 		log_all_ref_updates = !is_bare_repository();
 
-	result = log_ref_setup(refname, sb_log_file);
+	result = log_ref_setup(refname, sb_log_file, err);
+
 	if (result)
 		return result;
 	log_file = sb_log_file->buf;
@@ -3216,26 +3217,25 @@ static int log_ref_write_1(const char *refname, const unsigned char *old_sha1,
 	result = log_ref_write_fd(logfd, old_sha1, new_sha1,
 				  git_committer_info(0), msg);
 	if (result) {
-		int save_errno = errno;
 		close(logfd);
-		error("Unable to append to %s", log_file);
-		errno = save_errno;
+		strbuf_addf(err, "Unable to append to %s. %s", log_file,
+			    strerror(errno));
 		return -1;
 	}
 	if (close(logfd)) {
-		int save_errno = errno;
-		error("Unable to append to %s", log_file);
-		errno = save_errno;
+		strbuf_addf(err, "Unable to append to %s. %s", log_file,
+			    strerror(errno));
 		return -1;
 	}
 	return 0;
 }
 
 static int log_ref_write(const char *refname, const unsigned char *old_sha1,
-			 const unsigned char *new_sha1, const char *msg)
+			 const unsigned char *new_sha1, const char *msg,
+			 struct strbuf *err)
 {
 	struct strbuf sb = STRBUF_INIT;
-	int ret = log_ref_write_1(refname, old_sha1, new_sha1, msg, &sb);
+	int ret = log_ref_write_1(refname, old_sha1, new_sha1, msg, &sb, err);
 	strbuf_release(&sb);
 	return ret;
 }
@@ -3247,25 +3247,28 @@ int is_branch(const char *refname)
 
 /*
  * Write sha1 into the open lockfile, then close the lockfile. On
- * errors, rollback the lockfile and set errno to reflect the problem.
+ * errors, rollback the lockfile, fill in *err and
+ * return -1.
  */
 static int write_ref_to_lockfile(struct ref_lock *lock,
-				 const unsigned char *sha1)
+				 const unsigned char *sha1, struct strbuf *err)
 {
 	static char term = '\n';
 	struct object *o;
 
 	o = parse_object(sha1);
 	if (!o) {
-		error("Trying to write ref %s with nonexistent object %s",
-			lock->ref_name, sha1_to_hex(sha1));
+		strbuf_addf(err,
+			    "Trying to write ref %s with nonexistent object %s",
+			    lock->ref_name, sha1_to_hex(sha1));
 		unlock_ref(lock);
 		errno = EINVAL;
 		return -1;
 	}
 	if (o->type != OBJ_COMMIT && is_branch(lock->ref_name)) {
-		error("Trying to write non-commit object %s to branch %s",
-			sha1_to_hex(sha1), lock->ref_name);
+		strbuf_addf(err,
+			    "Trying to write non-commit object %s to branch %s",
+			    sha1_to_hex(sha1), lock->ref_name);
 		unlock_ref(lock);
 		errno = EINVAL;
 		return -1;
@@ -3273,10 +3276,9 @@ static int write_ref_to_lockfile(struct ref_lock *lock,
 	if (write_in_full(lock->lk->fd, sha1_to_hex(sha1), 40) != 40 ||
 	    write_in_full(lock->lk->fd, &term, 1) != 1 ||
 	    close_ref(lock) < 0) {
-		int save_errno = errno;
-		error("Couldn't write %s", lock->lk->filename.buf);
+		strbuf_addf(err,
+			    "Couldn't write %s", lock->lk->filename.buf);
 		unlock_ref(lock);
-		errno = save_errno;
 		return -1;
 	}
 	return 0;
@@ -3288,12 +3290,15 @@ static int write_ref_to_lockfile(struct ref_lock *lock,
  * necessary, using the specified lockmsg (which can be NULL).
  */
 static int commit_ref_update(struct ref_lock *lock,
-			     const unsigned char *sha1, const char *logmsg)
+			     const unsigned char *sha1, const char *logmsg,
+			     struct strbuf *err)
 {
 	clear_loose_ref_cache(&ref_cache);
-	if (log_ref_write(lock->ref_name, lock->old_oid.hash, sha1, logmsg) < 0 ||
+	if (log_ref_write(lock->ref_name, lock->old_oid.hash, sha1, logmsg, err) < 0 ||
 	    (strcmp(lock->ref_name, lock->orig_ref_name) &&
-	     log_ref_write(lock->orig_ref_name, lock->old_oid.hash, sha1, logmsg) < 0)) {
+	     log_ref_write(lock->orig_ref_name, lock->old_oid.hash, sha1, logmsg, err) < 0)) {
+		strbuf_addf(err, "Cannot update the ref '%s'.",
+			    lock->ref_name);
 		unlock_ref(lock);
 		return -1;
 	}
@@ -3317,7 +3322,8 @@ static int commit_ref_update(struct ref_lock *lock,
 					      head_sha1, &head_flag);
 		if (head_ref && (head_flag & REF_ISSYMREF) &&
 		    !strcmp(head_ref, lock->ref_name))
-			log_ref_write("HEAD", lock->old_oid.hash, sha1, logmsg);
+			log_ref_write("HEAD", lock->old_oid.hash, sha1, logmsg,
+				      err);
 	}
 	if (commit_ref(lock)) {
 		error("Couldn't set %s", lock->ref_name);
@@ -3336,6 +3342,7 @@ int create_symref(const char *ref_target, const char *refs_heads_master,
 	int fd, len, written;
 	char *git_HEAD = git_pathdup("%s", ref_target);
 	unsigned char old_sha1[20], new_sha1[20];
+	struct strbuf err = STRBUF_INIT;
 
 	if (logmsg && read_ref(ref_target, old_sha1))
 		hashclr(old_sha1);
@@ -3384,8 +3391,11 @@ int create_symref(const char *ref_target, const char *refs_heads_master,
 #ifndef NO_SYMLINK_HEAD
 	done:
 #endif
-	if (logmsg && !read_ref(refs_heads_master, new_sha1))
-		log_ref_write(ref_target, old_sha1, new_sha1, logmsg);
+	if (logmsg && !read_ref(refs_heads_master, new_sha1) &&
+		log_ref_write(ref_target, old_sha1, new_sha1, logmsg, &err)) {
+		error("%s", err.buf);
+		strbuf_release(&err);
+	}
 
 	free(git_HEAD);
 	return 0;
@@ -4021,14 +4031,13 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 				 * value, so we don't need to write it.
 				 */
 			} else if (write_ref_to_lockfile(update->lock,
-							 update->new_sha1)) {
+							 update->new_sha1,
+							 err)) {
 				/*
 				 * The lock was freed upon failure of
 				 * write_ref_to_lockfile():
 				 */
 				update->lock = NULL;
-				strbuf_addf(err, "cannot update the ref '%s'.",
-					    update->refname);
 				ret = TRANSACTION_GENERIC_ERROR;
 				goto cleanup;
 			} else {
@@ -4054,11 +4063,9 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 
 		if (update->flags & REF_NEEDS_COMMIT) {
 			if (commit_ref_update(update->lock,
-					      update->new_sha1, update->msg)) {
+					      update->new_sha1, update->msg, err)) {
 				/* freed by commit_ref_update(): */
 				update->lock = NULL;
-				strbuf_addf(err, "Cannot update the ref '%s'.",
-					    update->refname);
 				ret = TRANSACTION_GENERIC_ERROR;
 				goto cleanup;
 			} else {
diff --git a/refs.h b/refs.h
index e82fca5..debdefc 100644
--- a/refs.h
+++ b/refs.h
@@ -226,9 +226,9 @@ int pack_refs(unsigned int flags);
 #define REF_NODEREF	0x01
 
 /*
- * Setup reflog before using. Set errno to something meaningful on failure.
+ * Setup reflog before using. Fill in err and return -1 on failure.
  */
-int log_ref_setup(const char *refname, struct strbuf *logfile);
+int log_ref_setup(const char *refname, struct strbuf *logfile, struct strbuf *err);
 
 /** Reads log for the value of ref during at_time. **/
 extern int read_ref_at(const char *refname, unsigned int flags,
-- 
2.0.4.314.gdbf7a51-twtrsrc