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authorPatrick Steinhardt <ps@pks.im>2020-04-02 07:10:02 (GMT)
committerJunio C Hamano <gitster@pobox.com>2020-04-02 18:09:49 (GMT)
commite48cf33b61b8fecf1558fb32fcf5ee2987e82890 (patch)
tree39e57596523fdf5bc71b71e6f047a4e0f9f9f642 /builtin/update-ref.c
parent94fd491a54b955990146f63e7283e9813dc85fef (diff)
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update-ref: implement interactive transaction handling
The git-update-ref(1) command can only handle queueing transactions right now via its "--stdin" parameter, but there is no way for users to handle the transaction itself in a more explicit way. E.g. in a replicated scenario, one may imagine a coordinator that spawns git-update-ref(1) for multiple repositories and only if all agree that an update is possible will the coordinator send a commit. Such a transactional session could look like > start < start: ok > update refs/heads/master $OLD $NEW > prepare < prepare: ok # All nodes have returned "ok" > commit < commit: ok or > start < start: ok > create refs/heads/master $OLD $NEW > prepare < fatal: cannot lock ref 'refs/heads/master': reference already exists # On all other nodes: > abort < abort: ok In order to allow for such transactional sessions, this commit introduces four new commands for git-update-ref(1), which matches those we have internally already with the exception of "start": - start: start a new transaction - prepare: prepare the transaction, that is try to lock all references and verify their current value matches the expected one - commit: explicitly commit a session, that is update references to match their new expected state - abort: abort a session and roll back all changes By design, git-update-ref(1) will commit as soon as standard input is being closed. While fine in a non-transactional world, it is definitely unexpected in a transactional world. Because of this, as soon as any of the new transactional commands is used, the default will change to aborting without an explicit "commit". To avoid a race between queueing updates and the first "prepare" that starts a transaction, the "start" command has been added to start an explicit transaction. Add some tests to exercise this new functionality. Signed-off-by: Patrick Steinhardt <ps@pks.im> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'builtin/update-ref.c')
-rw-r--r--builtin/update-ref.c106
1 files changed, 98 insertions, 8 deletions
diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 348407b..b74dd9a6 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -312,21 +312,80 @@ static void parse_cmd_option(struct ref_transaction *transaction,
die("option unknown: %s", next);
}
+static void parse_cmd_start(struct ref_transaction *transaction,
+ const char *next, const char *end)
+{
+ if (*next != line_termination)
+ die("start: extra input: %s", next);
+ puts("start: ok");
+}
+
+static void parse_cmd_prepare(struct ref_transaction *transaction,
+ const char *next, const char *end)
+{
+ struct strbuf error = STRBUF_INIT;
+ if (*next != line_termination)
+ die("prepare: extra input: %s", next);
+ if (ref_transaction_prepare(transaction, &error))
+ die("prepare: %s", error.buf);
+ puts("prepare: ok");
+}
+
+static void parse_cmd_abort(struct ref_transaction *transaction,
+ const char *next, const char *end)
+{
+ struct strbuf error = STRBUF_INIT;
+ if (*next != line_termination)
+ die("abort: extra input: %s", next);
+ if (ref_transaction_abort(transaction, &error))
+ die("abort: %s", error.buf);
+ puts("abort: ok");
+}
+
+static void parse_cmd_commit(struct ref_transaction *transaction,
+ const char *next, const char *end)
+{
+ struct strbuf error = STRBUF_INIT;
+ if (*next != line_termination)
+ die("commit: extra input: %s", next);
+ if (ref_transaction_commit(transaction, &error))
+ die("commit: %s", error.buf);
+ puts("commit: ok");
+ ref_transaction_free(transaction);
+}
+
+enum update_refs_state {
+ /* Non-transactional state open for updates. */
+ UPDATE_REFS_OPEN,
+ /* A transaction has been started. */
+ UPDATE_REFS_STARTED,
+ /* References are locked and ready for commit */
+ UPDATE_REFS_PREPARED,
+ /* Transaction has been committed or closed. */
+ UPDATE_REFS_CLOSED,
+};
+
static const struct parse_cmd {
const char *prefix;
void (*fn)(struct ref_transaction *, const char *, const char *);
unsigned args;
+ enum update_refs_state state;
} command[] = {
- { "update", parse_cmd_update, 3 },
- { "create", parse_cmd_create, 2 },
- { "delete", parse_cmd_delete, 2 },
- { "verify", parse_cmd_verify, 2 },
- { "option", parse_cmd_option, 1 },
+ { "update", parse_cmd_update, 3, UPDATE_REFS_OPEN },
+ { "create", parse_cmd_create, 2, UPDATE_REFS_OPEN },
+ { "delete", parse_cmd_delete, 2, UPDATE_REFS_OPEN },
+ { "verify", parse_cmd_verify, 2, UPDATE_REFS_OPEN },
+ { "option", parse_cmd_option, 1, UPDATE_REFS_OPEN },
+ { "start", parse_cmd_start, 0, UPDATE_REFS_STARTED },
+ { "prepare", parse_cmd_prepare, 0, UPDATE_REFS_PREPARED },
+ { "abort", parse_cmd_abort, 0, UPDATE_REFS_CLOSED },
+ { "commit", parse_cmd_commit, 0, UPDATE_REFS_CLOSED },
};
static void update_refs_stdin(void)
{
struct strbuf input = STRBUF_INIT, err = STRBUF_INIT;
+ enum update_refs_state state = UPDATE_REFS_OPEN;
struct ref_transaction *transaction;
int i, j;
@@ -374,14 +433,45 @@ static void update_refs_stdin(void)
if (strbuf_appendwholeline(&input, stdin, line_termination))
break;
+ switch (state) {
+ case UPDATE_REFS_OPEN:
+ case UPDATE_REFS_STARTED:
+ /* Do not downgrade a transaction to a non-transaction. */
+ if (cmd->state >= state)
+ state = cmd->state;
+ break;
+ case UPDATE_REFS_PREPARED:
+ if (cmd->state != UPDATE_REFS_CLOSED)
+ die("prepared transactions can only be closed");
+ state = cmd->state;
+ break;
+ case UPDATE_REFS_CLOSED:
+ die("transaction is closed");
+ break;
+ }
+
cmd->fn(transaction, input.buf + strlen(cmd->prefix) + !!cmd->args,
input.buf + input.len);
}
- if (ref_transaction_commit(transaction, &err))
- die("%s", err.buf);
+ switch (state) {
+ case UPDATE_REFS_OPEN:
+ /* Commit by default if no transaction was requested. */
+ if (ref_transaction_commit(transaction, &err))
+ die("%s", err.buf);
+ ref_transaction_free(transaction);
+ break;
+ case UPDATE_REFS_STARTED:
+ case UPDATE_REFS_PREPARED:
+ /* If using a transaction, we want to abort it. */
+ if (ref_transaction_abort(transaction, &err))
+ die("%s", err.buf);
+ break;
+ case UPDATE_REFS_CLOSED:
+ /* Otherwise no need to do anything, the transaction was closed already. */
+ break;
+ }
- ref_transaction_free(transaction);
strbuf_release(&err);
strbuf_release(&input);
}