[PATCH v5 00/30] Use ref transactions for all ref updates

[PATCH v5 00/30] Use ref transactions for all ref updates

[Ronnie Sahlberg]

This patch series is based on mhagger/ref-transactions and expands on the
transaction API. It converts all external (outside of refs.c) callers to
use the transaction API for any writes.
This makes most of the ref updates to become atomic when there are failures
locking or writing to a ref.

Version 5:
 - Reword commit messages for having _create/_delete/_update returning
   success/failure. There are no conditions yet that return an error from
   these failures but there will be in the future. So we still check the
   return from these functions in the callers in preparation for this.
 - Don't leak memory by just passing a strbuf_detach() pointer to functions.
   Use <obj>.buf and explicitely strbuf_release the data afterwards.
 - Remove the function update_ref_lock.
 - Remove the function update_ref_write.
 - Track transaction status and die(BUG:) if we call _create/_delete/_update/
   _commit for a transaction that is not OPEN.

Version 4:
 - Rename patch series from "Use ref transactions from most callers" to
   "Use ref transactions for all ref updates".
 - Convert all external ref writes to use transactions and make write_ref_sha1
   and lock_ref_sha1 static functions.
 - Change the ref commit and free handling so we no longer pass pointer to
   pointer to _commit. _commit no longer frees the transaction. The caller
   MUST call _free itself.
 - Change _commit to take a strbuf pointer instead of a char* for error
   reporting back to the caller.
 - Re-add the walker patch after fixing it.

Version 3:
 - Remove the walker patch for now. Walker needs more complex solution
   so defer it until the basics are done.
 - Remove the onerr argument to ref_transaction_commit(). All callers
   that need to die() on error now have to do this explicitely.
 - Pass an error string from ref_transaction_commit() back to the callers
   so that they can craft a nice error message upon failures.
 - Make ref_transaction_rollback() accept NULL as argument.
 - Change ref_transaction_commit() to take a pointer to pointer argument for
   the transaction and have it clear the callers pointer to NULL when
   invoked. This allows for much nicer handling of transaction rollback on
   failure.

Version 2:
 - Add a patch to ref_transaction_commit to make it honor onerr even if the
   error triggered in ref_Transaction_commit itself rather than in a call
   to other functions (that already honor onerr).
 - Add a patch to make the update_ref() helper function use transactions
   internally.
 - Change ref_transaction_update to die() instead of error() if we pass
   if a NULL old_sha1 but have have_old == true.
 - Change ref_transaction_create to die() instead of error() if new_sha1
   is false but we pass it a null_sha1.
 - Change ref_transaction_delete die() instead of error() if we pass
   if a NULL old_sha1 but have have_old == true.
 - Change several places to do  if(!transaction || ref_transaction_update()
   || ref_Transaction_commit()) die(generic-message) instead of checking each
   step separately and having a different message for each failure.
   Most users are likely not interested in what step of the transaction
   failed and only whether it failed or not.
 - Change commit.c to only pass a pointer to ref_transaction_update
   iff current_head is non-NULL.
   The previous patch used to compute a garbage pointer for
   current_head->object.sha1 and relied on the fact that ref_transaction_update
   would not try to dereference this pointer if !!current_head was 0.
 - Updated commit message for the walker_fetch change to try to justify why
   the change in locking semantics should not be harmful.

Ronnie Sahlberg (30):
  refs.c: constify the sha arguments for
    ref_transaction_create|delete|update
  refs.c: allow passing NULL to ref_transaction_free
  refs.c: add a strbuf argument to ref_transaction_commit for error
    logging
  refs.c: make ref_update_reject_duplicates take a strbuf argument for
    errors
  update-ref.c: log transaction error from the update_ref
  refs.c: make update_ref_write update a strbuf on failure
  refs.c: remove the onerr argument to ref_transaction_commit
  refs.c: change ref_transaction_update() to do error checking and
    return status
  refs.c: change ref_transaction_create to do error checking and return
    status
  refs.c: ref_transaction_delete to check for error and return status
  tag.c: use ref transactions when doing updates
  replace.c: use the ref transaction functions for updates
  commit.c: use ref transactions for updates
  sequencer.c: use ref transactions for all ref updates
  fast-import.c: change update_branch to use ref transactions
  branch.c: use ref transaction for all ref updates
  refs.c: change update_ref to use a transaction
  refs.c: free the transaction before returning when number of updates
    is 0
  refs.c: ref_transaction_commit should not free the transaction
  fetch.c: clear errno before calling functions that might set it
  fetch.c: change s_update_ref to use a ref transaction
  fetch.c: use a single ref transaction for all ref updates
  receive-pack.c: use a reference transaction for updating the refs
  fast-import.c: use a ref transaction when dumping tags
  walker.c: use ref transaction for ref updates
  refs.c: make write_ref_sha1 static
  refs.c: make lock_ref_sha1 static
  refs.c: add transaction.status and track OPEN/CLOSED/ERROR
  refs.c: remove the update_ref_lock function
  refs.c: remove the update_ref_write function

 branch.c               |  31 ++++----
 builtin/commit.c       |  24 +++---
 builtin/fetch.c        |  35 ++++-----
 builtin/receive-pack.c |  20 ++---
 builtin/replace.c      |  15 ++--
 builtin/tag.c          |  15 ++--
 builtin/update-ref.c   |  29 +++++---
 fast-import.c          |  38 ++++++----
 refs.c                 | 193 +++++++++++++++++++++++++++++--------------------
 refs.h                 |  45 ++++++------
 sequencer.c            |  24 ++++--
 walker.c               |  51 ++++++-------
 12 files changed, 297 insertions(+), 223 deletions(-)

-- 
1.9.1.532.gf8485a6

[PATCH v5 01/30] refs.c: constify the sha arguments for ref_transaction_create|delete|update

[Ronnie Sahlberg]

ref_transaction_create|delete|update has no need to modify the sha1
arguments passed to it so it should use const unsigned char* instead
of unsigned char*.

Some functions, such as fast_forward_to(), already have its old/new
sha1 arguments as consts. This function will at some point need to
use ref_transaction_update() in which case this change is required.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 refs.c | 7 ++++---
 refs.h | 7 ++++---
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/refs.c b/refs.c
index 728a761..138ab70 100644
--- a/refs.c
+++ b/refs.c
@@ -3329,7 +3329,8 @@ static struct ref_update *add_update(struct ref_transaction *transaction,
 
 void ref_transaction_update(struct ref_transaction *transaction,
 			    const char *refname,
-			    unsigned char *new_sha1, unsigned char *old_sha1,
+			    const unsigned char *new_sha1,
+			    const unsigned char *old_sha1,
 			    int flags, int have_old)
 {
 	struct ref_update *update = add_update(transaction, refname);
@@ -3343,7 +3344,7 @@ void ref_transaction_update(struct ref_transaction *transaction,
 
 void ref_transaction_create(struct ref_transaction *transaction,
 			    const char *refname,
-			    unsigned char *new_sha1,
+			    const unsigned char *new_sha1,
 			    int flags)
 {
 	struct ref_update *update = add_update(transaction, refname);
@@ -3357,7 +3358,7 @@ void ref_transaction_create(struct ref_transaction *transaction,
 
 void ref_transaction_delete(struct ref_transaction *transaction,
 			    const char *refname,
-			    unsigned char *old_sha1,
+			    const unsigned char *old_sha1,
 			    int flags, int have_old)
 {
 	struct ref_update *update = add_update(transaction, refname);
diff --git a/refs.h b/refs.h
index 0f08def..892c5b6 100644
--- a/refs.h
+++ b/refs.h
@@ -239,7 +239,8 @@ void ref_transaction_rollback(struct ref_transaction *transaction);
  */
 void ref_transaction_update(struct ref_transaction *transaction,
 			    const char *refname,
-			    unsigned char *new_sha1, unsigned char *old_sha1,
+			    const unsigned char *new_sha1,
+			    const unsigned char *old_sha1,
 			    int flags, int have_old);
 
 /*
@@ -250,7 +251,7 @@ void ref_transaction_update(struct ref_transaction *transaction,
  */
 void ref_transaction_create(struct ref_transaction *transaction,
 			    const char *refname,
-			    unsigned char *new_sha1,
+			    const unsigned char *new_sha1,
 			    int flags);
 
 /*
@@ -260,7 +261,7 @@ void ref_transaction_create(struct ref_transaction *transaction,
  */
 void ref_transaction_delete(struct ref_transaction *transaction,
 			    const char *refname,
-			    unsigned char *old_sha1,
+			    const unsigned char *old_sha1,
 			    int flags, int have_old);
 
 /*
-- 
1.9.1.532.gf8485a6

[PATCH v5 02/30] refs.c: allow passing NULL to ref_transaction_free

[Ronnie Sahlberg]

Allow ref_transaction_free to be called with NULL and in extension allow
ref_transaction_rollback to be called for a NULL transaction.

This allows us to write code that will
  if ( (!transaction ||
        ref_transaction_update(...))  ||
      (ref_transaction_commit(...) && !(transaction = NULL)) {
          ref_transaction_rollback(transaction);
          ...
  }

In this case transaction is reset to NULL IFF ref_transaction_commit() was
invoked and thus the rollback becomes ref_transaction_rollback(NULL) which
is safe. IF the conditional triggered prior to ref_transaction_commit()
then transaction is untouched and then ref_transaction_rollback(transaction)
will rollback the failed transaction.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 refs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/refs.c b/refs.c
index 138ab70..2d83ef6 100644
--- a/refs.c
+++ b/refs.c
@@ -3303,6 +3303,9 @@ static void ref_transaction_free(struct ref_transaction *transaction)
 {
 	int i;
 
+	if (!transaction)
+		return;
+
 	for (i = 0; i < transaction->nr; i++)
 		free(transaction->updates[i]);
 
-- 
1.9.1.532.gf8485a6

[PATCH v5 03/30] refs.c: add a strbuf argument to ref_transaction_commit for error logging

[Ronnie Sahlberg]

Add a strbuf argument to _commit so that we can pass an error string back to
the caller. So that we can do error logging from the caller instead of from
_commit.

Longer term plan is to first convert all callers to use onerr==QUIET_ON_ERR
and craft any log messages from the callers themselves and finally remove the
onerr argument completely.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 builtin/update-ref.c | 2 +-
 refs.c               | 6 +++++-
 refs.h               | 5 ++++-
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 405267f..aaa06aa 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -367,7 +367,7 @@ int cmd_update_ref(int argc, const char **argv, const char *prefix)
 		if (end_null)
 			line_termination = '\0';
 		update_refs_stdin();
-		ret = ref_transaction_commit(transaction, msg,
+		ret = ref_transaction_commit(transaction, msg, NULL,
 					     UPDATE_REFS_DIE_ON_ERR);
 		return ret;
 	}
diff --git a/refs.c b/refs.c
index 2d83ef6..64e8feb 100644
--- a/refs.c
+++ b/refs.c
@@ -3414,7 +3414,8 @@ static int ref_update_reject_duplicates(struct ref_update **updates, int n,
 }
 
 int ref_transaction_commit(struct ref_transaction *transaction,
-			   const char *msg, enum action_on_err onerr)
+			   const char *msg, struct strbuf *err,
+			   enum action_on_err onerr)
 {
 	int ret = 0, delnum = 0, i;
 	const char **delnames;
@@ -3443,6 +3444,9 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 					       update->flags,
 					       &update->type, onerr);
 		if (!update->lock) {
+			if (err)
+				strbuf_addf(err ,"Cannot lock the ref '%s'.",
+					    update->refname);
 			ret = 1;
 			goto cleanup;
 		}
diff --git a/refs.h b/refs.h
index 892c5b6..ff87e14 100644
--- a/refs.h
+++ b/refs.h
@@ -268,9 +268,12 @@ void ref_transaction_delete(struct ref_transaction *transaction,
  * Commit all of the changes that have been queued in transaction, as
  * atomically as possible.  Return a nonzero value if there is a
  * problem.  The ref_transaction is freed by this function.
+ * If err is non-NULL we will add an error string to it to explain why
+ * the transaction failed.
  */
 int ref_transaction_commit(struct ref_transaction *transaction,
-			   const char *msg, enum action_on_err onerr);
+			   const char *msg, struct strbuf *err,
+			   enum action_on_err onerr);
 
 /** Lock a ref and then write its file */
 int update_ref(const char *action, const char *refname,
-- 
1.9.1.532.gf8485a6

[PATCH v5 04/30] refs.c: make ref_update_reject_duplicates take a strbuf argument for errors

[Ronnie Sahlberg]

Make ref_update_reject_duplicates return any error that occurs through a
new strbuf argument.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 refs.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/refs.c b/refs.c
index 64e8feb..21a147b 100644
--- a/refs.c
+++ b/refs.c
@@ -3393,6 +3393,7 @@ static int ref_update_compare(const void *r1, const void *r2)
 }
 
 static int ref_update_reject_duplicates(struct ref_update **updates, int n,
+					struct strbuf *err,
 					enum action_on_err onerr)
 {
 	int i;
@@ -3400,6 +3401,9 @@ static int ref_update_reject_duplicates(struct ref_update **updates, int n,
 		if (!strcmp(updates[i - 1]->refname, updates[i]->refname)) {
 			const char *str =
 				"Multiple updates for ref '%s' not allowed.";
+			if (err)
+				strbuf_addf(err, str, updates[i]->refname);
+
 			switch (onerr) {
 			case UPDATE_REFS_MSG_ON_ERR:
 				error(str, updates[i]->refname); break;
@@ -3430,7 +3434,7 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 
 	/* Copy, sort, and reject duplicate refs */
 	qsort(updates, n, sizeof(*updates), ref_update_compare);
-	ret = ref_update_reject_duplicates(updates, n, onerr);
+	ret = ref_update_reject_duplicates(updates, n, err, onerr);
 	if (ret)
 		goto cleanup;
 
-- 
1.9.1.532.gf8485a6

[PATCH v5 05/30] update-ref.c: log transaction error from the update_ref

[Ronnie Sahlberg]

Call ref_transaction_commit with QUIET_ON_ERR and use the strbuf that is
returned to print a log message if/after the transaction fails.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 builtin/update-ref.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index aaa06aa..207e24d 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -342,6 +342,7 @@ int cmd_update_ref(int argc, const char **argv, const char *prefix)
 	const char *refname, *oldval, *msg = NULL;
 	unsigned char sha1[20], oldsha1[20];
 	int delete = 0, no_deref = 0, read_stdin = 0, end_null = 0, flags = 0;
+	struct strbuf err = STRBUF_INIT;
 	struct option options[] = {
 		OPT_STRING( 'm', NULL, &msg, N_("reason"), N_("reason of the update")),
 		OPT_BOOL('d', NULL, &delete, N_("delete the reference")),
@@ -359,17 +360,16 @@ int cmd_update_ref(int argc, const char **argv, const char *prefix)
 		die("Refusing to perform update with empty message.");
 
 	if (read_stdin) {
-		int ret;
 		transaction = ref_transaction_begin();
-
 		if (delete || no_deref || argc > 0)
 			usage_with_options(git_update_ref_usage, options);
 		if (end_null)
 			line_termination = '\0';
 		update_refs_stdin();
-		ret = ref_transaction_commit(transaction, msg, NULL,
-					     UPDATE_REFS_DIE_ON_ERR);
-		return ret;
+		if (ref_transaction_commit(transaction, msg, &err,
+					   UPDATE_REFS_QUIET_ON_ERR))
+			die("%s", err.buf);
+		return 0;
 	}
 
 	if (end_null)
-- 
1.9.1.532.gf8485a6

[PATCH v5 06/30] refs.c: make update_ref_write update a strbuf on failure

[Ronnie Sahlberg]

Change update_ref_write to also update an error strbuf on failure.
This makes the error available to ref_transaction_commit callers if the
transaction failed due to update_ref_sha1/write_ref_sha1 failures.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 refs.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/refs.c b/refs.c
index 21a147b..5e06fd9 100644
--- a/refs.c
+++ b/refs.c
@@ -3253,10 +3253,13 @@ static struct ref_lock *update_ref_lock(const char *refname,
 
 static int update_ref_write(const char *action, const char *refname,
 			    const unsigned char *sha1, struct ref_lock *lock,
-			    enum action_on_err onerr)
+			    struct strbuf *err, enum action_on_err onerr)
 {
 	if (write_ref_sha1(lock, sha1, action) < 0) {
 		const char *str = "Cannot update the ref '%s'.";
+		if (err)
+			strbuf_addf(err, str, refname);
+
 		switch (onerr) {
 		case UPDATE_REFS_MSG_ON_ERR: error(str, refname); break;
 		case UPDATE_REFS_DIE_ON_ERR: die(str, refname); break;
@@ -3382,7 +3385,7 @@ int update_ref(const char *action, const char *refname,
 	lock = update_ref_lock(refname, oldval, flags, NULL, onerr);
 	if (!lock)
 		return 1;
-	return update_ref_write(action, refname, sha1, lock, onerr);
+	return update_ref_write(action, refname, sha1, lock, NULL, onerr);
 }
 
 static int ref_update_compare(const void *r1, const void *r2)
@@ -3464,7 +3467,7 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 			ret = update_ref_write(msg,
 					       update->refname,
 					       update->new_sha1,
-					       update->lock, onerr);
+					       update->lock, err, onerr);
 			update->lock = NULL; /* freed by update_ref_write */
 			if (ret)
 				goto cleanup;
-- 
1.9.1.532.gf8485a6

[PATCH v5 07/30] refs.c: remove the onerr argument to ref_transaction_commit

[Ronnie Sahlberg]

Since all callers now use QUIET_ON_ERR we no longer need to provide an onerr
argument any more. Remove the onerr argument from the ref_transaction_commit
signature.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 builtin/update-ref.c |  3 +--
 refs.c               | 22 +++++++---------------
 refs.h               |  3 +--
 3 files changed, 9 insertions(+), 19 deletions(-)

diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 207e24d..2bef2a0 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -366,8 +366,7 @@ int cmd_update_ref(int argc, const char **argv, const char *prefix)
 		if (end_null)
 			line_termination = '\0';
 		update_refs_stdin();
-		if (ref_transaction_commit(transaction, msg, &err,
-					   UPDATE_REFS_QUIET_ON_ERR))
+		if (ref_transaction_commit(transaction, msg, &err))
 			die("%s", err.buf);
 		return 0;
 	}
diff --git a/refs.c b/refs.c
index 5e06fd9..308e13e 100644
--- a/refs.c
+++ b/refs.c
@@ -3396,8 +3396,7 @@ static int ref_update_compare(const void *r1, const void *r2)
 }
 
 static int ref_update_reject_duplicates(struct ref_update **updates, int n,
-					struct strbuf *err,
-					enum action_on_err onerr)
+					struct strbuf *err)
 {
 	int i;
 	for (i = 1; i < n; i++)
@@ -3407,22 +3406,13 @@ static int ref_update_reject_duplicates(struct ref_update **updates, int n,
 			if (err)
 				strbuf_addf(err, str, updates[i]->refname);
 
-			switch (onerr) {
-			case UPDATE_REFS_MSG_ON_ERR:
-				error(str, updates[i]->refname); break;
-			case UPDATE_REFS_DIE_ON_ERR:
-				die(str, updates[i]->refname); break;
-			case UPDATE_REFS_QUIET_ON_ERR:
-				break;
-			}
 			return 1;
 		}
 	return 0;
 }
 
 int ref_transaction_commit(struct ref_transaction *transaction,
-			   const char *msg, struct strbuf *err,
-			   enum action_on_err onerr)
+			   const char *msg, struct strbuf *err)
 {
 	int ret = 0, delnum = 0, i;
 	const char **delnames;
@@ -3437,7 +3427,7 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 
 	/* Copy, sort, and reject duplicate refs */
 	qsort(updates, n, sizeof(*updates), ref_update_compare);
-	ret = ref_update_reject_duplicates(updates, n, err, onerr);
+	ret = ref_update_reject_duplicates(updates, n, err);
 	if (ret)
 		goto cleanup;
 
@@ -3449,7 +3439,8 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 					       (update->have_old ?
 						update->old_sha1 : NULL),
 					       update->flags,
-					       &update->type, onerr);
+					       &update->type,
+					       UPDATE_REFS_QUIET_ON_ERR);
 		if (!update->lock) {
 			if (err)
 				strbuf_addf(err ,"Cannot lock the ref '%s'.",
@@ -3467,7 +3458,8 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 			ret = update_ref_write(msg,
 					       update->refname,
 					       update->new_sha1,
-					       update->lock, err, onerr);
+					       update->lock, err,
+					       UPDATE_REFS_QUIET_ON_ERR);
 			update->lock = NULL; /* freed by update_ref_write */
 			if (ret)
 				goto cleanup;
diff --git a/refs.h b/refs.h
index ff87e14..bc7715e 100644
--- a/refs.h
+++ b/refs.h
@@ -272,8 +272,7 @@ void ref_transaction_delete(struct ref_transaction *transaction,
  * the transaction failed.
  */
 int ref_transaction_commit(struct ref_transaction *transaction,
-			   const char *msg, struct strbuf *err,
-			   enum action_on_err onerr);
+			   const char *msg, struct strbuf *err);
 
 /** Lock a ref and then write its file */
 int update_ref(const char *action, const char *refname,
-- 
1.9.1.532.gf8485a6

[PATCH v5 08/30] refs.c: change ref_transaction_update() to do error checking and return status

[Ronnie Sahlberg]

Update ref_transaction_update() do some basic error checking and return
true on error. Update all callers to check ref_transaction_update() for error.
There are currently no conditions in _update that will return error but there
will be in the future.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 builtin/update-ref.c | 10 ++++++----
 refs.c               |  9 +++++++--
 refs.h               | 10 +++++-----
 3 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 2bef2a0..59c4d6b 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -197,8 +197,9 @@ static const char *parse_cmd_update(struct strbuf *input, const char *next)
 	if (*next != line_termination)
 		die("update %s: extra input: %s", refname, next);
 
-	ref_transaction_update(transaction, refname, new_sha1, old_sha1,
-			       update_flags, have_old);
+	if (ref_transaction_update(transaction, refname, new_sha1, old_sha1,
+				   update_flags, have_old))
+		die("update %s: failed", refname);
 
 	update_flags = 0;
 	free(refname);
@@ -286,8 +287,9 @@ static const char *parse_cmd_verify(struct strbuf *input, const char *next)
 	if (*next != line_termination)
 		die("verify %s: extra input: %s", refname, next);
 
-	ref_transaction_update(transaction, refname, new_sha1, old_sha1,
-			       update_flags, have_old);
+	if (ref_transaction_update(transaction, refname, new_sha1, old_sha1,
+				   update_flags, have_old))
+		die("failed transaction update for %s", refname);
 
 	update_flags = 0;
 	free(refname);
diff --git a/refs.c b/refs.c
index 308e13e..1a903fb 100644
--- a/refs.c
+++ b/refs.c
@@ -3333,19 +3333,24 @@ static struct ref_update *add_update(struct ref_transaction *transaction,
 	return update;
 }
 
-void ref_transaction_update(struct ref_transaction *transaction,
+int ref_transaction_update(struct ref_transaction *transaction,
 			    const char *refname,
 			    const unsigned char *new_sha1,
 			    const unsigned char *old_sha1,
 			    int flags, int have_old)
 {
-	struct ref_update *update = add_update(transaction, refname);
+	struct ref_update *update;
+
+	if (have_old && !old_sha1)
+		die("have_old is true but old_sha1 is NULL");
 
+	update = add_update(transaction, refname);
 	hashcpy(update->new_sha1, new_sha1);
 	update->flags = flags;
 	update->have_old = have_old;
 	if (have_old)
 		hashcpy(update->old_sha1, old_sha1);
+	return 0;
 }
 
 void ref_transaction_create(struct ref_transaction *transaction,
diff --git a/refs.h b/refs.h
index bc7715e..0364a3e 100644
--- a/refs.h
+++ b/refs.h
@@ -237,11 +237,11 @@ void ref_transaction_rollback(struct ref_transaction *transaction);
  * that the reference should have had before the update, or zeros if
  * it must not have existed beforehand.
  */
-void ref_transaction_update(struct ref_transaction *transaction,
-			    const char *refname,
-			    const unsigned char *new_sha1,
-			    const unsigned char *old_sha1,
-			    int flags, int have_old);
+int ref_transaction_update(struct ref_transaction *transaction,
+			   const char *refname,
+			   const unsigned char *new_sha1,
+			   const unsigned char *old_sha1,
+			   int flags, int have_old);
 
 /*
  * Add a reference creation to transaction.  new_sha1 is the value
-- 
1.9.1.532.gf8485a6

[PATCH v5 09/30] refs.c: change ref_transaction_create to do error checking and return status

[Ronnie Sahlberg]

Do basic error checking in ref_transaction_create() and make it return
status. Update all callers to check the result of ref_transaction_create()
There are currently no conditions in _update that will return error but there
will be in the future.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 builtin/update-ref.c |  4 +++-
 refs.c               | 17 +++++++++++------
 refs.h               |  8 ++++----
 3 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 59c4d6b..3fab810 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -225,7 +225,9 @@ static const char *parse_cmd_create(struct strbuf *input, const char *next)
 	if (*next != line_termination)
 		die("create %s: extra input: %s", refname, next);
 
-	ref_transaction_create(transaction, refname, new_sha1, update_flags);
+	if (ref_transaction_create(transaction, refname, new_sha1,
+				   update_flags))
+		die("failed transaction create for %s", refname);
 
 	update_flags = 0;
 	free(refname);
diff --git a/refs.c b/refs.c
index 1a903fb..27db737 100644
--- a/refs.c
+++ b/refs.c
@@ -3353,18 +3353,23 @@ int ref_transaction_update(struct ref_transaction *transaction,
 	return 0;
 }
 
-void ref_transaction_create(struct ref_transaction *transaction,
-			    const char *refname,
-			    const unsigned char *new_sha1,
-			    int flags)
+int ref_transaction_create(struct ref_transaction *transaction,
+			   const char *refname,
+			   const unsigned char *new_sha1,
+			   int flags)
 {
-	struct ref_update *update = add_update(transaction, refname);
+	struct ref_update *update;
+
+	if (!new_sha1 || is_null_sha1(new_sha1))
+		die("create ref with null new_sha1");
+
+	update = add_update(transaction, refname);
 
-	assert(!is_null_sha1(new_sha1));
 	hashcpy(update->new_sha1, new_sha1);
 	hashclr(update->old_sha1);
 	update->flags = flags;
 	update->have_old = 1;
+	return 0;
 }
 
 void ref_transaction_delete(struct ref_transaction *transaction,
diff --git a/refs.h b/refs.h
index 0364a3e..01d773c 100644
--- a/refs.h
+++ b/refs.h
@@ -249,10 +249,10 @@ int ref_transaction_update(struct ref_transaction *transaction,
  * null SHA-1.  It is verified that the reference does not exist
  * already.
  */
-void ref_transaction_create(struct ref_transaction *transaction,
-			    const char *refname,
-			    const unsigned char *new_sha1,
-			    int flags);
+int ref_transaction_create(struct ref_transaction *transaction,
+			   const char *refname,
+			   const unsigned char *new_sha1,
+			   int flags);
 
 /*
  * Add a reference deletion to transaction.  If have_old is true, then
-- 
1.9.1.532.gf8485a6

[PATCH v5 10/30] refs.c: ref_transaction_delete to check for error and return status

[Ronnie Sahlberg]

Change ref_transaction_delete() to do basic error checking and return
status. Update all callers to check the return for ref_transaction_delete()
There are currently no conditions in _update that will return error but there
will be in the future.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 builtin/update-ref.c |  5 +++--
 refs.c               | 15 ++++++++++-----
 refs.h               |  8 ++++----
 3 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 3fab810..fc3512f 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -257,8 +257,9 @@ static const char *parse_cmd_delete(struct strbuf *input, const char *next)
 	if (*next != line_termination)
 		die("delete %s: extra input: %s", refname, next);
 
-	ref_transaction_delete(transaction, refname, old_sha1,
-			       update_flags, have_old);
+	if (ref_transaction_delete(transaction, refname, old_sha1,
+				   update_flags, have_old))
+		die("failed transaction delete for %s", refname);
 
 	update_flags = 0;
 	free(refname);
diff --git a/refs.c b/refs.c
index 27db737..0a4e28e 100644
--- a/refs.c
+++ b/refs.c
@@ -3372,19 +3372,24 @@ int ref_transaction_create(struct ref_transaction *transaction,
 	return 0;
 }
 
-void ref_transaction_delete(struct ref_transaction *transaction,
-			    const char *refname,
-			    const unsigned char *old_sha1,
-			    int flags, int have_old)
+int ref_transaction_delete(struct ref_transaction *transaction,
+			   const char *refname,
+			   const unsigned char *old_sha1,
+			   int flags, int have_old)
 {
-	struct ref_update *update = add_update(transaction, refname);
+	struct ref_update *update;
 
+	if (have_old && !old_sha1)
+		die("have_old is true but old_sha1 is NULL");
+
+	update = add_update(transaction, refname);
 	update->flags = flags;
 	update->have_old = have_old;
 	if (have_old) {
 		assert(!is_null_sha1(old_sha1));
 		hashcpy(update->old_sha1, old_sha1);
 	}
+	return 0;
 }
 
 int update_ref(const char *action, const char *refname,
diff --git a/refs.h b/refs.h
index 01d773c..5eb500e 100644
--- a/refs.h
+++ b/refs.h
@@ -259,10 +259,10 @@ int ref_transaction_create(struct ref_transaction *transaction,
  * old_sha1 holds the value that the reference should have had before
  * the update (which must not be the null SHA-1).
  */
-void ref_transaction_delete(struct ref_transaction *transaction,
-			    const char *refname,
-			    const unsigned char *old_sha1,
-			    int flags, int have_old);
+int ref_transaction_delete(struct ref_transaction *transaction,
+			   const char *refname,
+			   const unsigned char *old_sha1,
+			   int flags, int have_old);
 
 /*
  * Commit all of the changes that have been queued in transaction, as
-- 
1.9.1.532.gf8485a6

[PATCH v5 11/30] tag.c: use ref transactions when doing updates

[Ronnie Sahlberg]

Change tag.c to use ref transactions for all ref updates.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 builtin/tag.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/builtin/tag.c b/builtin/tag.c
index 40356e3..31e32cb 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -488,7 +488,6 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 	struct strbuf ref = STRBUF_INIT;
 	unsigned char object[20], prev[20];
 	const char *object_ref, *tag;
-	struct ref_lock *lock;
 	struct create_tag_options opt;
 	char *cleanup_arg = NULL;
 	int annotate = 0, force = 0, lines = -1;
@@ -496,6 +495,8 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 	const char *msgfile = NULL, *keyid = NULL;
 	struct msg_arg msg = { 0, STRBUF_INIT };
 	struct commit_list *with_commit = NULL;
+	struct ref_transaction *transaction;
+	struct strbuf err = STRBUF_INIT;
 	struct option options[] = {
 		OPT_CMDMODE('l', "list", &cmdmode, N_("list tag names"), 'l'),
 		{ OPTION_INTEGER, 'n', NULL, &lines, N_("n"),
@@ -641,11 +642,12 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 	if (annotate)
 		create_tag(object, tag, &buf, &opt, prev, object);
 
-	lock = lock_any_ref_for_update(ref.buf, prev, 0, NULL);
-	if (!lock)
-		die(_("%s: cannot lock the ref"), ref.buf);
-	if (write_ref_sha1(lock, object, NULL) < 0)
-		die(_("%s: cannot update the ref"), ref.buf);
+	transaction = ref_transaction_begin();
+	if (!transaction ||
+	    ref_transaction_update(transaction, ref.buf, object, prev,
+				   0, !is_null_sha1(prev)) ||
+	    ref_transaction_commit(transaction, NULL, &err))
+		die(_("%s: cannot update the ref: %s"), ref.buf, err.buf);
 	if (force && !is_null_sha1(prev) && hashcmp(prev, object))
 		printf(_("Updated tag '%s' (was %s)\n"), tag, find_unique_abbrev(prev, DEFAULT_ABBREV));
 
-- 
1.9.1.532.gf8485a6

[PATCH v5 12/30] replace.c: use the ref transaction functions for updates

[Ronnie Sahlberg]

Update replace.c to use ref transactions for updates.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 builtin/replace.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/builtin/replace.c b/builtin/replace.c
index b62420a..b037b29 100644
--- a/builtin/replace.c
+++ b/builtin/replace.c
@@ -129,7 +129,8 @@ static int replace_object(const char *object_ref, const char *replace_ref,
 	unsigned char object[20], prev[20], repl[20];
 	enum object_type obj_type, repl_type;
 	char ref[PATH_MAX];
-	struct ref_lock *lock;
+	struct ref_transaction *transaction;
+	struct strbuf err = STRBUF_INIT;
 
 	if (get_sha1(object_ref, object))
 		die("Failed to resolve '%s' as a valid ref.", object_ref);
@@ -157,11 +158,12 @@ static int replace_object(const char *object_ref, const char *replace_ref,
 	else if (!force)
 		die("replace ref '%s' already exists", ref);
 
-	lock = lock_any_ref_for_update(ref, prev, 0, NULL);
-	if (!lock)
-		die("%s: cannot lock the ref", ref);
-	if (write_ref_sha1(lock, repl, NULL) < 0)
-		die("%s: cannot update the ref", ref);
+	transaction = ref_transaction_begin();
+	if (!transaction ||
+	    ref_transaction_update(transaction, ref, repl, prev,
+				   0, !is_null_sha1(prev)) ||
+	    ref_transaction_commit(transaction, NULL, &err))
+		die(_("%s: failed to replace ref: %s"), ref, err.buf);
 
 	return 0;
 }
-- 
1.9.1.532.gf8485a6

[PATCH v5 13/30] commit.c: use ref transactions for updates

[Ronnie Sahlberg]

Change commit.c to use ref transactions for all ref updates.
Make sure we pass a NULL pointer to ref_transaction_update if have_old
is false.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 builtin/commit.c | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/builtin/commit.c b/builtin/commit.c
index d9550c5..a56f47a 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -1541,11 +1541,12 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	const char *index_file, *reflog_msg;
 	char *nl;
 	unsigned char sha1[20];
-	struct ref_lock *ref_lock;
 	struct commit_list *parents = NULL, **pptr = &parents;
 	struct stat statbuf;
 	struct commit *current_head = NULL;
 	struct commit_extra_header *extra = NULL;
+	struct ref_transaction *transaction;
+	struct strbuf err = STRBUF_INIT;
 
 	if (argc == 2 && !strcmp(argv[1], "-h"))
 		usage_with_options(builtin_commit_usage, builtin_commit_options);
@@ -1667,12 +1668,6 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	strbuf_release(&author_ident);
 	free_commit_extra_headers(extra);
 
-	ref_lock = lock_any_ref_for_update("HEAD",
-					   !current_head
-					   ? NULL
-					   : current_head->object.sha1,
-					   0, NULL);
-
 	nl = strchr(sb.buf, '\n');
 	if (nl)
 		strbuf_setlen(&sb, nl + 1 - sb.buf);
@@ -1681,13 +1676,15 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	strbuf_insert(&sb, 0, reflog_msg, strlen(reflog_msg));
 	strbuf_insert(&sb, strlen(reflog_msg), ": ", 2);
 
-	if (!ref_lock) {
-		rollback_index_files();
-		die(_("cannot lock HEAD ref"));
-	}
-	if (write_ref_sha1(ref_lock, sha1, sb.buf) < 0) {
+	transaction = ref_transaction_begin();
+	if (!transaction ||
+	    ref_transaction_update(transaction, "HEAD", sha1,
+				   current_head ?
+				   current_head->object.sha1 : NULL,
+				   0, !!current_head) ||
+	    ref_transaction_commit(transaction, sb.buf, &err)) {
 		rollback_index_files();
-		die(_("cannot update HEAD ref"));
+		die(_("HEAD: cannot update ref: %s"), err.buf);
 	}
 
 	unlink(git_path("CHERRY_PICK_HEAD"));
-- 
1.9.1.532.gf8485a6

[PATCH v5 14/30] sequencer.c: use ref transactions for all ref updates

[Ronnie Sahlberg]

Change to use ref transactions for all updates to refs.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 sequencer.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index bde5f04..9282a12 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -272,19 +272,31 @@ static int error_dirty_index(struct replay_opts *opts)
 static int fast_forward_to(const unsigned char *to, const unsigned char *from,
 			int unborn, struct replay_opts *opts)
 {
-	struct ref_lock *ref_lock;
+	struct ref_transaction *transaction;
 	struct strbuf sb = STRBUF_INIT;
-	int ret;
+	struct strbuf err = STRBUF_INIT;
 
 	read_cache();
 	if (checkout_fast_forward(from, to, 1))
 		exit(1); /* the callee should have complained already */
-	ref_lock = lock_any_ref_for_update("HEAD", unborn ? null_sha1 : from,
-					   0, NULL);
+
 	strbuf_addf(&sb, "%s: fast-forward", action_name(opts));
-	ret = write_ref_sha1(ref_lock, to, sb.buf);
+
+	transaction = ref_transaction_begin();
+	if ((!transaction ||
+	    ref_transaction_update(transaction, "HEAD", to, from,
+				   0, !unborn)) ||
+	    (ref_transaction_commit(transaction, sb.buf, &err) &&
+	     !(transaction = NULL))) {
+		ref_transaction_rollback(transaction);
+		error(_("HEAD: Could not fast-forward: %s\n"), err.buf);
+		strbuf_release(&sb);
+		strbuf_release(&err);
+		return -1;
+	}
+
 	strbuf_release(&sb);
-	return ret;
+	return 0;
 }
 
 static int do_recursive_merge(struct commit *base, struct commit *next,
-- 
1.9.1.532.gf8485a6

[PATCH v5 15/30] fast-import.c: change update_branch to use ref transactions

[Ronnie Sahlberg]

Change update_branch() to use ref transactions for updates.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 fast-import.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/fast-import.c b/fast-import.c
index fb4738d..35de36a 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -1678,36 +1678,41 @@ found_entry:
 static int update_branch(struct branch *b)
 {
 	static const char *msg = "fast-import";
-	struct ref_lock *lock;
+	struct ref_transaction *transaction;
 	unsigned char old_sha1[20];
+	struct strbuf err = STRBUF_INIT;
 
 	if (is_null_sha1(b->sha1))
 		return 0;
 	if (read_ref(b->name, old_sha1))
 		hashclr(old_sha1);
-	lock = lock_any_ref_for_update(b->name, old_sha1, 0, NULL);
-	if (!lock)
-		return error("Unable to lock %s", b->name);
 	if (!force_update && !is_null_sha1(old_sha1)) {
 		struct commit *old_cmit, *new_cmit;
 
 		old_cmit = lookup_commit_reference_gently(old_sha1, 0);
 		new_cmit = lookup_commit_reference_gently(b->sha1, 0);
 		if (!old_cmit || !new_cmit) {
-			unlock_ref(lock);
 			return error("Branch %s is missing commits.", b->name);
 		}
 
 		if (!in_merge_bases(old_cmit, new_cmit)) {
-			unlock_ref(lock);
 			warning("Not updating %s"
 				" (new tip %s does not contain %s)",
 				b->name, sha1_to_hex(b->sha1), sha1_to_hex(old_sha1));
 			return -1;
 		}
 	}
-	if (write_ref_sha1(lock, b->sha1, msg) < 0)
-		return error("Unable to update %s", b->name);
+	transaction = ref_transaction_begin();
+	if ((!transaction ||
+	    ref_transaction_update(transaction, b->name, b->sha1, old_sha1,
+				   0, 1)) ||
+	    (ref_transaction_commit(transaction, msg, &err) &&
+	     !(transaction = NULL))) {
+		ref_transaction_rollback(transaction);
+		error("Unable to update branch %s: %s", b->name, err.buf);
+		strbuf_release(&err);
+		return -1;
+	}
 	return 0;
 }
 
-- 
1.9.1.532.gf8485a6

[PATCH v5 16/30] branch.c: use ref transaction for all ref updates

[Ronnie Sahlberg]

Change create_branch to use a ref transaction when creating the new branch.
ref_transaction_create will check that the ref does not already exist and fail
otherwise meaning that we no longer need to keep a lock on the ref during the
setup_tracking. This simplifies the code since we can now do the transaction
in one single step.

If the forcing flag is false then use ref_transaction_create since this will
fail if the ref already exist. Otherwise use ref_transaction_update.

This also fixes a race condition in the old code where two concurrent
create_branch could race since the lock_any_ref_for_update/write_ref_sha1
did not protect against the ref already existsing. I.e. one thread could end up
overwriting a branch even if the forcing flag is false.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 branch.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/branch.c b/branch.c
index 660097b..2aa5c82 100644
--- a/branch.c
+++ b/branch.c
@@ -226,7 +226,6 @@ void create_branch(const char *head,
 		   int force, int reflog, int clobber_head,
 		   int quiet, enum branch_track track)
 {
-	struct ref_lock *lock = NULL;
 	struct commit *commit;
 	unsigned char sha1[20];
 	char *real_ref, msg[PATH_MAX + 20];
@@ -285,15 +284,6 @@ void create_branch(const char *head,
 		die(_("Not a valid branch point: '%s'."), start_name);
 	hashcpy(sha1, commit->object.sha1);
 
-	if (!dont_change_ref) {
-		lock = lock_any_ref_for_update(ref.buf, NULL, 0, NULL);
-		if (!lock)
-			die_errno(_("Failed to lock ref for update"));
-	}
-
-	if (reflog)
-		log_all_ref_updates = 1;
-
 	if (forcing)
 		snprintf(msg, sizeof msg, "branch: Reset to %s",
 			 start_name);
@@ -301,13 +291,25 @@ void create_branch(const char *head,
 		snprintf(msg, sizeof msg, "branch: Created from %s",
 			 start_name);
 
+	if (reflog)
+		log_all_ref_updates = 1;
+
+	if (!dont_change_ref) {
+		struct ref_transaction *transaction;
+		struct strbuf err = STRBUF_INIT;
+
+		transaction = ref_transaction_begin();
+		if (!transaction ||
+			ref_transaction_update(transaction, ref.buf, sha1,
+					       null_sha1, 0, !forcing) ||
+			ref_transaction_commit(transaction, msg, &err))
+				die_errno(_("%s: failed to write ref: %s"),
+					  ref.buf, err.buf);
+	}
+
 	if (real_ref && track)
 		setup_tracking(ref.buf + 11, real_ref, track, quiet);
 
-	if (!dont_change_ref)
-		if (write_ref_sha1(lock, sha1, msg) < 0)
-			die_errno(_("Failed to write ref"));
-
 	strbuf_release(&ref);
 	free(real_ref);
 }
-- 
1.9.1.532.gf8485a6

[PATCH v5 17/30] refs.c: change update_ref to use a transaction

[Ronnie Sahlberg]

Change the update_ref helper function to use a ref transaction internally.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 refs.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/refs.c b/refs.c
index 0a4e28e..563f336 100644
--- a/refs.c
+++ b/refs.c
@@ -3396,11 +3396,28 @@ int update_ref(const char *action, const char *refname,
 	       const unsigned char *sha1, const unsigned char *oldval,
 	       int flags, enum action_on_err onerr)
 {
-	struct ref_lock *lock;
-	lock = update_ref_lock(refname, oldval, flags, NULL, onerr);
-	if (!lock)
+	struct ref_transaction *t;
+	struct strbuf err = STRBUF_INIT;
+
+	t = ref_transaction_begin();
+	if ((!t ||
+	    ref_transaction_update(t, refname, sha1, oldval, flags,
+				   !!oldval)) ||
+	    (ref_transaction_commit(t, action, &err) && !(t = NULL))) {
+		const char *str = "update_ref failed for ref '%s': %s";
+
+		ref_transaction_rollback(t);
+		switch (onerr) {
+		case UPDATE_REFS_MSG_ON_ERR:
+			error(str, refname, err.buf); break;
+		case UPDATE_REFS_DIE_ON_ERR:
+			die(str, refname, err.buf); break;
+		case UPDATE_REFS_QUIET_ON_ERR: break;
+		}
+		strbuf_release(&err);
 		return 1;
-	return update_ref_write(action, refname, sha1, lock, NULL, onerr);
+	}
+	return 0;
 }
 
 static int ref_update_compare(const void *r1, const void *r2)
-- 
1.9.1.532.gf8485a6

[PATCH v5 18/30] refs.c: free the transaction before returning when number of updates is 0

[Ronnie Sahlberg]

We have to free the transaction before returning in the early check for
'return early if number of updates == 0' or else the following code would
create a memory leak with the transaction never being freed :
   t = ref_transaction_begin()
   ref_transaction_commit(t)

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 refs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/refs.c b/refs.c
index 563f336..c6ee43c 100644
--- a/refs.c
+++ b/refs.c
@@ -3451,8 +3451,10 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 	int n = transaction->nr;
 	struct ref_update **updates = transaction->updates;
 
-	if (!n)
+	if (!n) {
+		ref_transaction_free(transaction);
 		return 0;
+	}
 
 	/* Allocate work space */
 	delnames = xmalloc(sizeof(*delnames) * n);
-- 
1.9.1.532.gf8485a6

[PATCH v5 19/30] refs.c: ref_transaction_commit should not free the transaction

[Ronnie Sahlberg]

Change ref_transaction_commit so that it does not free the transaction.
Instead require that a caller will end a transaction by either calling
ref_transaction_rollback or ref_transaction_free.

By having the transaction object remaining valid after _commit returns allows
us to write much nicer code and still be able to call ref_transaction_rollback
safely. Instead of this horribleness
	t = ref_transaction_begin();
	if ((!t ||
	    ref_transaction_update(t, refname, sha1, oldval, flags,
				   !!oldval)) ||
	    (ref_transaction_commit(t, action, &err) && !(t = NULL))) {
		ref_transaction_rollback(t);

we can now just do the much nicer
	t = ref_transaction_begin();
	if (!t ||
	    ref_transaction_update(t, refname, sha1, oldval, flags,
				   !!oldval) ||
	    ref_transaction_commit(&t, action, &err)) {
		ref_transaction_rollback(t);
		... die/return ...

	ref_transaction_free(transaction);

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 branch.c             |  1 +
 builtin/commit.c     |  1 +
 builtin/replace.c    |  1 +
 builtin/tag.c        |  1 +
 builtin/update-ref.c |  1 +
 fast-import.c        |  8 ++++----
 refs.c               | 14 ++++++--------
 refs.h               | 14 +++++++++-----
 sequencer.c          |  8 ++++----
 9 files changed, 28 insertions(+), 21 deletions(-)

diff --git a/branch.c b/branch.c
index 2aa5c82..8e58908 100644
--- a/branch.c
+++ b/branch.c
@@ -305,6 +305,7 @@ void create_branch(const char *head,
 			ref_transaction_commit(transaction, msg, &err))
 				die_errno(_("%s: failed to write ref: %s"),
 					  ref.buf, err.buf);
+		ref_transaction_free(transaction);
 	}
 
 	if (real_ref && track)
diff --git a/builtin/commit.c b/builtin/commit.c
index a56f47a..b806c59 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -1686,6 +1686,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		rollback_index_files();
 		die(_("HEAD: cannot update ref: %s"), err.buf);
 	}
+	ref_transaction_free(transaction);
 
 	unlink(git_path("CHERRY_PICK_HEAD"));
 	unlink(git_path("REVERT_HEAD"));
diff --git a/builtin/replace.c b/builtin/replace.c
index b037b29..5999f7d 100644
--- a/builtin/replace.c
+++ b/builtin/replace.c
@@ -165,6 +165,7 @@ static int replace_object(const char *object_ref, const char *replace_ref,
 	    ref_transaction_commit(transaction, NULL, &err))
 		die(_("%s: failed to replace ref: %s"), ref, err.buf);
 
+	ref_transaction_free(transaction);
 	return 0;
 }
 
diff --git a/builtin/tag.c b/builtin/tag.c
index 31e32cb..4701bda 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -648,6 +648,7 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 				   0, !is_null_sha1(prev)) ||
 	    ref_transaction_commit(transaction, NULL, &err))
 		die(_("%s: cannot update the ref: %s"), ref.buf, err.buf);
+	ref_transaction_free(transaction);
 	if (force && !is_null_sha1(prev) && hashcmp(prev, object))
 		printf(_("Updated tag '%s' (was %s)\n"), tag, find_unique_abbrev(prev, DEFAULT_ABBREV));
 
diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index fc3512f..7fe9c11 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -373,6 +373,7 @@ int cmd_update_ref(int argc, const char **argv, const char *prefix)
 		update_refs_stdin();
 		if (ref_transaction_commit(transaction, msg, &err))
 			die("%s", err.buf);
+		ref_transaction_free(transaction);
 		return 0;
 	}
 
diff --git a/fast-import.c b/fast-import.c
index 35de36a..b3c6a04 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -1703,16 +1703,16 @@ static int update_branch(struct branch *b)
 		}
 	}
 	transaction = ref_transaction_begin();
-	if ((!transaction ||
+	if (!transaction ||
 	    ref_transaction_update(transaction, b->name, b->sha1, old_sha1,
-				   0, 1)) ||
-	    (ref_transaction_commit(transaction, msg, &err) &&
-	     !(transaction = NULL))) {
+				   0, 1) ||
+	    ref_transaction_commit(transaction, msg, &err)) {
 		ref_transaction_rollback(transaction);
 		error("Unable to update branch %s: %s", b->name, err.buf);
 		strbuf_release(&err);
 		return -1;
 	}
+	ref_transaction_free(transaction);
 	return 0;
 }
 
diff --git a/refs.c b/refs.c
index c6ee43c..fcbdf9b 100644
--- a/refs.c
+++ b/refs.c
@@ -3302,7 +3302,7 @@ struct ref_transaction *ref_transaction_begin(void)
 	return xcalloc(1, sizeof(struct ref_transaction));
 }
 
-static void ref_transaction_free(struct ref_transaction *transaction)
+void ref_transaction_free(struct ref_transaction *transaction)
 {
 	int i;
 
@@ -3400,10 +3400,10 @@ int update_ref(const char *action, const char *refname,
 	struct strbuf err = STRBUF_INIT;
 
 	t = ref_transaction_begin();
-	if ((!t ||
+	if (!t ||
 	    ref_transaction_update(t, refname, sha1, oldval, flags,
-				   !!oldval)) ||
-	    (ref_transaction_commit(t, action, &err) && !(t = NULL))) {
+				   !!oldval) ||
+	    ref_transaction_commit(t, action, &err)) {
 		const char *str = "update_ref failed for ref '%s': %s";
 
 		ref_transaction_rollback(t);
@@ -3417,6 +3417,7 @@ int update_ref(const char *action, const char *refname,
 		strbuf_release(&err);
 		return 1;
 	}
+	ref_transaction_free(t);
 	return 0;
 }
 
@@ -3451,10 +3452,8 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 	int n = transaction->nr;
 	struct ref_update **updates = transaction->updates;
 
-	if (!n) {
-		ref_transaction_free(transaction);
+	if (!n)
 		return 0;
-	}
 
 	/* Allocate work space */
 	delnames = xmalloc(sizeof(*delnames) * n);
@@ -3520,7 +3519,6 @@ cleanup:
 		if (updates[i]->lock)
 			unlock_ref(updates[i]->lock);
 	free(delnames);
-	ref_transaction_free(transaction);
 	return ret;
 }
 
diff --git a/refs.h b/refs.h
index 5eb500e..fcde43e 100644
--- a/refs.h
+++ b/refs.h
@@ -210,8 +210,8 @@ enum action_on_err {
 
 /*
  * Begin a reference transaction.  The reference transaction must
- * eventually be commited using ref_transaction_commit() or rolled
- * back using ref_transaction_rollback().
+ * eventually be freed by either calling ref_transaction_rollback()
+ * or ref_transaction_free().
  */
 struct ref_transaction *ref_transaction_begin(void);
 
@@ -267,13 +267,17 @@ int ref_transaction_delete(struct ref_transaction *transaction,
 /*
  * Commit all of the changes that have been queued in transaction, as
  * atomically as possible.  Return a nonzero value if there is a
- * problem.  The ref_transaction is freed by this function.
- * If err is non-NULL we will add an error string to it to explain why
- * the transaction failed.
+ * problem. If err is non-NULL we will add an error string to it to explain
+ * why the transaction failed.
  */
 int ref_transaction_commit(struct ref_transaction *transaction,
 			   const char *msg, struct strbuf *err);
 
+/*
+ * Free an existing transaction.
+ */
+void ref_transaction_free(struct ref_transaction *transaction);
+
 /** Lock a ref and then write its file */
 int update_ref(const char *action, const char *refname,
 		const unsigned char *sha1, const unsigned char *oldval,
diff --git a/sequencer.c b/sequencer.c
index 9282a12..0cfdaf0 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -283,17 +283,17 @@ static int fast_forward_to(const unsigned char *to, const unsigned char *from,
 	strbuf_addf(&sb, "%s: fast-forward", action_name(opts));
 
 	transaction = ref_transaction_begin();
-	if ((!transaction ||
+	if (!transaction ||
 	    ref_transaction_update(transaction, "HEAD", to, from,
-				   0, !unborn)) ||
-	    (ref_transaction_commit(transaction, sb.buf, &err) &&
-	     !(transaction = NULL))) {
+				   0, !unborn) ||
+	    ref_transaction_commit(transaction, sb.buf, &err)) {
 		ref_transaction_rollback(transaction);
 		error(_("HEAD: Could not fast-forward: %s\n"), err.buf);
 		strbuf_release(&sb);
 		strbuf_release(&err);
 		return -1;
 	}
+	ref_transaction_free(transaction);
 
 	strbuf_release(&sb);
 	return 0;
-- 
1.9.1.532.gf8485a6

[PATCH v5 20/30] fetch.c: clear errno before calling functions that might set it

[Ronnie Sahlberg]

In s_update_ref there are two calls that when they fail we return an error
based on the errno value. In particular we want to return a specific error
if ENOTDIR happened. Both these functions do have failure modes where they
may return an error without updating errno, in which case a previous and
unrelated ENOTDIT may cause us to return the wrong error. Clear errno before
calling any functions if we check errno afterwards.

Also skip initializing a static variable to 0. Statics live in .bss and
are all automatically initialized to 0.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 builtin/fetch.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index 55f457c..a93c893 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -44,7 +44,7 @@ static struct transport *gtransport;
 static struct transport *gsecondary;
 static const char *submodule_prefix = "";
 static const char *recurse_submodules_default;
-static int shown_url = 0;
+static int shown_url;
 
 static int option_parse_recurse_submodules(const struct option *opt,
 				   const char *arg, int unset)
@@ -382,6 +382,8 @@ static int s_update_ref(const char *action,
 	if (!rla)
 		rla = default_rla.buf;
 	snprintf(msg, sizeof(msg), "%s: %s", rla, action);
+
+	errno = 0;
 	lock = lock_any_ref_for_update(ref->name,
 				       check_old ? ref->old_sha1 : NULL,
 				       0, NULL);
-- 
1.9.1.532.gf8485a6

[PATCH v5 21/30] fetch.c: change s_update_ref to use a ref transaction

[Ronnie Sahlberg]

Change s_update_ref to use a ref transaction for the ref update.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 builtin/fetch.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index a93c893..b41d7b7 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -375,7 +375,7 @@ static int s_update_ref(const char *action,
 {
 	char msg[1024];
 	char *rla = getenv("GIT_REFLOG_ACTION");
-	static struct ref_lock *lock;
+	struct ref_transaction *transaction;
 
 	if (dry_run)
 		return 0;
@@ -384,15 +384,16 @@ static int s_update_ref(const char *action,
 	snprintf(msg, sizeof(msg), "%s: %s", rla, action);
 
 	errno = 0;
-	lock = lock_any_ref_for_update(ref->name,
-				       check_old ? ref->old_sha1 : NULL,
-				       0, NULL);
-	if (!lock)
-		return errno == ENOTDIR ? STORE_REF_ERROR_DF_CONFLICT :
-					  STORE_REF_ERROR_OTHER;
-	if (write_ref_sha1(lock, ref->new_sha1, msg) < 0)
+	transaction = ref_transaction_begin();
+	if (!transaction ||
+	    ref_transaction_update(transaction, ref->name, ref->new_sha1,
+				   ref->old_sha1, 0, check_old) ||
+	    ref_transaction_commit(transaction, msg, NULL)) {
+		ref_transaction_rollback(transaction);
 		return errno == ENOTDIR ? STORE_REF_ERROR_DF_CONFLICT :
 					  STORE_REF_ERROR_OTHER;
+	}
+	ref_transaction_free(transaction);
 	return 0;
 }
 
-- 
1.9.1.532.gf8485a6

[PATCH v5 22/30] fetch.c: use a single ref transaction for all ref updates

[Ronnie Sahlberg]

Change store_updated_refs to use a single ref transaction for all refs that
are updated during the fetch. This makes the fetch more atomic when update
failures occur.

Since ref update failures will now no longer occur in the code path for
updating a single ref in s_update_ref, we no longer have as detailed error
message logging the exact reference and the ref log action as in the old cod
Instead since we fail the entire transaction we log a much more generic
message. But since we commit the transaction using MSG_ON_ERR we will log
an error containing the ref name if either locking of writing the ref would
so the regression in the log message is minor.

This will also change the order in which errors are checked for and logged
which may alter which error will be logged if there are multiple errors
occuring during a fetch.

For example, assume we have a fetch for two refs that both would fail.
Where the first ref would fail with ENOTDIR due to a directory in the ref
path not existing, and the second ref in the fetch would fail due to
the check in update_logical_ref():
        if (current_branch &&
            !strcmp(ref->name, current_branch->name) &&
            !(update_head_ok || is_bare_repository()) &&
            !is_null_sha1(ref->old_sha1)) {
                /*
                 * If this is the head, and it's not okay to update
                 * the head, and the old value of the head isn't empty...
                 */

In the old code since we would update the refs one ref at a time we would
first fail the ENOTDIR and then fail the second update of HEAD as well.
But since the first ref failed with ENOTDIR we would eventually fail the who
fetch with STORE_REF_ERROR_DF_CONFLICT

In the new code, since we defer committing the transaction until all refs
have been processed, we would now detect that the second ref was bad and
rollback the transaction before we would even try start writing the update t
disk and thus we would not return STORE_REF_ERROR_DF_CONFLICT for this case.

I think this new behaviour is more correct, since if there was a problem
we would not even try to commit the transaction but need to highlight this
change in how/what errors are reported.
This change in what error is returned only occurs if there are multiple
refs that fail to update and only some, but not all, of them fail due to
ENOTDIR.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 builtin/fetch.c | 34 ++++++++++++++++------------------
 1 file changed, 16 insertions(+), 18 deletions(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index b41d7b7..5dbd0f0 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -45,6 +45,7 @@ static struct transport *gsecondary;
 static const char *submodule_prefix = "";
 static const char *recurse_submodules_default;
 static int shown_url;
+struct ref_transaction *transaction;
 
 static int option_parse_recurse_submodules(const struct option *opt,
 				   const char *arg, int unset)
@@ -373,27 +374,13 @@ static int s_update_ref(const char *action,
 			struct ref *ref,
 			int check_old)
 {
-	char msg[1024];
-	char *rla = getenv("GIT_REFLOG_ACTION");
-	struct ref_transaction *transaction;
-
 	if (dry_run)
 		return 0;
-	if (!rla)
-		rla = default_rla.buf;
-	snprintf(msg, sizeof(msg), "%s: %s", rla, action);
 
-	errno = 0;
-	transaction = ref_transaction_begin();
-	if (!transaction ||
-	    ref_transaction_update(transaction, ref->name, ref->new_sha1,
-				   ref->old_sha1, 0, check_old) ||
-	    ref_transaction_commit(transaction, msg, NULL)) {
-		ref_transaction_rollback(transaction);
-		return errno == ENOTDIR ? STORE_REF_ERROR_DF_CONFLICT :
-					  STORE_REF_ERROR_OTHER;
-	}
-	ref_transaction_free(transaction);
+	if (ref_transaction_update(transaction, ref->name, ref->new_sha1,
+			       ref->old_sha1, 0, check_old))
+		return STORE_REF_ERROR_OTHER;
+
 	return 0;
 }
 
@@ -565,6 +552,13 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
 		goto abort;
 	}
 
+	errno = 0;
+	transaction = ref_transaction_begin();
+	if (!transaction) {
+		rc = error(_("cannot start ref transaction\n"));
+		goto abort;
+	}
+
 	/*
 	 * We do a pass for each fetch_head_status type in their enum order, so
 	 * merged entries are written before not-for-merge. That lets readers
@@ -676,6 +670,10 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
 			}
 		}
 	}
+	if (ref_transaction_commit(transaction, "fetch_ref transaction", NULL))
+		rc |= errno == ENOTDIR ? STORE_REF_ERROR_DF_CONFLICT :
+		  STORE_REF_ERROR_OTHER;
+	ref_transaction_free(transaction);
 
 	if (rc & STORE_REF_ERROR_DF_CONFLICT)
 		error(_("some local refs could not be updated; try running\n"
-- 
1.9.1.532.gf8485a6

[PATCH v5 23/30] receive-pack.c: use a reference transaction for updating the refs

[Ronnie Sahlberg]

Wrap all the ref updates inside a transaction to make the update atomic.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 builtin/receive-pack.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index c323081..d580176 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -46,6 +46,8 @@ static void *head_name_to_free;
 static int sent_capabilities;
 static int shallow_update;
 static const char *alt_shallow_file;
+struct strbuf err = STRBUF_INIT;
+struct ref_transaction *transaction;
 
 static enum deny_action parse_deny_action(const char *var, const char *value)
 {
@@ -475,7 +477,6 @@ static const char *update(struct command *cmd, struct shallow_info *si)
 	const char *namespaced_name;
 	unsigned char *old_sha1 = cmd->old_sha1;
 	unsigned char *new_sha1 = cmd->new_sha1;
-	struct ref_lock *lock;
 
 	/* only refs/... are allowed */
 	if (!starts_with(name, "refs/") || check_refname_format(name + 5, 0)) {
@@ -580,15 +581,9 @@ static const char *update(struct command *cmd, struct shallow_info *si)
 		    update_shallow_ref(cmd, si))
 			return "shallow error";
 
-		lock = lock_any_ref_for_update(namespaced_name, old_sha1,
-					       0, NULL);
-		if (!lock) {
-			rp_error("failed to lock %s", name);
-			return "failed to lock";
-		}
-		if (write_ref_sha1(lock, new_sha1, "push")) {
-			return "failed to write"; /* error() already called */
-		}
+		if (ref_transaction_update(transaction, namespaced_name,
+					   new_sha1, old_sha1, 0, 1))
+			return "failed to update";
 		return NULL; /* good */
 	}
 }
@@ -812,6 +807,7 @@ static void execute_commands(struct command *commands,
 	head_name = head_name_to_free = resolve_refdup("HEAD", sha1, 0, NULL);
 
 	checked_connectivity = 1;
+	transaction = ref_transaction_begin();
 	for (cmd = commands; cmd; cmd = cmd->next) {
 		if (cmd->error_string)
 			continue;
@@ -827,6 +823,10 @@ static void execute_commands(struct command *commands,
 			checked_connectivity = 0;
 		}
 	}
+	if (ref_transaction_commit(transaction, "push", &err))
+		error("%s", err.buf);
+	ref_transaction_free(transaction);
+	strbuf_release(&err);
 
 	if (shallow_update && !checked_connectivity)
 		error("BUG: run 'git fsck' for safety.\n"
-- 
1.9.1.532.gf8485a6

[PATCH v5 24/30] fast-import.c: use a ref transaction when dumping tags

[Ronnie Sahlberg]

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 fast-import.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/fast-import.c b/fast-import.c
index b3c6a04..bd73a6d 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -1731,15 +1731,22 @@ static void dump_tags(void)
 {
 	static const char *msg = "fast-import";
 	struct tag *t;
-	struct ref_lock *lock;
 	char ref_name[PATH_MAX];
+	struct strbuf err = STRBUF_INIT;
+	struct ref_transaction *transaction;
 
+	transaction = ref_transaction_begin();
 	for (t = first_tag; t; t = t->next_tag) {
-		sprintf(ref_name, "tags/%s", t->name);
-		lock = lock_ref_sha1(ref_name, NULL);
-		if (!lock || write_ref_sha1(lock, t->sha1, msg) < 0)
-			failure |= error("Unable to update %s", ref_name);
+		sprintf(ref_name, "refs/tags/%s", t->name);
+
+		if (ref_transaction_update(transaction, ref_name, t->sha1,
+					   NULL, 0, 0))
+			failure |= error("Unable to update %s", err.buf);
 	}
+	if (failure || ref_transaction_commit(transaction, msg, &err))
+		failure |= error("Unable to update %s", err.buf);
+	ref_transaction_free(transaction);
+	strbuf_release(&err);
 }
 
 static void dump_marks_helper(FILE *f,
-- 
1.9.1.532.gf8485a6

[PATCH v5 25/30] walker.c: use ref transaction for ref updates

[Ronnie Sahlberg]

Switch to using ref transactions in walker_fetch(). As part of the refactoring
to use ref transactions we also fix a potential memory leak where in the
original code if write_ref_sha1() would fail we would end up returning from
the function without free()ing the msg string.

This changes the locking slightly for walker_fetch. Previously the code would
lock all refs before writing them but now we do not lock the refs until the
commit stage. There is thus a very short window where changes could be done
locally during the fetch which would be overwritten when the fetch completes
and commits its transaction. But this window should be reasonably short.
Even if this race does trigger, since both the old code and the new code
just overwrites the refs to the new values without checking or comparing
them with the previous value, this is not too dissimilar to a similar scenario
where you first do a ref change locally and then later do a fetch that
overwrites the local change. With this in mind I do not see the change in
locking semantics to be critical.

Note that this function is only called when fetching from a remote HTTP
repository onto the local (most of the time single-user) repository which
likely means that the type of collissions that the previous locking would
protect against and cause the fetch to fail for to be even more rare.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 walker.c | 51 ++++++++++++++++++++++++++-------------------------
 1 file changed, 26 insertions(+), 25 deletions(-)

diff --git a/walker.c b/walker.c
index 1dd86b8..6044ccf 100644
--- a/walker.c
+++ b/walker.c
@@ -251,24 +251,18 @@ void walker_targets_free(int targets, char **target, const char **write_ref)
 int walker_fetch(struct walker *walker, int targets, char **target,
 		 const char **write_ref, const char *write_ref_log_details)
 {
-	struct ref_lock **lock = xcalloc(targets, sizeof(struct ref_lock *));
+	char ref_name[PATH_MAX];
+	struct strbuf err = STRBUF_INIT;
+	struct ref_transaction *transaction;
 	unsigned char *sha1 = xmalloc(targets * 20);
-	char *msg;
-	int ret;
+	char *msg = NULL;
 	int i;
 
 	save_commit_buffer = 0;
 
-	for (i = 0; i < targets; i++) {
-		if (!write_ref || !write_ref[i])
-			continue;
-
-		lock[i] = lock_ref_sha1(write_ref[i], NULL);
-		if (!lock[i]) {
-			error("Can't lock ref %s", write_ref[i]);
-			goto unlock_and_fail;
-		}
-	}
+	transaction = ref_transaction_begin();
+	if (!transaction)
+		return -1;
 
 	if (!walker->get_recover)
 		for_each_ref(mark_complete, NULL);
@@ -276,14 +270,14 @@ int walker_fetch(struct walker *walker, int targets, char **target,
 	for (i = 0; i < targets; i++) {
 		if (interpret_target(walker, target[i], &sha1[20 * i])) {
 			error("Could not interpret response from server '%s' as something to pull", target[i]);
-			goto unlock_and_fail;
+			goto rollback_and_fail;
 		}
 		if (process(walker, lookup_unknown_object(&sha1[20 * i])))
-			goto unlock_and_fail;
+			goto rollback_and_fail;
 	}
 
 	if (loop(walker))
-		goto unlock_and_fail;
+		goto rollback_and_fail;
 
 	if (write_ref_log_details) {
 		msg = xmalloc(strlen(write_ref_log_details) + 12);
@@ -294,19 +288,26 @@ int walker_fetch(struct walker *walker, int targets, char **target,
 	for (i = 0; i < targets; i++) {
 		if (!write_ref || !write_ref[i])
 			continue;
-		ret = write_ref_sha1(lock[i], &sha1[20 * i], msg ? msg : "fetch (unknown)");
-		lock[i] = NULL;
-		if (ret)
-			goto unlock_and_fail;
+		sprintf(ref_name, "refs/%s", write_ref[i]);
+		if (ref_transaction_update(transaction, ref_name,
+					   &sha1[20 * i], NULL,
+					   0, 0))
+			goto rollback_and_fail;
+	}
+
+	if (ref_transaction_commit(transaction, msg ? msg : "fetch (unknown)",
+				   &err)) {
+		error("%s", err.buf);
+		goto rollback_and_fail;
 	}
-	free(msg);
 
+	free(msg);
 	return 0;
 
-unlock_and_fail:
-	for (i = 0; i < targets; i++)
-		if (lock[i])
-			unlock_ref(lock[i]);
+rollback_and_fail:
+	free(msg);
+	strbuf_release(&err);
+	ref_transaction_free(transaction);
 
 	return -1;
 }
-- 
1.9.1.532.gf8485a6

[PATCH v5 26/30] refs.c: make write_ref_sha1 static

[Ronnie Sahlberg]

No external users call write_ref_sha1 any more so lets declare it static.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 refs.c | 4 +++-
 refs.h | 3 ---
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/refs.c b/refs.c
index fcbdf9b..020eadf 100644
--- a/refs.c
+++ b/refs.c
@@ -251,6 +251,8 @@ struct ref_entry {
 };
 
 static void read_loose_refs(const char *dirname, struct ref_dir *dir);
+static int write_ref_sha1(struct ref_lock *lock,
+			  const unsigned char *sha1, const char *logmsg);
 
 static struct ref_dir *get_ref_dir(struct ref_entry *entry)
 {
@@ -2798,7 +2800,7 @@ static int is_branch(const char *refname)
 	return !strcmp(refname, "HEAD") || starts_with(refname, "refs/heads/");
 }
 
-int write_ref_sha1(struct ref_lock *lock,
+static int write_ref_sha1(struct ref_lock *lock,
 	const unsigned char *sha1, const char *logmsg)
 {
 	static char term = '\n';
diff --git a/refs.h b/refs.h
index fcde43e..bc8a95b 100644
--- a/refs.h
+++ b/refs.h
@@ -150,9 +150,6 @@ extern int commit_ref(struct ref_lock *lock);
 /** Release any lock taken but not written. **/
 extern void unlock_ref(struct ref_lock *lock);
 
-/** Writes sha1 into the ref specified by the lock. **/
-extern int write_ref_sha1(struct ref_lock *lock, const unsigned char *sha1, const char *msg);
-
 /** Setup reflog before using. **/
 int log_ref_setup(const char *refname, char *logfile, int bufsize);
 
-- 
1.9.1.532.gf8485a6

[PATCH v5 27/30] refs.c: make lock_ref_sha1 static

[Ronnie Sahlberg]

No external callers reference lock_ref_sha1 any more so lets declare it static.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 refs.c | 2 +-
 refs.h | 3 ---
 2 files changed, 1 insertion(+), 4 deletions(-)

diff --git a/refs.c b/refs.c
index 020eadf..a82d6ba 100644
--- a/refs.c
+++ b/refs.c
@@ -2130,7 +2130,7 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 	return NULL;
 }
 
-struct ref_lock *lock_ref_sha1(const char *refname, const unsigned char *old_sha1)
+static struct ref_lock *lock_ref_sha1(const char *refname, const unsigned char *old_sha1)
 {
 	char refpath[PATH_MAX];
 	if (check_refname_format(refname, 0))
diff --git a/refs.h b/refs.h
index bc8a95b..b14fe86 100644
--- a/refs.h
+++ b/refs.h
@@ -132,9 +132,6 @@ extern int ref_exists(const char *);
  */
 extern int peel_ref(const char *refname, unsigned char *sha1);
 
-/** Locks a "refs/" ref returning the lock on success and NULL on failure. **/
-extern struct ref_lock *lock_ref_sha1(const char *refname, const unsigned char *old_sha1);
-
 /** Locks any ref (for 'HEAD' type refs). */
 #define REF_NODEREF	0x01
 extern struct ref_lock *lock_any_ref_for_update(const char *refname,
-- 
1.9.1.532.gf8485a6

[PATCH v5 28/30] refs.c: add transaction.status and track OPEN/CLOSED/ERROR

[Ronnie Sahlberg]

Track the status of a transaction in a new status field. Check the field for
sanity, i.e. that status must be OPEN when _commit/_create/_delete or
_update is called or else die(BUG:...)

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 refs.c | 37 +++++++++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/refs.c b/refs.c
index a82d6ba..206e1a2 100644
--- a/refs.c
+++ b/refs.c
@@ -3288,6 +3288,12 @@ struct ref_update {
 	const char refname[FLEX_ARRAY];
 };
 
+enum ref_transaction_status {
+	REF_TRANSACTION_OPEN   = 0,
+	REF_TRANSACTION_CLOSED = 1,
+	REF_TRANSACTION_ERROR  = 2,
+};
+
 /*
  * Data structure for holding a reference transaction, which can
  * consist of checks and updates to multiple references, carried out
@@ -3297,6 +3303,7 @@ struct ref_transaction {
 	struct ref_update **updates;
 	size_t alloc;
 	size_t nr;
+	enum ref_transaction_status status;
 };
 
 struct ref_transaction *ref_transaction_begin(void)
@@ -3320,6 +3327,11 @@ void ref_transaction_free(struct ref_transaction *transaction)
 
 void ref_transaction_rollback(struct ref_transaction *transaction)
 {
+	if (!transaction)
+		return;
+
+	transaction->status = REF_TRANSACTION_ERROR;
+
 	ref_transaction_free(transaction);
 }
 
@@ -3344,7 +3356,10 @@ int ref_transaction_update(struct ref_transaction *transaction,
 	struct ref_update *update;
 
 	if (have_old && !old_sha1)
-		die("have_old is true but old_sha1 is NULL");
+		die("BUG: have_old is true but old_sha1 is NULL");
+
+	if (transaction->status != REF_TRANSACTION_OPEN)
+		die("BUG: update on transaction that is not open");
 
 	update = add_update(transaction, refname);
 	hashcpy(update->new_sha1, new_sha1);
@@ -3363,7 +3378,10 @@ int ref_transaction_create(struct ref_transaction *transaction,
 	struct ref_update *update;
 
 	if (!new_sha1 || is_null_sha1(new_sha1))
-		die("create ref with null new_sha1");
+		die("BUG: create ref with null new_sha1");
+
+	if (transaction->status != REF_TRANSACTION_OPEN)
+		die("BUG: create on transaction that is not open");
 
 	update = add_update(transaction, refname);
 
@@ -3382,7 +3400,10 @@ int ref_transaction_delete(struct ref_transaction *transaction,
 	struct ref_update *update;
 
 	if (have_old && !old_sha1)
-		die("have_old is true but old_sha1 is NULL");
+		die("BUG: have_old is true but old_sha1 is NULL");
+
+	if (transaction->status != REF_TRANSACTION_OPEN)
+		die("BUG: delete on transaction that is not open");
 
 	update = add_update(transaction, refname);
 	update->flags = flags;
@@ -3454,8 +3475,13 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 	int n = transaction->nr;
 	struct ref_update **updates = transaction->updates;
 
-	if (!n)
+	if (transaction->status != REF_TRANSACTION_OPEN)
+		die("BUG: commit on transaction that is not open");
+
+	if (!n) {
+		transaction->status = REF_TRANSACTION_CLOSED;
 		return 0;
+	}
 
 	/* Allocate work space */
 	delnames = xmalloc(sizeof(*delnames) * n);
@@ -3517,6 +3543,9 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 	clear_loose_ref_cache(&ref_cache);
 
 cleanup:
+	transaction->status = ret ? REF_TRANSACTION_ERROR
+	  : REF_TRANSACTION_CLOSED;
+
 	for (i = 0; i < n; i++)
 		if (updates[i]->lock)
 			unlock_ref(updates[i]->lock);
-- 
1.9.1.532.gf8485a6

[PATCH v5 29/30] refs.c: remove the update_ref_lock function

[Ronnie Sahlberg]

Since we now only call update_ref_lock with onerr==QUIET_ON_ERR we no longer
need this function and can replace it with just calling lock_any_ref_for_update
directly.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 refs.c | 30 ++++++------------------------
 1 file changed, 6 insertions(+), 24 deletions(-)

diff --git a/refs.c b/refs.c
index 206e1a2..9f5435d 100644
--- a/refs.c
+++ b/refs.c
@@ -3235,24 +3235,6 @@ int for_each_reflog(each_ref_fn fn, void *cb_data)
 	return retval;
 }
 
-static struct ref_lock *update_ref_lock(const char *refname,
-					const unsigned char *oldval,
-					int flags, int *type_p,
-					enum action_on_err onerr)
-{
-	struct ref_lock *lock;
-	lock = lock_any_ref_for_update(refname, oldval, flags, type_p);
-	if (!lock) {
-		const char *str = "Cannot lock the ref '%s'.";
-		switch (onerr) {
-		case UPDATE_REFS_MSG_ON_ERR: error(str, refname); break;
-		case UPDATE_REFS_DIE_ON_ERR: die(str, refname); break;
-		case UPDATE_REFS_QUIET_ON_ERR: break;
-		}
-	}
-	return lock;
-}
-
 static int update_ref_write(const char *action, const char *refname,
 			    const unsigned char *sha1, struct ref_lock *lock,
 			    struct strbuf *err, enum action_on_err onerr)
@@ -3496,12 +3478,12 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 	for (i = 0; i < n; i++) {
 		struct ref_update *update = updates[i];
 
-		update->lock = update_ref_lock(update->refname,
-					       (update->have_old ?
-						update->old_sha1 : NULL),
-					       update->flags,
-					       &update->type,
-					       UPDATE_REFS_QUIET_ON_ERR);
+		update->lock = lock_any_ref_for_update(update->refname,
+						       (update->have_old ?
+							update->old_sha1 :
+							NULL),
+						       update->flags,
+						       &update->type);
 		if (!update->lock) {
 			if (err)
 				strbuf_addf(err ,"Cannot lock the ref '%s'.",
-- 
1.9.1.532.gf8485a6

[PATCH v5 30/30] refs.c: remove the update_ref_write function

[Ronnie Sahlberg]

Since we only call update_ref_write from a single place and we only call it
with onerr==QUIET_ON_ERR we can just as well get rid of it and just call
write_ref_sha1 directly.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 refs.c | 35 +++++++++--------------------------
 1 file changed, 9 insertions(+), 26 deletions(-)

diff --git a/refs.c b/refs.c
index 9f5435d..875178b 100644
--- a/refs.c
+++ b/refs.c
@@ -3235,25 +3235,6 @@ int for_each_reflog(each_ref_fn fn, void *cb_data)
 	return retval;
 }
 
-static int update_ref_write(const char *action, const char *refname,
-			    const unsigned char *sha1, struct ref_lock *lock,
-			    struct strbuf *err, enum action_on_err onerr)
-{
-	if (write_ref_sha1(lock, sha1, action) < 0) {
-		const char *str = "Cannot update the ref '%s'.";
-		if (err)
-			strbuf_addf(err, str, refname);
-
-		switch (onerr) {
-		case UPDATE_REFS_MSG_ON_ERR: error(str, refname); break;
-		case UPDATE_REFS_DIE_ON_ERR: die(str, refname); break;
-		case UPDATE_REFS_QUIET_ON_ERR: break;
-		}
-		return 1;
-	}
-	return 0;
-}
-
 /**
  * Information needed for a single ref update.  Set new_sha1 to the
  * new value or to zero to delete the ref.  To check the old value
@@ -3498,14 +3479,16 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 		struct ref_update *update = updates[i];
 
 		if (!is_null_sha1(update->new_sha1)) {
-			ret = update_ref_write(msg,
-					       update->refname,
-					       update->new_sha1,
-					       update->lock, err,
-					       UPDATE_REFS_QUIET_ON_ERR);
-			update->lock = NULL; /* freed by update_ref_write */
-			if (ret)
+			ret = write_ref_sha1(update->lock, update->new_sha1,
+					     msg);
+			update->lock = NULL; /* freed by write_ref_sha1 */
+			if (ret) {
+				const char *str = "Cannot update the ref '%s'.";
+
+				if (err)
+					strbuf_addf(err, str, update->refname);
 				goto cleanup;
+			}
 		}
 	}
 
-- 
1.9.1.532.gf8485a6