From: Michael Haggerty <mhagger@alum.mit.edu>
To: Jeff King <peff@peff.net>
Cc: Junio C Hamano <gitster@pobox.com>,
git@vger.kernel.org, David Turner <novalis@novalis.org>
Subject: Re: [PATCH v3 20/23] try_remove_empty_parents(): don't trash argument contents
Date: Mon, 2 Jan 2017 17:27:59 +0100 [thread overview]
Message-ID: <9215973c-8db1-8f5a-2dc7-3a0137dd5c62@alum.mit.edu> (raw)
In-Reply-To: <20161231064053.prvlw6x6qprzkmw7@sigill.intra.peff.net>
On 12/31/2016 07:40 AM, Jeff King wrote:
> On Sat, Dec 31, 2016 at 04:13:00AM +0100, Michael Haggerty wrote:
>
>> It's bad manners and surprising and therefore error-prone.
>
> Agreed.
>
> I wondered while reading your earlier patch whether the
> safe_create_leading_directories() function had the same problem, but it
> carefully replaces the NUL it inserts.
>
>> -static void try_remove_empty_parents(char *refname)
>> +static void try_remove_empty_parents(const char *refname)
>> {
>> + struct strbuf buf = STRBUF_INIT;
>> char *p, *q;
>> int i;
>> - p = refname;
>> +
>> + strbuf_addstr(&buf, refname);
>
> I see here you just make a copy. I think it would be enough to do:
>
>> @@ -2305,10 +2306,11 @@ static void try_remove_empty_parents(char *refname)
>> q--;
>> if (q == p)
>> break;
>> - *q = '\0';
>> - if (rmdir(git_path("%s", refname)))
>> + strbuf_setlen(&buf, q - buf.buf);
>> + if (rmdir(git_path("%s", buf.buf)))
>> break;
>
> *q = '\0';
> r = rmdir(git_path("%s", refname));
> *q = '/';
>
> if (r)
> break;
>
> or something. But I doubt the single allocation is breaking the bank,
> and it has the nice side effect that callers can pass in a const string
> (I didn't check yet whether that enables further cleanups).
The last patch in the series passes ref_update::refname to this
function, which is `const char *`. With your suggested change, either
that member would have to be made non-const, or it would have to be cast
to const at the `try_remove_empty_parents()` callsite.
Making the member non-const would be easy, though it loses a tiny bit of
documentation and safety against misuse. Also, scribbling even
temporarily over that member would mean that this code is not
thread-safe (though it seems unlikely that we would ever bother making
it multithreaded).
I think I prefer the current version because it loosens the coupling
between this function and its callers. But I don't mind either way if
somebody feels strongly about it.
As an aside, I wonder whether we would be discussing this at all if we
had stack-allocated strbufs that could be used without allocating heap
memory in the usual case.
Michael
next prev parent reply other threads:[~2017-01-02 16:28 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-31 3:12 [PATCH v3 00/23] Delete directories left empty after ref deletion Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 01/23] files_rename_ref(): tidy up whitespace Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 02/23] t5505: use "for-each-ref" to test for the non-existence of references Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 03/23] safe_create_leading_directories_const(): preserve errno Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 04/23] safe_create_leading_directories(): set errno on SCLD_EXISTS Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 05/23] raceproof_create_file(): new function Michael Haggerty
2016-12-31 6:11 ` Jeff King
2016-12-31 7:42 ` Michael Haggerty
2017-01-01 2:07 ` Junio C Hamano
2016-12-31 3:12 ` [PATCH v3 06/23] lock_ref_sha1_basic(): inline constant Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 07/23] lock_ref_sha1_basic(): use raceproof_create_file() Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 08/23] rename_tmp_log(): " Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 09/23] rename_tmp_log(): improve error reporting Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 10/23] log_ref_write(): inline function Michael Haggerty
2017-01-01 2:09 ` Junio C Hamano
2017-01-01 8:41 ` Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 11/23] log_ref_setup(): separate code for create vs non-create Michael Haggerty
2016-12-31 6:26 ` Jeff King
2016-12-31 7:52 ` Michael Haggerty
2017-01-01 3:28 ` Junio C Hamano
2017-01-01 8:45 ` Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 12/23] log_ref_setup(): improve robustness against races Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 13/23] log_ref_setup(): pass the open file descriptor back to the caller Michael Haggerty
2016-12-31 6:32 ` Jeff King
2016-12-31 7:58 ` Michael Haggerty
2016-12-31 17:58 ` Jeff King
2017-01-01 10:36 ` Junio C Hamano
2016-12-31 3:12 ` [PATCH v3 14/23] log_ref_write_1(): don't depend on logfile argument Michael Haggerty
2016-12-31 6:35 ` Jeff King
2016-12-31 8:01 ` Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 15/23] log_ref_setup(): manage the name of the reflog file internally Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 16/23] log_ref_write_1(): inline function Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 17/23] delete_ref_loose(): derive loose reference path from lock Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 18/23] delete_ref_loose(): inline function Michael Haggerty
2016-12-31 3:12 ` [PATCH v3 19/23] try_remove_empty_parents(): rename parameter "name" -> "refname" Michael Haggerty
2016-12-31 3:13 ` [PATCH v3 20/23] try_remove_empty_parents(): don't trash argument contents Michael Haggerty
2016-12-31 6:40 ` Jeff King
2017-01-02 16:27 ` Michael Haggerty [this message]
2017-01-02 17:10 ` Jeff King
2016-12-31 3:13 ` [PATCH v3 21/23] try_remove_empty_parents(): don't accommodate consecutive slashes Michael Haggerty
2017-01-01 2:30 ` Junio C Hamano
2017-01-01 5:59 ` Jeff King
2017-01-02 18:06 ` Michael Haggerty
2017-01-02 18:26 ` Jeff King
2016-12-31 3:13 ` [PATCH v3 22/23] try_remove_empty_parents(): teach to remove parents of reflogs, too Michael Haggerty
2016-12-31 3:13 ` [PATCH v3 23/23] files_transaction_commit(): clean up empty directories Michael Haggerty
2016-12-31 6:47 ` [PATCH v3 00/23] Delete directories left empty after ref deletion Jeff King
2017-01-01 2:32 ` Junio C Hamano
2017-01-01 9:24 ` Jacob Keller
2017-01-01 9:26 ` Jacob Keller
2017-01-01 12:43 ` Philip Oakley
2017-01-01 20:36 ` Jacob Keller
2017-01-02 4:19 ` Jeff King
2017-01-02 18:14 ` Michael Haggerty
2017-01-02 18:54 ` Jacob Keller
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