If NULL is passed to ref_transaction_update()'s new_sha1 parameter,
then just verify old_sha1 (under lock) without trying to change the
new value of the reference.
Use this functionality to add a new function ref_transaction_verify(),
which checks the current value of the reference under lock but doesn't
change it.
Use ref_transaction_verify() in the implementation of "git update-ref
--stdin"'s "verify" command to avoid the awkward need to "update" the
reference to its existing value.
Signed-off-by: Michael Haggerty <mhag...@alum.mit.edu>
---
builtin/update-ref.c | 7 ++-----
refs.c | 47 +++++++++++++++++++++++++++++++++++++++--------
refs.h | 34 ++++++++++++++++++++++++++--------
3 files changed, 67 insertions(+), 21 deletions(-)
diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 76b8aef..a2eedba 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -282,7 +282,6 @@ static const char *parse_cmd_verify(struct ref_transaction
*transaction,
{
struct strbuf err = STRBUF_INIT;
char *refname;
- unsigned char new_sha1[20];
unsigned char old_sha1[20];
refname = parse_refname(input, &next);
@@ -293,13 +292,11 @@ static const char *parse_cmd_verify(struct
ref_transaction *transaction,
PARSE_SHA1_OLD))
hashclr(old_sha1);
- hashcpy(new_sha1, old_sha1);
-
if (*next != line_termination)
die("verify %s: extra input: %s", refname, next);
- if (ref_transaction_update(transaction, refname, new_sha1, old_sha1,
- update_flags, msg, &err))
+ if (ref_transaction_verify(transaction, refname, old_sha1,
+ update_flags, &err))
die("%s", err.buf);
update_flags = 0;
diff --git a/refs.c b/refs.c
index 85815d7..0da680e 100644
--- a/refs.c
+++ b/refs.c
@@ -47,10 +47,16 @@ static unsigned char refname_disposition[256] = {
#define REF_ISPRUNING 0x04
/*
+ * Used as a flag in ref_update::flags when the reference should be
+ * updated to new_sha1.
+ */
+#define REF_HAVE_NEW 0x08
+
+/*
* Used as a flag in ref_update::flags when old_sha1 should be
* checked.
*/
-#define REF_HAVE_OLD 0x08
+#define REF_HAVE_OLD 0x10
/*
* Try to read one refname component from the front of refname.
@@ -3578,10 +3584,17 @@ int for_each_reflog(each_ref_fn fn, void *cb_data)
* not exist before update.
*/
struct ref_update {
+ /*
+ * If (flags & REF_HAVE_NEW), set the reference to this value:
+ */
unsigned char new_sha1[20];
+ /*
+ * If (flags & REF_HAVE_OLD), check that the reference
+ * previously had this value:
+ */
unsigned char old_sha1[20];
/*
- * One or more of REF_HAVE_OLD, REF_NODEREF,
+ * One or more of REF_HAVE_NEW, REF_HAVE_OLD, REF_NODEREF,
* REF_DELETING, and REF_IS_PRUNING:
*/
int flags;
@@ -3666,7 +3679,7 @@ int ref_transaction_update(struct ref_transaction
*transaction,
if (transaction->state != REF_TRANSACTION_OPEN)
die("BUG: update called for transaction that is not open");
- if (!is_null_sha1(new_sha1) &&
+ if (new_sha1 && !is_null_sha1(new_sha1) &&
check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
strbuf_addf(err, "refusing to update ref with bad name %s",
refname);
@@ -3674,7 +3687,10 @@ int ref_transaction_update(struct ref_transaction
*transaction,
}
update = add_update(transaction, refname);
- hashcpy(update->new_sha1, new_sha1);
+ if (new_sha1) {
+ hashcpy(update->new_sha1, new_sha1);
+ flags |= REF_HAVE_NEW;
+ }
if (old_sha1) {
hashcpy(update->old_sha1, old_sha1);
flags |= REF_HAVE_OLD;
@@ -3710,6 +3726,19 @@ int ref_transaction_delete(struct ref_transaction
*transaction,
flags, msg, err);
}
+int ref_transaction_verify(struct ref_transaction *transaction,
+ const char *refname,
+ const unsigned char *old_sha1,
+ int flags,
+ struct strbuf *err)
+{
+ if (!old_sha1)
+ die("BUG: verify called with old_sha1 set to NULL");
+ return ref_transaction_update(transaction, refname,
+ NULL, old_sha1,
+ flags, NULL, err);
+}
+
int update_ref(const char *action, const char *refname,
const unsigned char *sha1, const unsigned char *oldval,
int flags, enum action_on_err onerr)
@@ -3798,7 +3827,7 @@ int ref_transaction_commit(struct ref_transaction
*transaction,
struct ref_update *update = updates[i];
int flags = update->flags;
- if (is_null_sha1(update->new_sha1))
+ if ((flags & REF_HAVE_NEW) && is_null_sha1(update->new_sha1))
flags |= REF_DELETING;
update->lock = lock_ref_sha1_basic(
update->refname,
@@ -3820,8 +3849,9 @@ int ref_transaction_commit(struct ref_transaction
*transaction,
/* Perform updates first so live commits remain referenced */
for (i = 0; i < n; i++) {
struct ref_update *update = updates[i];
+ int flags = update->flags;
- if (!is_null_sha1(update->new_sha1)) {
+ if ((flags & REF_HAVE_NEW) && !is_null_sha1(update->new_sha1)) {
if (write_ref_sha1(update->lock, update->new_sha1,
update->msg)) {
update->lock = NULL; /* freed by write_ref_sha1
*/
@@ -3837,14 +3867,15 @@ int ref_transaction_commit(struct ref_transaction
*transaction,
/* Perform deletes now that updates are safely completed */
for (i = 0; i < n; i++) {
struct ref_update *update = updates[i];
+ int flags = update->flags;
- if (update->lock) {
+ if ((flags & REF_HAVE_NEW) && is_null_sha1(update->new_sha1)) {
if (delete_ref_loose(update->lock, update->type, err)) {
ret = TRANSACTION_GENERIC_ERROR;
goto cleanup;
}
- if (!(update->flags & REF_ISPRUNING))
+ if (!(flags & REF_ISPRUNING))
string_list_append(&refs_to_delete,
update->lock->ref_name);
}
diff --git a/refs.h b/refs.h
index ee612da..02d6e39 100644
--- a/refs.h
+++ b/refs.h
@@ -263,14 +263,19 @@ struct ref_transaction *ref_transaction_begin(struct
strbuf *err);
*/
/*
- * Add a reference update to transaction. new_sha1 is the value that
- * the reference should have after the update, or null_sha1 if it should
- * be deleted. If old_sha1 is non-NULL, then it the value
- * that the reference should have had before the update, or null_sha1 if
- * it must not have existed beforehand.
- * Function returns 0 on success and non-zero on failure. A failure to update
- * means that the transaction as a whole has failed and will need to be
- * rolled back.
+ * Add a reference update to transaction. new_sha1 is the value that
+ * the reference should have after the update, or null_sha1 if it
+ * should be deleted. If new_sha1 is NULL, then the reference is not
+ * changed at all. old_sha1 is the value that the reference must have
+ * before the update, or null_sha1 if it must not have existed
+ * beforehand. The old value is checked after the lock is taken to
+ * prevent races. If the old value doesn't agree with old_sha1, the
+ * whole transaction fails. If old_sha1 is NULL, then the previous
+ * value is not checked.
+ *
+ * Return 0 on success and non-zero on failure. Any failure in the
+ * transaction means that the transaction as a whole has failed and
+ * will need to be rolled back.
*/
int ref_transaction_update(struct ref_transaction *transaction,
const char *refname,
@@ -309,6 +314,19 @@ int ref_transaction_delete(struct ref_transaction
*transaction,
struct strbuf *err);
/*
+ * Verify, within a transaction, that refname has the value old_sha1,
+ * or, if old_sha1 is null_sha1, then verify that the reference
+ * doesn't exist. old_sha1 must be non-NULL. Function returns 0 on
+ * success and non-zero on failure. A failure to verify means that the
+ * transaction as a whole has failed and will need to be rolled back.
+ */
+int ref_transaction_verify(struct ref_transaction *transaction,
+ const char *refname,
+ const unsigned char *old_sha1,
+ int flags,
+ struct strbuf *err);
+
+/*
* Commit all of the changes that have been queued in transaction, as
* atomically as possible.
*
--
2.1.4
--
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