Subject: Re: [PATCH v3 1/6] refs: extract packed_refs_delete_refs() to allow control of transaction

From: Patrick Steinhardt <[email-masked]>
Date: Mon, 17 Jan 2022 08:36:22 +0100

On Thu, Jan 13, 2022 at 01:43:18PM +0100, Ævar Arnfjörð Bjarmason wrote:
> 
> On Thu, Jan 13 2022, Patrick Steinhardt wrote:
> 
> > [[PGP Signed Part:Undecided]]
> > When deleting loose refs, then we also have to delete the refs in the
> > packed backend. This is done by calling `refs_delete_refs()`, which
> > then uses the packed-backend's logic to delete refs. This doesn't allow
> > us to exercise any control over the reference transaction which is being
> > created in the packed backend, which is required in a subsequent commit.
> >
> > Extract a new function `packed_refs_delete_refs()`, which hosts most of
> > the logic to delete refs except for creating the transaction itself.
> > Like this, we can easily create the transaction in the files backend
> > and thus exert more control over it.
> >
> > Signed-off-by: Patrick Steinhardt <[email-masked]>
> > ---
> >  refs/files-backend.c  | 12 +++++++++---
> >  refs/packed-backend.c | 28 +++++++++++++++++++++-------
> >  refs/packed-backend.h |  7 +++++++
> >  3 files changed, 37 insertions(+), 10 deletions(-)
> >
> > diff --git a/refs/files-backend.c b/refs/files-backend.c
> > index 90b671025a..5795e54020 100644
> > --- a/refs/files-backend.c
> > +++ b/refs/files-backend.c
> > @@ -1249,6 +1249,7 @@ static int files_delete_refs(struct ref_store *ref_store, const char *msg,
> >  {
> >  	struct files_ref_store *refs =
> >  		files_downcast(ref_store, REF_STORE_WRITE, "delete_refs");
> > +	struct ref_transaction *transaction = NULL;
> 
> nit: "NULL initialization never needed?
> (re: https://lore.kernel.org/git/[email-masked]/)

It is needed: if locking the packed-refs file fails we `goto error;` and
try to free the transaction without it having been initialized yet.

> >  	struct strbuf err = STRBUF_INIT;
> >  	int i, result = 0;
> >  
> > @@ -1258,10 +1259,14 @@ static int files_delete_refs(struct ref_store *ref_store, const char *msg,
> >  	if (packed_refs_lock(refs->packed_ref_store, 0, &err))
> >  		goto error;
> >  
> > -	if (refs_delete_refs(refs->packed_ref_store, msg, refnames, flags)) {
> > -		packed_refs_unlock(refs->packed_ref_store);
> > +	transaction = ref_store_transaction_begin(refs->packed_ref_store, &err);
> > +	if (!transaction)
> > +		goto error;
> > +
> > +	result = packed_refs_delete_refs(refs->packed_ref_store,
> > +					 transaction, msg, refnames, flags);
> > +	if (result)
> >  		goto error;
> > -	}
> >  
> >  	packed_refs_unlock(refs->packed_ref_store);
> >  
> > @@ -1288,6 +1293,7 @@ static int files_delete_refs(struct ref_store *ref_store, const char *msg,
> >  	else
> >  		error(_("could not delete references: %s"), err.buf);
> >  
> > +	ref_transaction_free(transaction);
> >  	strbuf_release(&err);
> >  	return -1;
> >  }
> > diff --git a/refs/packed-backend.c b/refs/packed-backend.c
> > index 67152c664e..e97d67f932 100644
> > --- a/refs/packed-backend.c
> > +++ b/refs/packed-backend.c
> > @@ -1522,15 +1522,10 @@ static int packed_initial_transaction_commit(struct ref_store *ref_store,
> >  static int packed_delete_refs(struct ref_store *ref_store, const char *msg,
> >  			     struct string_list *refnames, unsigned int flags)
> >  {
> > -	struct packed_ref_store *refs =
> > -		packed_downcast(ref_store, REF_STORE_WRITE, "delete_refs");
> >  	struct strbuf err = STRBUF_INIT;
> >  	struct ref_transaction *transaction;
> > -	struct string_list_item *item;
> >  	int ret;
> >  
> > -	(void)refs; /* We need the check above, but don't use the variable */
> > -
> >  	if (!refnames->nr)
> >  		return 0;
> >  
> > @@ -1544,6 +1539,27 @@ static int packed_delete_refs(struct ref_store *ref_store, const char *msg,
> >  	if (!transaction)
> >  		return -1;
> >  
> > +	ret = packed_refs_delete_refs(ref_store, transaction,
> > +				      msg, refnames, flags);
> > +
> > +	ref_transaction_free(transaction);
> > +	return ret;
> > +}
> > +
> > +int packed_refs_delete_refs(struct ref_store *ref_store,
> > +			    struct ref_transaction *transaction,
> > +			    const char *msg,
> > +			    struct string_list *refnames,
> > +			    unsigned int flags)
> > +{
> > +	struct packed_ref_store *refs =
> > +		packed_downcast(ref_store, REF_STORE_WRITE, "delete_refs");
> > +	struct strbuf err = STRBUF_INIT;
> > +	struct string_list_item *item;
> > +	int ret;
> > +
> > +	(void)(refs); /* We need the check above, but don't use the variable */
> > +
> >  	for_each_string_list_item(item, refnames) {
> >  		if (ref_transaction_delete(transaction, item->string, NULL,
> >  					   flags, msg, &err)) {
> 
> I see you're just moving this code around, but FWIW we can just do this
> (also in the pre-image):
> 
> 	int packed_refs_delete_refs(...)
> 	{
> 		[declare variables]
>                 
>                 /* Assert ref store sanity */
>                 packed_downcast(ref_store, REF_STORE_WRITE, "delete_refs")
> 
>                 [...]
> 	}
> 
> Not sure it's good to change it around just for this mostly-move, just a
> note...

I think this change is trivial enough to make while at it.

Patrick

> > @@ -1554,7 +1570,6 @@ static int packed_delete_refs(struct ref_store *ref_store, const char *msg,
> >  	}
> >  
> >  	ret = ref_transaction_commit(transaction, &err);
> > -
> 
> Stray whitespace change.