Subject: Re: [PATCH 10/15] refs.c: allow multiple reflog updates during a single transaction

From: Junio C Hamano <[email-masked]>
Date: Thu, 23 Oct 2014 11:54:43 -0700

Ronnie Sahlberg <[email-masked]> writes:

> @@ -3531,7 +3537,7 @@ struct ref_update {
>  	enum transaction_update_type update_type;
>  	unsigned char new_sha1[20];
>  	unsigned char old_sha1[20];
> -	int flags; /* REF_NODEREF? */
> +	int flags; /* REF_NODEREF? or private flags */

Not a very informative comment, I'd have to say.  How are users of
this API expected to avoid stepping on each others' and API
implementation's toes?

> @@ -3539,8 +3545,9 @@ struct ref_update {
>  
>  	/* used by reflog updates */
>  	int reflog_fd;
> -	struct lock_file reflog_lock;
> +	struct lock_file *reflog_lock;

What is this change about?

Does the lifetime rule for "struct lock_file" described in
Documentation/technical/api-lockfile.txt, namely, "once you call
hold_lock_file_* family on it, you cannot free it yourself", have
any implication on this?

> +	if (!(update->flags & UPDATE_REFLOG_NOLOCK))
> +		update->reflog_lock = xcalloc(1, sizeof(struct lock_file));
> +

Hmph, does this mean that the caller needs to keep track of the refs
it ever touched inside a single transaction, call this without nolock
on the first invocation on a particular ref and with nolock on the
subsequent invocation?

Or is the "caller" just implementation detail of the API and higher level
callers do not have to care?