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

> 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.