Re: [PATCH 2/4] reftable/stack: refactor reloading to use file descriptor
From: Junio C Hamano <hidden>
Date: 2024-01-10 19:57:29
Patrick Steinhardt [off-list ref] writes:
We're about to introduce a stat(3P)-based caching mechanism to reload the list of stacks only when it has changed. In order to avoid race conditions this requires us to have a file descriptor available that we can use to call fstat(3P) on. Prepare for this by converting the code to use `fd_read_lines()` so that we have the file descriptor readily available. ---
Missing sign-off. Other than that, the change is a refactoring that is very faithful to the original. Instead of doing the "open - pretend we opened an empty file if it does not exist - read - close" dance all inside the read_lines() call, this sort-of open codes the helper in this caller, so that later steps of this series can look at the file descriptor open to it. Looking good.
quoted hunk
reftable/stack.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-)diff --git a/reftable/stack.c b/reftable/stack.c index bf869a6772..b1ee247601 100644 --- a/reftable/stack.c +++ b/reftable/stack.c@@ -308,6 +308,7 @@ static int reftable_stack_reload_maybe_reuse(struct reftable_stack *st, struct timeval deadline; int64_t delay = 0; int tries = 0, err; + int fd = -1; err = gettimeofday(&deadline, NULL); if (err < 0)@@ -329,9 +330,19 @@ static int reftable_stack_reload_maybe_reuse(struct reftable_stack *st, if (tries > 3 && tv_cmp(&now, &deadline) >= 0) goto out; - err = read_lines(st->list_file, &names); - if (err < 0) - goto out; + fd = open(st->list_file, O_RDONLY); + if (fd < 0) { + if (errno != ENOENT) { + err = REFTABLE_IO_ERROR; + goto out; + } + + names = reftable_calloc(sizeof(char *)); + } else { + err = fd_read_lines(fd, &names); + if (err < 0) + goto out; + } err = reftable_stack_reload_once(st, names, reuse_open); if (!err)@@ -356,12 +367,16 @@ static int reftable_stack_reload_maybe_reuse(struct reftable_stack *st, names = NULL; free_names(names_after); names_after = NULL; + close(fd); + fd = -1; delay = delay + (delay * rand()) / RAND_MAX + 1; sleep_millisec(delay); } out: + if (fd >= 0) + close(fd); free_names(names); free_names(names_after); return err;