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ref_transaction_verify(): new function to check a reference's value

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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 <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Michael Haggerty
2015-02-17 18:00:21 +01:00
committed by Junio C Hamano
parent 60294596ba
commit 1618033401
3 changed files with 67 additions and 21 deletions
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34
refs.h
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@ -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 is 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,
@ -308,6 +313,19 @@ int ref_transaction_delete(struct ref_transaction *transaction,
unsigned int flags, const char *msg,
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,
unsigned int flags,
struct strbuf *err);
/*
* Commit all of the changes that have been queued in transaction, as
* atomically as possible.