[PATCH] mailmap: fix check for freeing memory

[PATCH] mailmap: fix check for freeing memory

[Stefan Beller]

The condition as it is written in that line was most likely intended to
check for the pointer passed to free(), rather than checking for the
'repo_abbrev', which is already checked against being non null at the
beginning of the function.

Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
---
 mailmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mailmap.c b/mailmap.c
index 44614fc..36d2a7a 100644
--- a/mailmap.c
+++ b/mailmap.c
@@ -139,35 +139,35 @@ static char *parse_name_and_email(char *buffer, char **name,
 static void read_mailmap_line(struct string_list *map, char *buffer,
 			      char **repo_abbrev)
 {
 	char *name1 = NULL, *email1 = NULL, *name2 = NULL, *email2 = NULL;
 	if (buffer[0] == '#') {
 		static const char abbrev[] = "# repo-abbrev:";
 		int abblen = sizeof(abbrev) - 1;
 		int len = strlen(buffer);
 
 		if (!repo_abbrev)
 			return;
 
 		if (len && buffer[len - 1] == '\n')
 			buffer[--len] = 0;
 		if (!strncmp(buffer, abbrev, abblen)) {
 			char *cp;
 
-			if (repo_abbrev)
+			if (*repo_abbrev)
 				free(*repo_abbrev);
 			*repo_abbrev = xmalloc(len);
 
 			for (cp = buffer + abblen; isspace(*cp); cp++)
 				; /* nothing */
 			strcpy(*repo_abbrev, cp);
 		}
 		return;
 	}
 	if ((name2 = parse_name_and_email(buffer, &name1, &email1, 0)) != NULL)
 		parse_name_and_email(name2, &name2, &email2, 1);
 
 	if (email1)
 		add_mapping(map, name1, email1, name2, email2);
 }
 
 static int read_mailmap_file(struct string_list *map, const char *filename,
-- 
1.8.4.rc3.1.gc1ebd90

Re: [PATCH] mailmap: fix check for freeing memory

[Thomas Rast]

Stefan Beller <stefanbeller@googlemail.com> writes:

> The condition as it is written in that line was most likely intended to
> check for the pointer passed to free(), rather than checking for the
> 'repo_abbrev', which is already checked against being non null at the
> beginning of the function.
[...]
> -			if (repo_abbrev)
> +			if (*repo_abbrev)
>  				free(*repo_abbrev);

But now the test is useless, because free(NULL) is defined to be a
no-op.

-- 
Thomas Rast
trast@{inf,student}.ethz.ch

Re: [PATCH] mailmap: fix check for freeing memory

[Jeff King]

On Tue, Aug 20, 2013 at 03:40:02PM +0200, Thomas Rast wrote:

> Stefan Beller <stefanbeller@googlemail.com> writes:
> 
> > The condition as it is written in that line was most likely intended to
> > check for the pointer passed to free(), rather than checking for the
> > 'repo_abbrev', which is already checked against being non null at the
> > beginning of the function.
> [...]
> > -			if (repo_abbrev)
> > +			if (*repo_abbrev)
> >  				free(*repo_abbrev);
> 
> But now the test is useless, because free(NULL) is defined to be a
> no-op.

Yeah, I think we should just drop the conditional completely.

I am not sure of the complete back-story. The earlier check for
repo_abbrev to be non-NULL was added by 8503ee4, after this check on
free() already existed. So that was when this conditional became
redundant.

But the line right after this one unconditionally assigns to
"*repo_abbrev", so we would always segfault in such a case anyway (which
is what 8503ee4 was fixing).

So I think it was either a misguided "don't pass NULL to free" check
that was simply wrong, or it was an incomplete "make sure repo_abbrev is
not NULL" check. And the first is useless, and the second is now
redundant due to 8503ee4. So it should simply be free().

-Peff

Re: [PATCH] mailmap: fix check for freeing memory

[Stefan Beller]

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On 08/20/2013 03:40 PM, Thomas Rast wrote:
> Stefan Beller <stefanbeller@googlemail.com> writes:
> 
>> The condition as it is written in that line was most likely intended to
>> check for the pointer passed to free(), rather than checking for the
>> 'repo_abbrev', which is already checked against being non null at the
>> beginning of the function.
> [...]
>> -			if (repo_abbrev)
>> +			if (*repo_abbrev)
>>  				free(*repo_abbrev);
> 
> But now the test is useless, because free(NULL) is defined to be a
> no-op.
> 

Yes, indeed. Thanks for reviewing.

Stepping two steps back, I am trying to figure out, what this repo_abrev
thing is doing, as I could find no documentation.

It's passed as a double pointer as declared in mailmap.h:
int read_mailmap(struct string_list *map, char **repo_abbrev);

However grepping for "read_mailmap(" (bracket to prevent finding 
read_mailmap_XXX as often used in mailmap.c itself) 
	grep -nHIirF --exclude-dir=.git -- "read_mailmap("
throughout all the sources I just find one occurence having the
second argument not being 'NULL' and that is in 
	builtin/shortlog.c:212:	read_mailmap(&log->mailmap, &log->common_repo_prefix);

which turns out to be:

void shortlog_init(struct shortlog *log)
{
	memset(log, 0, sizeof(*log));

	read_mailmap(&log->mailmap, &log->common_repo_prefix);
	...

So we're passing there an address, which was just set to zero.
This is the only occurence of passing a value at all and the value
being passed is 0, so the free in the original patch doesn't need 
that check either.

As I am resending the patch, could somebody please explain me
the mechanism of the "# repo-abbrev:" line? Even git itself doesn't
use it in the .mailmap file, but a quick google search shows up only
kernel repositories.

Stefan



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[PATCH] mailmap: remove redundant check for freeing memory

[Stefan Beller]

The condition as it is written in that line has already been checked
in the beginning of the function, which was introduced in
8503ee4 (2007-05-01, Fix read_mailmap to handle a caller uninterested
in repo abbreviation)

Helped-by: Jeff King <peff@peff.net>
Helped-by: Thomas Rast <trast@inf.ethz.ch>
Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
---
 mailmap.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mailmap.c b/mailmap.c
index 44614fc..7d5caa6 100644
--- a/mailmap.c
+++ b/mailmap.c
@@ -153,8 +153,7 @@ static void read_mailmap_line(struct string_list *map, char *buffer,
 		if (!strncmp(buffer, abbrev, abblen)) {
 			char *cp;
 
-			if (repo_abbrev)
-				free(*repo_abbrev);
+			free(*repo_abbrev);
 			*repo_abbrev = xmalloc(len);
 
 			for (cp = buffer + abblen; isspace(*cp); cp++)
-- 
1.8.4.rc3.1.gc1ebd90

Re: [PATCH] mailmap: remove redundant check for freeing memory

[Jeff King]

On Tue, Aug 20, 2013 at 04:18:00PM +0200, Stefan Beller wrote:

> The condition as it is written in that line has already been checked
> in the beginning of the function, which was introduced in
> 8503ee4 (2007-05-01, Fix read_mailmap to handle a caller uninterested
> in repo abbreviation)
> 
> Helped-by: Jeff King <peff@peff.net>
> Helped-by: Thomas Rast <trast@inf.ethz.ch>
> Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
> ---

This version looks good to me.  Thanks.

-Peff

Re: [PATCH] mailmap: fix check for freeing memory

[Thomas Rast]

Stefan Beller <stefanbeller@googlemail.com> writes:

> As I am resending the patch, could somebody please explain me
> the mechanism of the "# repo-abbrev:" line? Even git itself doesn't
> use it in the .mailmap file, but a quick google search shows up only
> kernel repositories.

I had no idea (we really lack documentation on this), but some history
digging shows this:

  commit 7595e2ee6ef9b35ebc8dc45543723e1d89765ce3
  Author: Junio C Hamano <junkio@cox.net>
  Date:   Sat Nov 25 00:07:54 2006 -0800

      git-shortlog: make common repository prefix configurable with .mailmap
      
      The code had "/pub/scm/linux/kernel/git/" hardcoded which was
      too specific to the kernel project.
      
      With this, a line in the .mailmap file:
      
          # repo-abbrev: /pub/scm/linux/kernel/git/
      
      can be used to cause the substring to be abbreviated to /.../
      on the title line of the commit message.
      
      Signed-off-by: Junio C Hamano <junkio@cox.net>

It apparently serves to abbreviate commits coming from pull requests,
with a subject like

  Merge branch 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux

-- 
Thomas Rast
trast@{inf,student}.ethz.ch

Re: [PATCH] mailmap: fix check for freeing memory

[Stefan Beller]

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On 08/20/2013 04:23 PM, Thomas Rast wrote:
> Stefan Beller <stefanbeller@googlemail.com> writes:
> 
>> As I am resending the patch, could somebody please explain me
>> the mechanism of the "# repo-abbrev:" line? Even git itself doesn't
>> use it in the .mailmap file, but a quick google search shows up only
>> kernel repositories.
> 
> I had no idea (we really lack documentation on this), but some history
> digging shows this:
> 
>   commit 7595e2ee6ef9b35ebc8dc45543723e1d89765ce3
>   Author: Junio C Hamano <junkio@cox.net>
>   Date:   Sat Nov 25 00:07:54 2006 -0800
> 
>       git-shortlog: make common repository prefix configurable with .mailmap
>       
>       The code had "/pub/scm/linux/kernel/git/" hardcoded which was
>       too specific to the kernel project.
>       
>       With this, a line in the .mailmap file:
>       
>           # repo-abbrev: /pub/scm/linux/kernel/git/
>       
>       can be used to cause the substring to be abbreviated to /.../
>       on the title line of the commit message.
>       
>       Signed-off-by: Junio C Hamano <junkio@cox.net>
> 
> It apparently serves to abbreviate commits coming from pull requests,
> with a subject like
> 
>   Merge branch 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux
> 

Thanks for looking through the history, I need to adapt my search patterns. ;)

Personally I have the feel this is a very kernel specific, but also 
useful thing to have. So I would definitely not drop it, but maybe move
it to another place, such as in the .git/config file. 
Then anybody can configure it themselves and maybe even have multiple
abbreviation lines possible.
It's very likely nowadays that there are repos at various different
hosting sites, so just one abbreviation would not cut it anymore.

Or as Jeff just mentioned in his email, it's there for historical
purpose, but not needed anymore as git-merge produces nicer commit
messages there.

As proposed I checked recent kernel history and saw:

$ git log --min-parents=2 --oneline 
d6a5e06 Merge git://git.kernel.org/pub/scm/linux/kernel/git/steve/gfs2-3.0-fixes
7067552 Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
e91dade Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
fbf2184 Merge branch 'drm-fixes' of git://people.freedesktop.org/~airlied/linux
3387ed8 Merge tag 'drm-intel-fixes-2013-08-15' of git://people.freedesktop.org/~danvet/drm-intel
d2b2c08 Merge branch 'drm-fixes-3.11' of git://people.freedesktop.org/~agd5f/linux
50e37cc Merge branch 'for-3.11-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup
a08797e Merge tag 'ext4_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4
2620bf0 Merge branch 'fixes' of git://git.linaro.org/people/rmk/linux-arm
359d16c Merge branch 'for-3.11' of git://git.kernel.org/pub/scm/linux/kernel/git/geert/linux-m68k
0f7dd1a Merge tag 'clk-fixes-for-linus' of git://git.linaro.org/people/mturquette/linux
2d2843e Merge tag 'pm-3.11-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
f43c606 Merge tag 'sound-3.11' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound
89cb9ae Merge tag 'usb-3.11-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb

in their .mailmap it read:
	# repo-abbrev: /pub/scm/linux/kernel/git/

So the abbreviation doesn't take place, can this feature be turned off?
I'm still confused by that feature.

Thanks,
Stefan




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Re: [PATCH] mailmap: fix check for freeing memory

[Jeff King]

On Tue, Aug 20, 2013 at 04:38:17PM +0200, Stefan Beller wrote:

> As proposed I checked recent kernel history and saw:
> 
> $ git log --min-parents=2 --oneline 
> d6a5e06 Merge git://git.kernel.org/pub/scm/linux/kernel/git/steve/gfs2-3.0-fixes
> 7067552 Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
> e91dade Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
> fbf2184 Merge branch 'drm-fixes' of git://people.freedesktop.org/~airlied/linux
> 3387ed8 Merge tag 'drm-intel-fixes-2013-08-15' of git://people.freedesktop.org/~danvet/drm-intel
> d2b2c08 Merge branch 'drm-fixes-3.11' of git://people.freedesktop.org/~agd5f/linux
> 50e37cc Merge branch 'for-3.11-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup
> a08797e Merge tag 'ext4_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4
> 2620bf0 Merge branch 'fixes' of git://git.linaro.org/people/rmk/linux-arm
> 359d16c Merge branch 'for-3.11' of git://git.kernel.org/pub/scm/linux/kernel/git/geert/linux-m68k
> 0f7dd1a Merge tag 'clk-fixes-for-linus' of git://git.linaro.org/people/mturquette/linux
> 2d2843e Merge tag 'pm-3.11-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
> f43c606 Merge tag 'sound-3.11' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound
> 89cb9ae Merge tag 'usb-3.11-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb
> 
> in their .mailmap it read:
> 	# repo-abbrev: /pub/scm/linux/kernel/git/
> 
> So the abbreviation doesn't take place, can this feature be turned off?
> I'm still confused by that feature.

It _only_ impacts git-shortlog, not git-log or other traversals. Making
it an even more dubious feature, IMHO.

-Peff

Re: [PATCH] mailmap: fix check for freeing memory

[Junio C Hamano]

Jeff King <peff@peff.net> writes:

> It _only_ impacts git-shortlog, not git-log or other traversals. Making
> it an even more dubious feature, IMHO.

I think this was done by an explicit end user request for shortlog.

As you mentioned, merge gives readable merge log messages, but it
deliberately uses the real URL, not your personal nickname for the
remote when writing the title line of a merge, i.e.

	Merge [branch <x> of ]<repoURL>

so it would be helped by the repository abbreviation.  It probably
was an oversight that we did not extend it to the rest of the log
family.

Re: [PATCH] mailmap: fix check for freeing memory

[Jeff King]

On Tue, Aug 20, 2013 at 10:18:08AM -0700, Junio C Hamano wrote:

> As you mentioned, merge gives readable merge log messages, but it
> deliberately uses the real URL, not your personal nickname for the
> remote when writing the title line of a merge, i.e.
> 
> 	Merge [branch <x> of ]<repoURL>
> 
> so it would be helped by the repository abbreviation.  It probably
> was an oversight that we did not extend it to the rest of the log
> family.

Ah, yeah, I suppose git-pull will still do that. I was thinking of a
direct git-merge of a tracking branch, which would end up with:

  Merge remote-tracking branch 'origin/master'

whereas "git pull origin master" in the same case would say:

  Merge branch 'master' of git://github.com/gitster/git

Still, I do not think anybody but the kernel is using it. Most people
simply have shorter URLs that do not need abbreviated (e.g., the GitHub
one shown above). And searching for instances on GitHub yields only the
kernel:

  https://github.com/search?q=repo-abbrev+path%3A.mailmap&type=Code

Anyway, I am not proposing ripping the feature out. It just seems like
it does not have a lot of users, and it is not worth worrying much about
trying to extend it.

-Peff

Re: [PATCH] mailmap: fix check for freeing memory

[Jeff King]

On Tue, Aug 20, 2013 at 04:17:07PM +0200, Stefan Beller wrote:

> Stepping two steps back, I am trying to figure out, what this repo_abrev
> thing is doing, as I could find no documentation.

It's meant to abbreviate long pathnames in subject lines. As you noted,
the kernel .mailmap has:

  # repo-abbrev: /pub/scm/linux/kernel/git/

Try "git shortlog" in the kernel and grep for "..." to see its effect.

It is IMHO a misfeature to have it as part of .mailmap, but it is there
for historical reasons. And I think it is not really needed these days
anyway, as the messages created by git-merge are nicer to read in the
first place (and people tend to use nice readable URLs for accessing
one-off git pulls, too).

> So we're passing there an address, which was just set to zero.
> This is the only occurence of passing a value at all and the value
> being passed is 0, so the free in the original patch doesn't need
> that check either.

Right. I think the intent was to free a previously found repo-abbrev
line to avoid leaking memory (although arguably, it would make sense to
keep a list and abbreviate all that we find, I don't think anybody cares
anymore for the reasons I stated above).

-Peff