reftable/stack: fix error handling in `reftable_stack_init_addition()`

In `reftable_stack_init_addition()` we call `stack_uptodate()` after
having created the lockfile to check whether the stack was modified
concurrently, which is indicated by a positive return code from the
latter function. If so, we return a `REFTABLE_LOCK_ERROR` to the caller
and abort the addition.

The error handling has an off-by-one though because we check whether the
error code is `> 1` instead of `> 0`. Thus, instead of returning the
locking error, we would return a positive value. One of the callers of
`reftable_stack_init_addition()` works around this bug by repeating the
error code check without the off-by-one. But other callers are subtly
broken by this bug.

Fix this by checking for `err > 0` instead. This has the consequence
that `reftable_stack_init_addition()` won't ever return a positive error
code anymore, but will instead return `REFTABLE_LOCK_ERROR` now. Thus,
we can drop the check for a positive error code in `stack_try_add()`
now.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/reftable/stack.c b/reftable/stack.c
index 1ecf1b9751ce4975580ab7deed2bbe2a9a7847bc..92d9a7facb0ffcec02f4dc050c2b874d36602c55 100644 (file)
--- a/reftable/stack.c
+++ b/reftable/stack.c
@@ -590,8 +590,7 @@ static int reftable_stack_init_addition(struct reftable_addition *add,
        err = stack_uptodate(st);
        if (err < 0)
                goto done;
-
-       if (err > 1) {
+       if (err > 0) {
                err = REFTABLE_LOCK_ERROR;
                goto done;
        }
@@ -713,10 +712,6 @@ static int stack_try_add(struct reftable_stack *st,
        int err = reftable_stack_init_addition(&add, st);
        if (err < 0)
                goto done;
-       if (err > 0) {
-               err = REFTABLE_LOCK_ERROR;
-               goto done;
-       }
 
        err = reftable_addition_add(&add, write_table, arg);
        if (err < 0)