On 02/05/2016 08:44 PM, David Turner wrote:
> Always handle non-normal (per-worktree or pseudo) refs in the files
> backend instead of alternate backends.
>
> Sometimes a ref transaction will update both a per-worktree ref and a
> normal ref. For instance, an ordinary commit might update
> refs/heads/master and HEAD (or at least HEAD's reflog).
>
> Updates to normal refs continue to go through the chosen backend.
>
> Updates to non-normal refs are moved to a separate files backend
> transaction.
>
> Signed-off-by: David Turner <dturner@xxxxxxxxxxxxxxxx>
> ---
> refs.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 79 insertions(+), 2 deletions(-)
>
> diff --git a/refs.c b/refs.c
> index 227c018..18ba356 100644
> --- a/refs.c
> +++ b/refs.c
> @@ -9,6 +9,11 @@
> #include "object.h"
> #include "tag.h"
>
> +static const char split_transaction_fail_warning[] = N_(
> + "A ref transaction was split across two refs backends. Part of the "
> + "transaction succeeded, but then the update to the per-worktree refs "
> + "failed. Your repository may be in an inconsistent state.");
> +
> /*
> * We always have a files backend and it is the default.
> */
> @@ -791,6 +796,13 @@ void ref_transaction_free(struct ref_transaction *transaction)
> free(transaction);
> }
>
> +static void add_update_obj(struct ref_transaction *transaction,
> + struct ref_update *update)
> +{
> + ALLOC_GROW(transaction->updates, transaction->nr + 1, transaction->alloc);
> + transaction->updates[transaction->nr++] = update;
> +}
> +
> static struct ref_update *add_update(struct ref_transaction *transaction,
> const char *refname)
> {
> @@ -798,8 +810,7 @@ static struct ref_update *add_update(struct ref_transaction *transaction,
> struct ref_update *update = xcalloc(1, sizeof(*update) + len);
>
> memcpy((char *)update->refname, refname, len); /* includes NUL */
> - ALLOC_GROW(transaction->updates, transaction->nr + 1, transaction->alloc);
> - transaction->updates[transaction->nr++] = update;
> + add_update_obj(transaction, update);
> return update;
> }
>
> @@ -1217,11 +1228,38 @@ static int dereference_symrefs(struct ref_transaction *transaction,
> return 0;
> }
>
> +/*
> + * Move all non-normal ref updates into a specially-created
> + * files-backend transaction
> + */
> +static int move_abnormal_ref_updates(struct ref_transaction *transaction,
> + struct ref_transaction *files_transaction,
> + struct strbuf *err)
> +{
> + int i;
> +
> + for (i = 0; i < transaction->nr; i++) {
> + int last;
> + struct ref_update *update = transaction->updates[i];
> +
> + if (ref_type(update->refname) == REF_TYPE_NORMAL)
> + continue;
> +
> + last = --transaction->nr;
> + transaction->updates[i] = transaction->updates[last];
> + add_update_obj(files_transaction, update);
> + }
> +
> + return 0;
> +}
> +
I think this function is incorrect. The update that was previously at
transaction->updates[i] never gets checked for abnormality. You could
fix that and also avoid gratuitously changing the order of the updates
like this:
static int move_abnormal_ref_updates(struct ref_transaction *transaction,
struct ref_transaction *files_transaction,
struct strbuf *err)
{
int i, normal_nr = 0;
for (i = 0; i < transaction->nr; i++) {
struct ref_update *update = transaction->updates[i];
if (ref_type(update->refname) == REF_TYPE_NORMAL)
transaction->updates[normal_nr++] = update;
else
add_update_obj(files_transaction, update);
}
transaction->nr = normal_nr;
return 0;
}
Another alternative would be to set
update->flags |= REF_ABNORMAL
for the abnormal references and *leave them* in the original transaction
while also adding them to files_transactions. Then teach non-files
backends to skip over updates with REF_ABNORMAL.
The reason I thought of this is that long-term I'd like to make it
possible for some reference updates to fail without aborting the
transaction. To implement that, we would want a way for
ref_transaction_commit() to report back to its caller *which* updates
failed, and an obvious way to do that would be to store the
reference-specific errors in struct ref_update. If you leave the
abnormal ref_updates in the main transaction, then my hoped-for change
would be easier.
But that's a separate and hypothetical idea, so you don't have to let it
influence how you implement this patch.
> int ref_transaction_commit(struct ref_transaction *transaction,
> struct strbuf *err)
> {
> int ret = -1;
> struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
> + struct string_list files_affected_refnames = STRING_LIST_INIT_NODUP;
> + struct ref_transaction *files_transaction = NULL;
>
> assert(err);
>
> @@ -1237,6 +1275,26 @@ int ref_transaction_commit(struct ref_transaction *transaction,
> if (ret)
> goto done;
>
> + if (the_refs_backend != &refs_be_files) {
> + files_transaction = ref_transaction_begin(err);
> + if (!files_transaction)
> + goto done;
> +
> + ret = move_abnormal_ref_updates(transaction, files_transaction,
> + err);
> + if (ret)
> + goto done;
> +
> + /* files backend commit */
> + if (get_affected_refnames(files_transaction,
> + &files_affected_refnames,
> + err)) {
> + ret = TRANSACTION_GENERIC_ERROR;
> + goto done;
> + }
> + }
> +
> + /* main backend commit */
> if (get_affected_refnames(transaction, &affected_refnames, err)) {
> ret = TRANSACTION_GENERIC_ERROR;
> goto done;
> @@ -1244,8 +1302,24 @@ int ref_transaction_commit(struct ref_transaction *transaction,
>
> ret = the_refs_backend->transaction_commit(transaction,
> &affected_refnames, err);
> + if (ret)
> + goto done;
> +
> + if (files_transaction) {
> + ret = refs_be_files.transaction_commit(files_transaction,
> + &files_affected_refnames,
> + err);
> + if (ret) {
> + warning(split_transaction_fail_warning);
> + goto done;
> + }
> + }
> +
> done:
> string_list_clear(&affected_refnames, 0);
> + string_list_clear(&files_affected_refnames, 0);
> + if (files_transaction)
> + ref_transaction_free(files_transaction);
> return ret;
> }
>
> @@ -1285,6 +1359,9 @@ int peel_ref(const char *refname, unsigned char *sha1)
> int create_symref(const char *ref_target, const char *refs_heads_master,
> const char *logmsg)
> {
> + if (ref_type(ref_target) != REF_TYPE_NORMAL)
> + return refs_be_files.create_symref(ref_target, refs_heads_master,
> + logmsg);
> return the_refs_backend->create_symref(ref_target, refs_heads_master,
> logmsg);
> }
>
Does initial_ref_transaction_commit() need the same treatment?
I think files_rename_ref() will break if one of the references is normal
and one is abnormal. I think it would be OK to prohibit renaming
abnormal refs entirely (can anybody think of an important use case?),
but that function should at least do the checks.
Michael
--
Michael Haggerty
mhagger@xxxxxxxxxxxx
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