Re: [PATCH next v2] log_ref_setup: don't return stack-allocated array

[Erick Mattos <erick.mattos@gmail.com>]

Hi there,

2010/6/10 Thomas Rast <trast@student.ethz.ch>
>
> 859c301 (refs: split log_ref_write logic into log_ref_setup,
> 2010-05-21) refactors the stack allocation of the log_file array into
> the new log_ref_setup() function, but passes it back to the caller.
>
> Since the original intent seems to have been to split the work between
> log_ref_setup and log_ref_write, make it the caller's responsibility
> to allocate the buffer.
>
> Signed-off-by: Thomas Rast <trast@student.ethz.ch>
> Reported-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> ---
>
> Sorry for the first one, that was completely botched and didn't even
> compile.
>
> This one does, and as an added bonus also passes some tests.
>
>  builtin/checkout.c |    4 ++--
>  refs.c             |   26 ++++++++++++--------------
>  refs.h             |    2 +-
>  3 files changed, 15 insertions(+), 17 deletions(-)
>
> diff --git a/builtin/checkout.c b/builtin/checkout.c
> index 5107eda..1994be9 100644
> --- a/builtin/checkout.c
> +++ b/builtin/checkout.c
> @@ -496,12 +496,12 @@ static void update_refs_for_switch(struct checkout_opts *opts,
>                if (opts->new_orphan_branch) {
>                        if (opts->new_branch_log && !log_all_ref_updates) {
>                                int temp;
> -                               char *log_file;
> +                               char log_file[PATH_MAX];
>                                char *ref_name = mkpath("refs/heads/%s", opts->new_orphan_branch);
>
>                                temp = log_all_ref_updates;
>                                log_all_ref_updates = 1;
> -                               if (log_ref_setup(ref_name, &log_file)) {
> +                               if (log_ref_setup(ref_name, log_file, sizeof(log_file))) {
>                                        fprintf(stderr, "Can not do reflog for '%s'\n",
>                                            opts->new_orphan_branch);
>                                        log_all_ref_updates = temp;
> diff --git a/refs.c b/refs.c
> index 3436649..6f486ae 100644
> --- a/refs.c
> +++ b/refs.c
> @@ -1262,43 +1262,41 @@ static int copy_msg(char *buf, const char *msg)
>        return cp - buf;
>  }
>
> -int log_ref_setup(const char *ref_name, char **log_file)
> +int log_ref_setup(const char *ref_name, char *logfile, int bufsize)
>  {
>        int logfd, oflags = O_APPEND | O_WRONLY;
> -       char logfile[PATH_MAX];
>
> -       git_snpath(logfile, sizeof(logfile), "logs/%s", ref_name);
> -       *log_file = logfile;
> +       git_snpath(logfile, bufsize, "logs/%s", ref_name);
>        if (log_all_ref_updates &&
>            (!prefixcmp(ref_name, "refs/heads/") ||
>             !prefixcmp(ref_name, "refs/remotes/") ||
>             !prefixcmp(ref_name, "refs/notes/") ||
>             !strcmp(ref_name, "HEAD"))) {
> -               if (safe_create_leading_directories(*log_file) < 0)
> +               if (safe_create_leading_directories(logfile) < 0)
>                        return error("unable to create directory for %s",
> -                                    *log_file);
> +                                    logfile);
>                oflags |= O_CREAT;
>        }
>
> -       logfd = open(*log_file, oflags, 0666);
> +       logfd = open(logfile, oflags, 0666);
>        if (logfd < 0) {
>                if (!(oflags & O_CREAT) && errno == ENOENT)
>                        return 0;
>
>                if ((oflags & O_CREAT) && errno == EISDIR) {
> -                       if (remove_empty_directories(*log_file)) {
> +                       if (remove_empty_directories(logfile)) {
>                                return error("There are still logs under '%s'",
> -                                            *log_file);
> +                                            logfile);
>                        }
> -                       logfd = open(*log_file, oflags, 0666);
> +                       logfd = open(logfile, oflags, 0666);
>                }
>
>                if (logfd < 0)
>                        return error("Unable to append to %s: %s",
> -                                    *log_file, strerror(errno));
> +                                    logfile, strerror(errno));
>        }
>
> -       adjust_shared_perm(*log_file);
> +       adjust_shared_perm(logfile);
>        close(logfd);
>        return 0;
>  }
> @@ -1309,14 +1307,14 @@ static int log_ref_write(const char *ref_name, const unsigned char *old_sha1,
>        int logfd, result, written, oflags = O_APPEND | O_WRONLY;
>        unsigned maxlen, len;
>        int msglen;
> -       char *log_file;
> +       char log_file[PATH_MAX];
>        char *logrec;
>        const char *committer;
>
>        if (log_all_ref_updates < 0)
>                log_all_ref_updates = !is_bare_repository();
>
> -       result = log_ref_setup(ref_name, &log_file);
> +       result = log_ref_setup(ref_name, log_file, sizeof(log_file));
>        if (result)
>                return result;
>
> diff --git a/refs.h b/refs.h
> index 594c9d9..762ce50 100644
> --- a/refs.h
> +++ b/refs.h
> @@ -69,7 +69,7 @@ extern void unlock_ref(struct ref_lock *lock);
>  extern int write_ref_sha1(struct ref_lock *lock, const unsigned char *sha1, const char *msg);
>
>  /** Setup reflog before using. **/
> -int log_ref_setup(const char *ref_name, char **log_file);
> +int log_ref_setup(const char *ref_name, char *logfile, int bufsize);
>
>  /** Reads log for the value of ref during at_time. **/
>  extern int read_ref_at(const char *ref, unsigned long at_time, int cnt, unsigned char *sha1, char **msg, unsigned long *cutoff_time, int *cutoff_tz, int *cutoff_cnt);
> --
> 1.7.1.553.ga798e


I can't get your point.

I don't see any improvement here.  Unless you want to get rid of using
references on calling functions which is only going to add another
buffer to the stack, sized PATH_MAX, once that log_file is going to be
really allocated in the heap after git_snpath().  As folks use to say
here: "changing six by half a dozen".

Even though I think you will need to turn static log_file or to call
git_snpath again in the calling functions for this proposed change,
don't you?

> Causes t5516 to fail, but only if I run it under valgrind.  (Ævar
> managed to trigger it in other ways apparently.)

I haven't ever seen this happening so I think you have found some
particularity of valgrind which could route a patch to it.

Kind regards