[PATCH] log which temporary file could not be created

[PATCH] log which temporary file could not be created

[Arnout Engelen]

When creating a temporary file, log the template. Useful for making debugging 
problems like file permission mistakes easier.

Signed-off-by: Arnout Engelen <arnouten@bzzt.net>

---
 wrapper.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/wrapper.c b/wrapper.c
index fd8ead3..68053cd 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -215,7 +215,7 @@ int xmkstemp(char *template)
 
 	fd = mkstemp(template);
 	if (fd < 0)
-		die_errno("Unable to create temporary file");
+		die_errno("Unable to create temporary file '%s'", template);
 	return fd;
 }
 
@@ -225,7 +225,7 @@ int xmkstemp_mode(char *template, int mode)
 
 	fd = git_mkstemp_mode(template, mode);
 	if (fd < 0)
-		die_errno("Unable to create temporary file");
+		die_errno("Unable to create temporary file '%s'", template);
 	return fd;
 }
 
-- 
1.7.2.3

Re: [PATCH] log which temporary file could not be created

[Jonathan Nieder]

Hi,

Arnout Engelen wrote:

> When creating a temporary file, log the template.

Since mkstemp modifies its template, these hopefully would print the
actual filename on errors.  Examples:

	fatal: Unable to create temporary file '.merge_file_Sc7R5c': File exists
	fatal: Unable to create temporary file 'newrepo/.git/tOWHcxk': No space left on device

Unfortunately some mkstemp()s (such as that used to implement
git_mkstemp_mode()) clear the template on error, which would result in

	fatal: Unable to create temporary file '': Permission denied

What should git do in this situation?

> Useful for making debugging 
> problems like file permission mistakes easier.

Agreed.  Thanks.

Re: [PATCH] log which temporary file could not be created

[Arnout Engelen]

On Sat, Oct 09, 2010 at 09:41:24PM -0500, Jonathan Nieder wrote:
> Arnout Engelen wrote:
> > When creating a temporary file, log the template.
> 
> Since mkstemp modifies its template, these hopefully would print the
> actual filename on errors.  Examples:
> 
> 	fatal: Unable to create temporary file '.merge_file_Sc7R5c': File exists
> 	fatal: Unable to create temporary file 'newrepo/.git/tOWHcxk': No space left on device

Perhaps we should also log the current working directory when the temporary 
filename is relative?

> Unfortunately some mkstemp()s (such as that used to implement
> git_mkstemp_mode()) clear the template on error, which would result in
> 
> 	fatal: Unable to create temporary file '': Permission denied
> 
> What should git do in this situation?

Perhaps we should strdup() the template before mkstemp(), and log the 
strdup()'ed template when the original has been cleared?


Arnout

Re: [PATCH] log which temporary file could not be created

[Jonathan Nieder]

Arnout Engelen wrote:
> On Sat, Oct 09, 2010 at 09:41:24PM -0500, Jonathan Nieder wrote:

>> 	fatal: Unable to create temporary file '.merge_file_Sc7R5c': File exists
>> 	fatal: Unable to create temporary file 'newrepo/.git/tOWHcxk': No space left on device
>
> Perhaps we should also log the current working directory when the temporary 
> filename is relative?

Let's step back for a moment.  Was there an example that prompted
this patch?  Were you aware of where git would be trying to create
files in that example?  (I'm genuinely curious.)

Converting the filename to an absolute path with make_absolute_path
might be useful, but I am not entirely sure it is worth the
complication.

>> 	fatal: Unable to create temporary file '': Permission denied
>>
>> What should git do in this situation?
>
> Perhaps we should strdup() the template before mkstemp(), and log the 
> strdup()'ed template when the original has been cleared?

Is it be preferable for the filename to always have XXXXXX in it?  If
so, then copying it into a temporary buffer (on-stack, preferably)
could be a sane solution, yes.

Jonathan

Re: [PATCH] log which temporary file could not be created

[Arnout Engelen]

On Sun, Oct 10, 2010 at 01:09:09PM -0500, Jonathan Nieder wrote:
> Arnout Engelen wrote:
> > On Sat, Oct 09, 2010 at 09:41:24PM -0500, Jonathan Nieder wrote:
> >> 	fatal: Unable to create temporary file '.merge_file_Sc7R5c': File exists
> >> 	fatal: Unable to create temporary file 'newrepo/.git/tOWHcxk': No space left on device
> >
> > Perhaps we should also log the current working directory when the temporary 
> > filename is relative?
> 
> Let's step back for a moment.  Was there an example that prompted
> this patch?  

Yes: I was trying to do an initial push to a sf.net git repo, and this gave me:

arnouten@bird:~/asdf/notion$ git push sourceforge master
raboofje@notion.git.sourceforge.net's password: 
Counting objects: 21542, done.
Compressing objects: 100% (4179/4179), done.
fatal: Unable to create temporary file: Permission denied
error: pack-objects died of signal 13
error: pack-objects died with strange error
error: failed to push some refs to 'ssh://raboofje@notion.git.sourceforge.net/gitroot/notion/notion'
arnouten@bird:~/asdf/notion$

This seems to have been an error at the server side. I never did find out what
exactly went wrong - I just re-initialized the repo using the shell access and
all was fine after that.

> Were you aware of where git would be trying to create
> files in that example?  (I'm genuinely curious.)

No clue - but I'm not very into git 'internals' yet.

> Converting the filename to an absolute path with make_absolute_path
> might be useful, but I am not entirely sure it is worth the
> complication.
> 
> >> 	fatal: Unable to create temporary file '': Permission denied
> >>
> >> What should git do in this situation?
> >
> > Perhaps we should strdup() the template before mkstemp(), and log the 
> > strdup()'ed template when the original has been cleared?
> 
> Is it be preferable for the filename to always have XXXXXX in it?  If
> so, then copying it into a temporary buffer (on-stack, preferably)
> could be a sane solution, yes.

I'm not sure about 'always', but it'd be nice to have something to fall back 
to when the mkstemp clears the template.


Kind regards,

Arnout

Re: [PATCH] log which temporary file could not be created

[Junio C Hamano]

Jonathan Nieder <jrnieder@gmail.com> writes:

> Arnout Engelen wrote:
>> On Sat, Oct 09, 2010 at 09:41:24PM -0500, Jonathan Nieder wrote:
>
>>> 	fatal: Unable to create temporary file '.merge_file_Sc7R5c': File exists
>>> 	fatal: Unable to create temporary file 'newrepo/.git/tOWHcxk': No space left on device
>>
>> Perhaps we should also log the current working directory when the temporary 
>> filename is relative?
>
> Let's step back for a moment.  Was there an example that prompted
> this patch?  Were you aware of where git would be trying to create
> files in that example?  (I'm genuinely curious.)
>
> Converting the filename to an absolute path with make_absolute_path
> might be useful, but I am not entirely sure it is worth the
> complication.

For that matter, I am not sure if it is worth the strdup "just in case it
fails" either.

[PATCH] send-pack: avoid redundant "pack-objects died with strange error"

[Jonathan Nieder]

Arnout Engelen wrote:

> arnouten@bird:~/asdf/notion$ git push sourceforge master
> raboofje@notion.git.sourceforge.net's password: 
> Counting objects: 21542, done.
> Compressing objects: 100% (4179/4179), done.
> fatal: Unable to create temporary file: Permission denied
> error: pack-objects died of signal 13
> error: pack-objects died with strange error
> error: failed to push some refs to 'ssh://raboofje@notion.git.sourceforge.net/gitroot/notion/notion' arnouten@bird:~/asdf/notion$

That reminds me: the output seems more noisy than it needs to be, no?

-- 8< --
Subject: send-pack: avoid redundant "pack-objects died with strange error"

Saying "pack-objects died with strange error" after "pack-objects
died of signal 13" seems kind of redundant.  The latter was
introduced when send-pack switched to the run-command API, which
reports abnormal exits on behalf of the caller.

Normal exits with nonzero status are not reported by run-command,
though.  Be more helpful in reporting them by including the exit
status while at it.

The result should look something like this:

	$ git push sf master
	Counting objects: 21542, done.
	Compressing objects: 100% (4179/4179), done.
	fatal: Unable to create temporary file: Permission denied
	error: pack-objects died of signal 13
	error: failed to push some refs to 'ssh://sf.net/gitroot/project/project'
	$

Or in the "controlled exit" case:

	[...]
	error: pack-objects died with status 128
	error: failed to push some refs to 'ssh://example.com/foo/bar'
	$

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
 builtin/send-pack.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/builtin/send-pack.c b/builtin/send-pack.c
index 481602d..51b722b 100644
--- a/builtin/send-pack.c
+++ b/builtin/send-pack.c
@@ -50,7 +50,7 @@ static int pack_objects(int fd, struct ref *refs, struct extra_have_objects *ext
 		NULL,
 	};
 	struct child_process po;
-	int i;
+	int i, status;
 
 	i = 4;
 	if (args->use_thin_pack)
@@ -100,9 +100,10 @@ static int pack_objects(int fd, struct ref *refs, struct extra_have_objects *ext
 		po.out = -1;
 	}
 
-	if (finish_command(&po))
-		return error("pack-objects died with strange error");
-	return 0;
+	status = finish_command(&po);
+	if (status > 0)
+		error("pack-objects died with status %d", status);
+	return status;
 }
 
 static int receive_status(int in, struct ref *refs)
-- 
1.7.2.3

[PATCH v2] send-pack: avoid redundant "pack-objects died with strange error"

[Jonathan Nieder]

Saying "pack-objects died with strange error" after "pack-objects
died of signal 13" seems kind of redundant.  The latter was
introduced when send-pack switched to the run-command API, which
reports abnormal exits on behalf of the caller.

Normal exits with nonzero status are not reported by run-command,
though.  Be more helpful in reporting them by including the exit
status while at it (and be sure to continue to return a value
less than zero from pack_objects() for that case).

The result should look something like this:

	$ git push sf master
	Counting objects: 21542, done.
	Compressing objects: 100% (4179/4179), done.
	fatal: Unable to create temporary file: Permission denied
	error: pack-objects died of signal 13
	error: failed to push some refs to 'ssh://sf.net/gitroot/project/project'
	$

Or in the "controlled exit" case:

	[...]
	error: pack-objects died with status 128
	error: failed to push some refs to 'ssh://example.com/foo/bar'
	$

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
Jonathan Nieder wrote:

> +++ b/builtin/send-pack.c
> @@ -100,9 +100,10 @@ static int pack_objects(int fd, struct ref *refs, struct extra_have_objects *ext
>  		po.out = -1;
>  	}
>  
> -	if (finish_command(&po))
> -		return error("pack-objects died with strange error");
> +	status = finish_command(&po);
> +	if (status > 0)
> +		error("pack-objects died with status %d", status);
> +	return status;

Caller:

	if (pack_objects(...) < 0)

So making pack_objects return >0 where it used to return <0 would be
a regression. :(  An updated patch with the following minimal fix
squashed in follows.

	status = finish_command(&po);
	if (status > 0)
 -		error("pack-objects died with status %d", status);
 +		return error("pack-objects died with status %d", status);
	return status;
  }

 builtin/send-pack.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/builtin/send-pack.c b/builtin/send-pack.c
index 481602d..8854748 100644
--- a/builtin/send-pack.c
+++ b/builtin/send-pack.c
@@ -50,7 +50,7 @@ static int pack_objects(int fd, struct ref *refs, struct extra_have_objects *ext
 		NULL,
 	};
 	struct child_process po;
-	int i;
+	int i, status;
 
 	i = 4;
 	if (args->use_thin_pack)
@@ -100,9 +100,10 @@ static int pack_objects(int fd, struct ref *refs, struct extra_have_objects *ext
 		po.out = -1;
 	}
 
-	if (finish_command(&po))
-		return error("pack-objects died with strange error");
-	return 0;
+	status = finish_command(&po);
+	if (status > 0)
+		return error("pack-objects died with status %d", status);
+	return status;
 }
 
 static int receive_status(int in, struct ref *refs)
-- 
1.7.2.3

Re: [PATCH v2] send-pack: avoid redundant "pack-objects died with strange error"

[Johannes Sixt]

On Samstag, 16. Oktober 2010, Jonathan Nieder wrote:
> Saying "pack-objects died with strange error" after "pack-objects
> died of signal 13" seems kind of redundant.  The latter was
> introduced when send-pack switched to the run-command API, which
> reports abnormal exits on behalf of the caller.
>
> Normal exits with nonzero status are not reported by run-command,
> though.

The rationale for this is the assumption that before a program or script exits 
with non-zero status, it will have reported an error.

> Or in the "controlled exit" case:
>
> 	[...]
> 	error: pack-objects died with status 128
> 	error: failed to push some refs to 'ssh://example.com/foo/bar'

I sense that this quote is not complete. Did you strip some error message by 
writing just "[...]"?

> -	if (finish_command(&po))
> -		return error("pack-objects died with strange error");
> -	return 0;
> +	status = finish_command(&po);
> +	if (status > 0)
> +		return error("pack-objects died with status %d", status);
> +	return status;

Ideally, this should really just be

	if (finish_command(&po))
		return -1;

-- Hannes

[PATCH v3] send-pack: avoid redundant "pack-objects died with strange error"

[Jonathan Nieder]

Saying "pack-objects died with strange error" after "pack-objects died
of signal 13" seems kind of redundant.  The latter message was
introduced when the run-command API changed to report abnormal exits
on behalf of the caller (v1.6.5-rc0~86^2~5, 2009-07-04).

Similarly, after a controlled pack-objects failure (detectable as a
normal exit with nonzero status), a "died with strange error" message
would be redundant next to the message from pack-objects itself.

So leave off the "strange error" messages.

The result should look something like this:

	$ git push sf master
	Counting objects: 21542, done.
	Compressing objects: 100% (4179/4179), done.
	fatal: Unable to create temporary file: Permission denied
	error: pack-objects died of signal 13
	error: failed to push some refs to 'ssh://sf.net/gitroot/project/project'
	$

Or in the "controlled exit" case (contrived example):

	[...]
	fatal: delta size changed
	error: failed to push some refs to 'ssh://example.com/foo/bar'
	$

Improved-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
On Sat, Oct 16, 2010 at 11:25:33AM +0200, Johannes Sixt wrote:
> On Samstag, 16. Oktober 2010, Jonathan Nieder wrote:

>> 	[...]
>> 	error: pack-objects died with status 128
>> 	error: failed to push some refs to 'ssh://example.com/foo/bar'
>
> I sense that this quote is not complete. Did you strip some error message by 
> writing just "[...]"?

That was invented example output.

Googling for "pack-objects died with strange error" gives me [1], with
v1.6.2:

	$ git push
	Counting objects: 68, done.
	Delta compression using 2 threads.
	Compressing objects: 100% (50/50), done.
	Connection to SERVER closed by remote host.
	error: pack-objects died with strange error
	error: failed to push some refs to 'SERVER:PROJECT.git'

and [2], with v1.6.4.4:

	Counting objects: 4364, done.
	Delta compression using up to 2 threads.
	Compressing objects: 100% (4240/4240), done.
	error: pack-objects died with strange error | 44 KiB/s   
	error: failed to push some refs to 'mysite:main_site_repo'

and some similar examples.  All involve git versions before
v1.6.5-rc0~86^2~5 (run_command: report system call errors instead of
returning error codes, 2009-07-04) and after a triage turn out to be
signals.

Let's go with your fix (thanks!).

[1] http://stackoverflow.com/questions/718962/git-push-error-pack-objects-died-with-strange-error
[2] http://stackoverflow.com/questions/1781013/git-error-failed-to-push-some-refs-pack-objects-died-with-strange-error

 builtin/send-pack.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/builtin/send-pack.c b/builtin/send-pack.c
index 481602d..8aa3031 100644
--- a/builtin/send-pack.c
+++ b/builtin/send-pack.c
@@ -101,7 +101,7 @@ static int pack_objects(int fd, struct ref *refs, struct extra_have_objects *ext
 	}
 
 	if (finish_command(&po))
-		return error("pack-objects died with strange error");
+		return -1;
 	return 0;
 }
 
-- 
1.7.2.3

Re: [PATCH] log which temporary file could not be created

[Arnout Engelen]

On Mon, Oct 11, 2010 at 08:56:59PM -0700, Junio C Hamano wrote:
> Jonathan Nieder <jrnieder@gmail.com> writes:
> >> On Sat, Oct 09, 2010 at 09:41:24PM -0500, Jonathan Nieder wrote:
> >>> 	fatal: Unable to create temporary file '.merge_file_Sc7R5c': File exists
> >>> 	fatal: Unable to create temporary file 'newrepo/.git/tOWHcxk': No space left on device
> >
> > Converting the filename to an absolute path with make_absolute_path
> > might be useful, but I am not entirely sure it is worth the
> > complication.
> 
> I am not sure if it is worth the strdup "just in case it fails" either.

I think it's valuable to give better error messages. A strdup/strncpy does not
take much resources (especially compared to creating the temporary file), and 
makes the code only slightly less readable as the change is fairly local. 

Below is an updated patch that:
- copies the original template to the stack to be able to log it in case 
  mkstemp clears it
- on failure, logs the modified template, if any, or the original one
- logs the CWD when the template is relative
- adds a test testing this gives sane output (and doesn't crash, etc)

Signed-off-by: Arnout Engelen <arnouten@bzzt.net>

---
 Makefile          |    1 +
 t/t0007-mktemp.sh |   16 ++++++++++++++++
 test-mktemp.c     |   25 +++++++++++++++++++++++++
 wrapper.c         |   30 ++++++++++++++++++++++++++----
 4 files changed, 68 insertions(+), 4 deletions(-)
 create mode 100755 t/t0007-mktemp.sh
 create mode 100644 test-mktemp.c

diff --git a/Makefile b/Makefile
index 1f1ce04..30aafa2 100644
--- a/Makefile
+++ b/Makefile
@@ -428,6 +428,7 @@ TEST_PROGRAMS_NEED_X += test-string-pool
 TEST_PROGRAMS_NEED_X += test-svn-fe
 TEST_PROGRAMS_NEED_X += test-treap
 TEST_PROGRAMS_NEED_X += test-index-version
+TEST_PROGRAMS_NEED_X += test-mktemp
 
 TEST_PROGRAMS = $(patsubst %,%$X,$(TEST_PROGRAMS_NEED_X))
 
diff --git a/t/t0007-mktemp.sh b/t/t0007-mktemp.sh
new file mode 100755
index 0000000..7abeeca
--- /dev/null
+++ b/t/t0007-mktemp.sh
@@ -0,0 +1,16 @@
+#!/bin/sh
+
+test_description='test creating temporary files'
+. ./test-lib.sh
+
+check_errormsg() {
+	test_expect_success "$1" "
+		test-mktemp $2 &>actual
+		grep \"$3\" actual
+		"
+}
+
+check_errormsg "Creating temporary file in nonexisting directory" n "Unable to create temporary file '/tmp/does/not/exist/test"
+check_errormsg "Creating temporary file in invalid relative directory" p "at /"
+
+test_done
diff --git a/test-mktemp.c b/test-mktemp.c
new file mode 100644
index 0000000..fad2908
--- /dev/null
+++ b/test-mktemp.c
@@ -0,0 +1,25 @@
+/*
+ * test-mktemp.c: code to exercise the creation of temporary files
+ */
+#include "wrapper.h"
+
+int main(int argc, char *argv[])
+{
+	if (argc != 2) {
+		fprintf(stderr, "Expected 1 parameter defining the situation to test");
+		exit(-1);
+	}
+	switch (argv[1][0]) {
+		case 'n':
+			// temporary file in nonexistent directory
+			xmkstemp(strdup("/tmp/does/not/exist/testXXXXXX"));
+			break;
+		case 'p':
+			// temporary file in directory where we have no write permissions
+			xmkstemp(strdup("../../foo/testXXXXXX"));
+			break;
+		default:
+			fprintf(stderr, "No such test case: %s\n", argv[0]);
+	}
+	return 0;
+}
diff --git a/wrapper.c b/wrapper.c
index fd8ead3..b588e67 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -212,20 +212,42 @@ FILE *xfdopen(int fd, const char *mode)
 int xmkstemp(char *template)
 {
 	int fd;
+	char originalTemplate[255];
+	strncpy(originalTemplate, template, 255);
+	originalTemplate[254] = '\0';
 
 	fd = mkstemp(template);
-	if (fd < 0)
-		die_errno("Unable to create temporary file");
+	if (fd < 0) {
+		if (strlen(template) == 0) {
+			template = originalTemplate;
+		}
+		if (*template == '/') {
+			die_errno("Unable to create temporary file '%s'", template);
+		} else {
+			die_errno("Unable to create temporary file '%s' at %s", template, getcwd(NULL, 0));
+		}
+	}
 	return fd;
 }
 
 int xmkstemp_mode(char *template, int mode)
 {
 	int fd;
+	char originalTemplate[255];
+	strncpy(originalTemplate, template, 255);
+	originalTemplate[254] = '\0';
 
 	fd = git_mkstemp_mode(template, mode);
-	if (fd < 0)
-		die_errno("Unable to create temporary file");
+	if (fd < 0) {
+		if (strlen(template) == 0) {
+			template = originalTemplate;
+		}
+		if (*template == '/') {
+			die_errno("Unable to create temporary file '%s'", template);
+		} else {
+			die_errno("Unable to create temporary file '%s' at %s", template, getcwd(NULL, 0));
+		}
+	}
 	return fd;
 }
 
-- 
1.7.2.3

Re: [PATCH] log which temporary file could not be created

[Arnout Engelen]

Thanks for your feedback. 

Modified patch all the way below ;)

On Thu, Oct 21, 2010 at 03:58:00PM -0500, Jonathan Nieder wrote:
> A strdup() takes much more than a strncpy() last time I checked.  So I'm
> glad to see you're using the latter. :)

:)

> Is exit(-1) portable?  I'd suggest using die() or usage().

I think it is, but 'usage' is indeed neater. Done.

> > +			// temporary file in nonexistent directory
> // does not work on C89-based compilers (sadly, there are still many
> in wide use).  

Changed to /* */

> > +			xmkstemp(strdup("/tmp/does/not/exist/testXXXXXX"));
> 
> Probably better to take a parameter with the filename.

Done

> > +++ b/t/t0007-mktemp.sh
> > +		test-mktemp $2 &>actual
> 
> &> does not work on most shells.

Changed to '2>', tested with zsh, ksh and bash.

> Might be clearer to spell these out:
> 
>  test_expect_success 'mktemp to nonexistent directory prints filename' '
> 	test_must_fail test-mktemp doesnotexist/testXXXXXX 2>err &&
> 	grep "doesnotexist/test" err
>  '
> 
>  test_expect_success POSIXPERM 'mktemp to unwritable directory prints filename' '
> 	mkdir cannotwrite &&
> 	chmod -w cannotwrite &&
> 	test_when_finished "chmod +w cannotwrite" &&
> 	test_must_fail test-mktemp cannotwrite/testXXXXXX 2>err &&
> 	grep "cannotwrite/test" err
>  '
> 
> This probably would belong in t0070-fundamental.sh.

Done and moved

> > --- a/wrapper.c
> > +++ b/wrapper.c
> > @@ -212,20 +212,42 @@ FILE *xfdopen(int fd, const char *mode)
> >  int xmkstemp(char *template)
> >  {
> >  	int fd;
> > +	char originalTemplate[255];
> 
> The existing convention is to use lowercase, brief names, with
> underscores separating words where appropraite.  See "Chapter 4:
> Naming" from Documentation/CodingStyle in linux-2.6 for explanation.

Changed to 'origtemplate'

> > +	strncpy(originalTemplate, template, 255);
> > +	originalTemplate[254] = '\0';
> 
> Maybe strlcpy() would be simpler?

Jep, thanks, didn't know that one. Changed.

> >  	fd = mkstemp(template);
> > -	if (fd < 0)
> > -		die_errno("Unable to create temporary file");
> > +	if (fd < 0) {
> > +		if (strlen(template) == 0) {
> > +			template = originalTemplate;
> > +		}
> 
> Useless use of strlen().  You probably wanted 'if (!template[0])'.

I thought strlen() would be a bit neater/more readable - but changed.

> Unnecessary brace clutter (see Documentation/CodingGuidelines for
> explanation).

Changed

> > +		if (*template == '/') {
> > +			die_errno("Unable to create temporary file '%s'", template);
> > +		} else {
> > +			die_errno("Unable to create temporary file '%s' at %s", template, getcwd(NULL, 0));
> 
> Okay.  is_absolute_path() might be helpful on Windows.

Changed.

Verified the testcases still succeed. 

The patch below:
- copies the original template to the stack, to be able to log it in case
  mkstemp clears it
- on failure, logs the modified template, if any, or the original one
- logs the CWD when the template is relative
- adds a test testing this gives sane output (and doesn't crash, etc)

Signed-off-by: Arnout Engelen <arnouten@bzzt.net>
---
 Makefile               |    1 +
 t/t0070-fundamental.sh |   13 +++++++++++++
 test-mktemp.c          |   14 ++++++++++++++
 wrapper.c              |   26 ++++++++++++++++++++++----
 4 files changed, 50 insertions(+), 4 deletions(-)
 create mode 100644 test-mktemp.c

diff --git a/Makefile b/Makefile
index 1f1ce04..30aafa2 100644
--- a/Makefile
+++ b/Makefile
@@ -428,6 +428,7 @@ TEST_PROGRAMS_NEED_X += test-string-pool
 TEST_PROGRAMS_NEED_X += test-svn-fe
 TEST_PROGRAMS_NEED_X += test-treap
 TEST_PROGRAMS_NEED_X += test-index-version
+TEST_PROGRAMS_NEED_X += test-mktemp
 
 TEST_PROGRAMS = $(patsubst %,%$X,$(TEST_PROGRAMS_NEED_X))
 
diff --git a/t/t0070-fundamental.sh b/t/t0070-fundamental.sh
index 680d7d6..9bee8bf 100755
--- a/t/t0070-fundamental.sh
+++ b/t/t0070-fundamental.sh
@@ -12,4 +12,17 @@ test_expect_success 'character classes (isspace, isalpha etc.)' '
 	test-ctype
 '
 
+test_expect_success 'mktemp to nonexistent directory prints filename' '
+	test_must_fail test-mktemp doesnotexist/testXXXXXX 2>err &&
+	grep "doesnotexist/test" err
+'
+
+test_expect_success POSIXPERM 'mktemp to unwritable directory prints filename' '
+	mkdir cannotwrite &&
+	chmod -w cannotwrite &&
+	test_when_finished "chmod +w cannotwrite" &&
+	test_must_fail test-mktemp cannotwrite/testXXXXXX 2>err &&
+	grep "cannotwrite/test" err
+'
+
 test_done
diff --git a/test-mktemp.c b/test-mktemp.c
new file mode 100644
index 0000000..30e266a
--- /dev/null
+++ b/test-mktemp.c
@@ -0,0 +1,14 @@
+/*
+ * test-mktemp.c: code to exercise the creation of temporary files
+ */
+#include "wrapper.h"
+
+int main(int argc, char *argv[])
+{
+	if (argc != 2) {
+		usage("Expected 1 parameter defining the temporary file template");
+	}
+	xmkstemp(strdup(argv[1]));
+
+	return 0;
+}
diff --git a/wrapper.c b/wrapper.c
index fd8ead3..b5f10d1 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -212,20 +212,38 @@ FILE *xfdopen(int fd, const char *mode)
 int xmkstemp(char *template)
 {
 	int fd;
+	char origtemplate[255];
+	strlcpy(origtemplate, template, 255);
 
 	fd = mkstemp(template);
-	if (fd < 0)
-		die_errno("Unable to create temporary file");
+	if (fd < 0) {
+		if (!template[0])
+			template = origtemplate;
+
+		if (is_absolute_path(template))
+			die_errno("Unable to create temporary file '%s'", template);
+		else
+			die_errno("Unable to create temporary file '%s' at %s", template, getcwd(NULL, 0));
+	}
 	return fd;
 }
 
 int xmkstemp_mode(char *template, int mode)
 {
 	int fd;
+	char origtemplate[255];
+	strlcpy(origtemplate, template, 255);
 
 	fd = git_mkstemp_mode(template, mode);
-	if (fd < 0)
-		die_errno("Unable to create temporary file");
+	if (fd < 0) {
+		if (!template[0])
+			template = origtemplate;
+
+		if (is_absolute_path(template))
+			die_errno("Unable to create temporary file '%s'", template);
+		else
+			die_errno("Unable to create temporary file '%s' at %s", template, getcwd(NULL, 0));
+	}
 	return fd;
 }
 
-- 
1.7.2.3