[PATCH 2/2] optimize set_shared_perm()

[PATCH 2/2] optimize set_shared_perm()

[Torsten Bögershausen]

  optimize set_shared_perm() in path.c:

  - sometimes the chown() function is called even when not needed.
    (This can be provoced by running t1301, and adding some debug code)

    Save a chmod from 400 to 400, or from 600->600 on these files:
    .git/info/refs+
    .git/objects/info/packs+

    Save chmod on directories from 2770 to 2770:
    .git/refs
    .git/refs/heads
    .git/refs/tags

  - as all callers use mode == 0 when caling set_shared_perm(),
    the function can be simplified.
  - all callers use the macro adjust_shared_perm(path) from cache.h
    Convert adjust_shared_perm() from a macro into a function prototype

Signed-off-by: Torsten Bögershausen <tboegi@web.de>
---
 cache.h |  3 +--
 path.c  | 71 +++++++++++++++++++++++++++++++++++------------------------------
 2 files changed, 39 insertions(+), 35 deletions(-)

diff --git a/cache.h b/cache.h
index 59e5b53..65a9db7 100644
--- a/cache.h
+++ b/cache.h
@@ -727,8 +727,7 @@ enum sharedrepo {
 	PERM_EVERYBODY      = 0664
 };
 int git_config_perm(const char *var, const char *value);
-int set_shared_perm(const char *path, int mode);
-#define adjust_shared_perm(path) set_shared_perm((path), 0)
+int adjust_shared_perm(const char *path);
 int safe_create_leading_directories(char *path);
 int safe_create_leading_directories_const(const char *path);
 int mkdir_in_gitdir(const char *path);
diff --git a/path.c b/path.c
index 2fdccc2..4bc918a 100644
--- a/path.c
+++ b/path.c
@@ -1,14 +1,5 @@
 /*
- * I'm tired of doing "vsnprintf()" etc just to open a
- * file, so here's a "return static buffer with printf"
- * interface for paths.
- *
- * It's obviously not thread-safe. Sue me. But it's quite
- * useful for doing things like
- *
- *   f = open(mkpath("%s/%s.git", base, name), O_RDONLY);
- *
- * which is what it's designed for.
+ * Different utilitiy functions for path and path names
  */
 #include "cache.h"
 #include "strbuf.h"
@@ -105,6 +96,13 @@ char *git_pathdup(const char *fmt, ...)
 	return xstrdup(ret);
 }
 
+/*
+ * I'm tired of doing "vsnprintf()" etc just to open a
+ * file, so here's an interface for paths.
+ *
+ * f = open(mkpath("%s/%s.git", base, name), O_RDONLY);
+ *
+ */
 char *mkpathdup(const char *fmt, ...)
 {
 	char *path;
@@ -405,22 +403,13 @@ const char *enter_repo(const char *path, int strict)
 	return NULL;
 }
 
-int set_shared_perm(const char *path, int mode)
+static int calc_shared_perm(int mode)
 {
-	int tweak, shared, orig_mode;
+	int tweak, shared;
 
-	if (!shared_repository) {
-		if (mode)
-			return chmod(path, mode & ~S_IFMT);
-		return 0;
-	}
-	if (!mode) {
-		if (get_st_mode_bits(path, &mode) < 0)
-			return -1;
-		orig_mode = mode;
-	} else
-		orig_mode = 0;
-	if (shared_repository < 0)
+	if (!shared_repository)
+		return mode;
+	else if (shared_repository < 0)
 		shared = -shared_repository;
 	else
 		shared = shared_repository;
@@ -436,16 +425,32 @@ int set_shared_perm(const char *path, int mode)
 	else
 		mode |= tweak;
 
-	if (S_ISDIR(mode)) {
-		/* Copy read bits to execute bits */
-		mode |= (shared & 0444) >> 2;
-		mode |= FORCE_DIR_SET_GID;
-	}
+	return mode;
+}
+
+static int calc_shared_perm_dir(int mode)
+{
+	mode = calc_shared_perm(mode);
+
+	/* Copy read bits to execute bits */
+	mode |= (mode & 0444) >> 2;
+	mode |= FORCE_DIR_SET_GID;
+	return mode;
+}
+
+int adjust_shared_perm(const char *path)
+{
+	int old_mode, new_mode;
+	if (get_st_mode_bits(path, &old_mode) < 0)
+		return -1;
+
+	if (S_ISDIR(old_mode))
+		new_mode = calc_shared_perm_dir(old_mode);
+	else
+		new_mode = calc_shared_perm(old_mode);
 
-	if (((shared_repository < 0
-	      ? (orig_mode & (FORCE_DIR_SET_GID | 0777))
-	      : (orig_mode & mode)) != mode) &&
-	    chmod(path, (mode & ~S_IFMT)) < 0)
+	if (((old_mode ^ new_mode) & ~S_IFMT) &&
+			chmod(path, (new_mode & ~S_IFMT)) < 0)
 		return -2;
 	return 0;
 }
-- 
1.8.2.341.g543621f

Re: [PATCH 2/2] optimize set_shared_perm()

[Junio C Hamano]

Torsten Bögershausen <tboegi@web.de> writes:

>   optimize set_shared_perm() in path.c:
>
>   - sometimes the chown() function is called even when not needed.
>     (This can be provoced by running t1301, and adding some debug code)
>
>     Save a chmod from 400 to 400, or from 600->600 on these files:
>     .git/info/refs+
>     .git/objects/info/packs+
>
>     Save chmod on directories from 2770 to 2770:
>     .git/refs
>     .git/refs/heads
>     .git/refs/tags
>
>   - as all callers use mode == 0 when caling set_shared_perm(),
>     the function can be simplified.
>   - all callers use the macro adjust_shared_perm(path) from cache.h
>     Convert adjust_shared_perm() from a macro into a function prototype

The last two points can become a separate "preparation" step.  The
result would be easier to read.

Your updated adjust_shared_perm() does not begin with:

	if (!shared_repository)
        	return 0;

as the original, but it always first calls to get_st_mode_bits()
which makes a call to lstat(2).

That smells like a huge regression for !shared_repository case,
unless you have updated the existing callers of adjust_shared_perm()
not to call it when !shared_repository.

> diff --git a/path.c b/path.c
> index 2fdccc2..4bc918a 100644
> --- a/path.c
> +++ b/path.c
> @@ -1,14 +1,5 @@
>  /*
> - * I'm tired of doing "vsnprintf()" etc just to open a
> - * file, so here's a "return static buffer with printf"
> - * interface for paths.
> - *
> - * It's obviously not thread-safe. Sue me. But it's quite
> - * useful for doing things like
> - *
> - *   f = open(mkpath("%s/%s.git", base, name), O_RDONLY);
> - *
> - * which is what it's designed for.
> + * Different utilitiy functions for path and path names
>   */

Removing the stale "I'm tired of" is good; you do not have to move
it anywhere.  A single-liner

	/* Utilities for paths and pathnames */

should suffice.

Will discard this step (but will keep PATCH 1/2).

Re: [PATCH 2/2] optimize set_shared_perm()

[Torsten Bögershausen]

On 29.03.13 22:20, Junio C Hamano wrote:
[snip]
> The last two points can become a separate "preparation" step.  The
> result would be easier to read.
> 
> Your updated adjust_shared_perm() does not begin with:
> 
> 	if (!shared_repository)
>         	return 0;
> 
> as the original, but it always first calls to get_st_mode_bits()
> which makes a call to lstat(2).
> 
> That smells like a huge regression for !shared_repository case,
> unless you have updated the existing callers of adjust_shared_perm()
> not to call it when !shared_repository.
> 
Thanks for carefull review:
The achieved effect of the code is the same,
but the developer is to blame.

I send a new patch of 2/2 in a minute, splitted into 2 commits.

Highlights of part 2:
a) move "if (!shared_repository)" to the right place
b) Simplify calc_shared_perm() even more: Remove the variable "int shared"
c) Remove calc_shared_perm_dir(), the functionality is baked into
   adjust_shared_perm()