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Re: [RFC PATCHv6 1/2] repack: rewrite the shell script in C

From
Stefan Beller <stefanbeller@googlemail.com>
Date
Aug 21, 2013, 22:15 UTC
Message-ID
<52153C01.6040101@googlemail.com>
In-Reply-To
<xmqqfvu2u5io.fsf@gitster.dls.corp.google.com>
On 08/21/2013 10:56 PM, Junio C Hamano wrote:
Show 36 quoted lines
> Stefan Beller <stefanbeller@googlemail.com> writes:
> 
>> The motivation of this patch is to get closer to a goal of being
>> able to have a core subset of git functionality built in to git.
>> That would mean
>>
>>  * people on Windows could get a copy of at least the core parts
>>    of Git without having to install a Unix-style shell
>>
>>  * people deploying to servers don't have to rewrite the #! line
>>    or worry about the PATH and quality of installed POSIX
>>    utilities, if they are only using the built-in part written
>>    in C
> 
> I am not sure what is meant by the latter.  Rewriting #! is part of
> any scripted Porcelain done by the top-level Makefile, and I do not
> think we have seen any problem reports on it.
> 
> As to "quality of ... utilities", I think the real issue some people
> in the thread had was not about "deploying to servers" but about
> installing in a minimalistic chrooted environment where standard
> tools may be lacking.
> 
>> diff --git a/builtin/repack.c b/builtin/repack.c
>> new file mode 100644
>> index 0000000..fb050c0
>> --- /dev/null
>> +++ b/builtin/repack.c
>> @@ -0,0 +1,376 @@
>> +/*
>> + * The shell version was written by Linus Torvalds (2005) and many others.
>> + * This is a translation into C by Stefan Beller (2013)
>> + */
> 
> I am not sure if we want to record "ownership" in the code like
> this; it will go stale over time.

I'll remove it. Initially I put it there as I found similar comments in other files as well.

>> +static int delta_base_offset = 1;
>> +char *packdir;
> 
> Does this have to be global?

We could pass it to all the functions, making it not global. I'd be ok with that for the functions get_pack_filenames and remove_redundant_pack, but we also need to know packdir in remove_temporary_files which is called from the signal handler remove_pack_on_signal.

As the path is pretty obvious (get_object_directory() + "/pack"), we could however also construct it again in the signal handler.

Show 7 quoted lines
> So in summary:
> 
> 	dir = opendir(packdir);
>         if (!dir)
> 		return;
> 
> 	strbuf_addf(&buf, "%s-", packtmp);

packtmp is not yet a global variable, but could be passed to to this function. Currently we're reconstructing it here.

Show 8 quoted lines
> 
>         /* Point at the slash at the end of ".../objects/pack/" */
> 	dirlen = strlen(packdir) + 1;
>         /* Point at the dash at the end of ".../.tmp-%d-pack-" */
>         prefixlen = buf.len - dirlen;
> 
> You would need to move the initialization of packdir and packtmp
> before sigchain_push() in cmd_repack() if you were to do this.
Ah ok, I'll do so.
Show 5 quoted lines
>> +
>> +		if (!file_exists(mkpath("%s/%s.keep", packdir, fname)))
>> +			string_list_append_nodup(fname_list, fname);
> 
> mental note: this is getting names of non-kept packs, not all packs.
I should document that. ;)
Show 6 quoted lines
>> +	while (strbuf_getline(&line, out, '\n') != EOF) {
>> +		if (line.len != 40)
>> +			die("repack: Expecting 40 character sha1 lines only from pack-objects.");
>> +		strbuf_addstr(&line, "");
> 
> What is this addstr() about?

According to the documentation of strbufs, we cannot assume to have sane strings, but anything. Adding an empty string however will make sure to add a NUL-terminated string to the buffer, no?

In a previous roll of this patch, which operated on char* line, there was just line[40] = '\0'; // replacing '\n' by '\0' to have it sane in the string list.

Show 8 quoted lines
> 
>> +		string_list_append(&names, line.buf);
>> +		count_packs++;
> 
> It probably is more in line with our naming convention to call this
> nr_packs, num_packs, etc.  "count_packs" sounds more like a boolean
> that instructs the code to either count or not bother counting,
> which this thing is not.

This is something subtle, but important to know. Thanks, will be fixed in the reroll.

Show 8 quoted lines
>> +
>> +			if (rename(fname, fname_old)) {
>> +				failed = 1;
>> +				break;
> 
> "break"-ing from here leaks fname_old.  As the only out-of-line call
> file_exists() is just a thin wrapper around lstat(), I think it is
> fine not to pathdup the fname_old here.
fixed

I'd really appreciate, if there was documentation on these functions. (When is mkpath safe? What is better in which situation: mkpath or strbufs?) Maybe I could start doing it (but only those functions I used so far, there are many more in cache.h)

Show 11 quoted lines
> 
>> +			}
>> +			string_list_append_nodup(&rollback, fname);
>> +			free(fname);
> 
> This looks bad, doesn't it?  append_nodup() lets &rollback string
> list to take the ownership of the piece of memory pointed at by
> fname, but then you free it here, no?
> 
> If you initialize &rollback with INIT_NODUP, you would not have to
> call append_nodup().

Removed the free. Having rollback initialized with NODUP and then not explicitely using append_nodup() makes me feel unhappy, because now you need to check different places to make sure there is no leaking memory, (you need to know the list is NODUP). I changed it nevertheless, maybe I feel enlightened later on. ;)

As Matthieu proposed, I also set CFLAGS += -Wdeclaration-after-statement in config.mak now. Hopefully I don't screw up again now.

Thanks, Stefan

--8<--
From 79945f5ae45f08fa2dbabfa1f6b7cd0b344ec0b3 Mon Sep 17 00:00:00 2001
From: Stefan Beller <stefanbeller@googlemail.com>
Date: Thu, 22 Aug 2013 00:13:35 +0200
Subject: [PATCH] Suggestions by Junio
---
 builtin/repack.c | 68 ++++++++++++++++++++++++++------------------------------
 1 file changed, 31 insertions(+), 37 deletions(-)
diff --git a/builtin/repack.c b/builtin/repack.c
index 1f13e0d..bb90f07 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -1,8 +1,3 @@
-/*
- * The shell version was written by Linus Torvalds (2005) and many others.
- * This is a translation into C by Stefan Beller (2013)
- */
-
 #include "builtin.h"
 #include "cache.h"
 #include "dir.h"
@@ -13,9 +8,8 @@
 #include "string-list.h"
 #include "argv-array.h"
 
-/* enabled by default since 22c79eab (2008-06-25) */
 static int delta_base_offset = 1;
-char *packdir;
+char *packdir, *packtmp;
 
 static const char *const git_repack_usage[] = {
 	N_("git repack [options]"),
@@ -41,18 +35,16 @@ static void remove_temporary_files(void)
 	DIR *dir;
 	struct dirent *e;
 
-	/* .git/objects/pack */
-	strbuf_addstr(&buf, get_object_directory());
-	strbuf_addstr(&buf, "/pack");
-	dir = opendir(buf.buf);
-	if (!dir) {
-		strbuf_release(&buf);
+	dir = opendir(packdir);
+	if (!dir)
 		return;
-	}
 
-	/* .git/objects/pack/.tmp-$$-pack-* */
+	strbuf_addstr(&buf, packdir);
+
+	/* dirlen holds the length of the path before the file name */
 	dirlen = buf.len + 1;
-	strbuf_addf(&buf, "/.tmp-%d-pack-", (int)getpid());
+	strbuf_addf(&buf, "%s", packtmp);
+	/* prefixlen holds the length of the prefix */
 	prefixlen = buf.len - dirlen;
 
 	while ((e = readdir(dir))) {
@@ -73,11 +65,16 @@ static void remove_pack_on_signal(int signo)
 	raise(signo);
 }
 
+/*
+ * Adds all packs hex strings to the fname list, which do not
+ * have a corresponding .keep file.
+ */
 static void get_pack_filenames(struct string_list *fname_list)
 {
 	DIR *dir;
 	struct dirent *e;
 	char *fname;
+	size_t len;
 
 	if (!(dir = opendir(packdir)))
 		return;
@@ -86,7 +83,7 @@ static void get_pack_filenames(struct string_list *fname_list)
 		if (suffixcmp(e->d_name, ".pack"))
 			continue;
 
-		size_t len = strlen(e->d_name) - strlen(".pack");
+		len = strlen(e->d_name) - strlen(".pack");
 		fname = xmemdupz(e->d_name, len);
 
 		if (!file_exists(mkpath("%s/%s.keep", packdir, fname)))
@@ -95,14 +92,14 @@ static void get_pack_filenames(struct string_list *fname_list)
 	closedir(dir);
 }
 
-static void remove_redundant_pack(const char *path, const char *sha1)
+static void remove_redundant_pack(const char *path_prefix, const char *hex)
 {
 	const char *exts[] = {".pack", ".idx", ".keep"};
 	int i;
 	struct strbuf buf = STRBUF_INIT;
 	size_t plen;
 
-	strbuf_addf(&buf, "%s/%s", path, sha1);
+	strbuf_addf(&buf, "%s/%s", path_prefix, hex);
 	plen = buf.len;
 
 	for (i = 0; i < ARRAY_SIZE(exts); i++) {
@@ -115,15 +112,14 @@ static void remove_redundant_pack(const char *path, const char *sha1)
 int cmd_repack(int argc, const char **argv, const char *prefix)
 {
 	const char *exts[2] = {".idx", ".pack"};
-	char *packtmp;
 	struct child_process cmd;
 	struct string_list_item *item;
 	struct argv_array cmd_args = ARGV_ARRAY_INIT;
 	struct string_list names = STRING_LIST_INIT_DUP;
-	struct string_list rollback = STRING_LIST_INIT_DUP;
+	struct string_list rollback = STRING_LIST_INIT_NODUP;
 	struct string_list existing_packs = STRING_LIST_INIT_DUP;
 	struct strbuf line = STRBUF_INIT;
-	int count_packs, ext, ret;
+	int nr_packs, ext, ret, failed;
 	FILE *out;
 
 	/* variables to be filled by option parsing */
@@ -173,11 +169,11 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 	argc = parse_options(argc, argv, prefix, builtin_repack_options,
 				git_repack_usage, 0);
 
-	sigchain_push_common(remove_pack_on_signal);
-
 	packdir = mkpathdup("%s/pack", get_object_directory());
 	packtmp = mkpathdup("%s/.tmp-%d-pack", packdir, (int)getpid());
 
+	sigchain_push_common(remove_pack_on_signal);
+
 	argv_array_push(&cmd_args, "pack-objects");
 	argv_array_push(&cmd_args, "--keep-true-parents");
 	argv_array_push(&cmd_args, "--honor-pack-keep");
@@ -233,14 +229,14 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 	if (ret)
 		return ret;
 
-	count_packs = 0;
+	nr_packs = 0;
 	out = xfdopen(cmd.out, "r");
 	while (strbuf_getline(&line, out, '\n') != EOF) {
 		if (line.len != 40)
 			die("repack: Expecting 40 character sha1 lines only from pack-objects.");
 		strbuf_addstr(&line, "");
 		string_list_append(&names, line.buf);
-		count_packs++;
+		nr_packs++;
 	}
 	fclose(out);
 	ret = finish_command(&cmd);
@@ -248,10 +244,10 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 		return ret;
 	argv_array_clear(&cmd_args);
 
-	if (!count_packs && !quiet)
+	if (!nr_packs && !quiet)
 		printf("Nothing new to pack.\n");
 
-	int failed = 0;
+	failed = 0;
 	for_each_string_list_item(item, &names) {
 		for (ext = 0; ext < 2; ext++) {
 			char *fname, *fname_old;
@@ -262,7 +258,7 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 				continue;
 			}
 
-			fname_old = mkpathdup("%s/old-%s%s", packdir,
+			fname_old = mkpath("%s/old-%s%s", packdir,
 						item->string, exts[ext]);
 			if (file_exists(fname_old))
 				unlink(fname_old);
@@ -271,15 +267,13 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 				failed = 1;
 				break;
 			}
-			string_list_append_nodup(&rollback, fname);
-			free(fname);
-			free(fname_old);
+			string_list_append(&rollback, fname);
 		}
 		if (failed)
 			break;
 	}
 	if (failed) {
-		struct string_list rollback_failure;
+		struct string_list rollback_failure = STRING_LIST_INIT_DUP;
 		for_each_string_list_item(item, &rollback) {
 			char *fname, *fname_old;
 			fname = mkpathdup("%s/%s", packdir, item->string);
@@ -289,7 +283,7 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 			free(fname);
 		}
 
-		if (rollback.nr) {
+		if (rollback_failure.nr) {
 			int i;
 			fprintf(stderr,
 				"WARNING: Some packs in use have been renamed by\n"
@@ -299,10 +293,10 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 				"WARNING: attempt to rename them back to their\n"
 				"WARNING: original names also failed.\n"
 				"WARNING: Please rename them in %s manually:\n", packdir);
-			for (i = 0; i < rollback.nr; i++)
+			for (i = 0; i < rollback_failure.nr; i++)
 				fprintf(stderr, "WARNING:   old-%s -> %s\n",
-					rollback.items[i].string,
-					rollback.items[i].string);
+					rollback_failure.items[i].string,
+					rollback_failure.items[i].string);
 		}
 		exit(1);
 	}

-- 
1.8.4.rc3.1.gc1ebd90
Previous: Matthieu MoyNext: Junio C Hamano
Message 37 of 72 in “Rewriting git-repack in C”
  1. Rewriting git-repack in CStefan Beller, Aug 13, 2013
  2. repack: rewrite the shell script in C.Stefan Beller, Aug 13, 2013
  3. Matthieu MoyAug 14, 2013
  4. Stefan BellerAug 14, 2013
  5. repack: rewrite the shell script in C.Stefan Beller, Aug 14, 2013
  6. Antoine PelisseAug 14, 2013
  7. Stefan BellerAug 14, 2013
  8. Jeff KingAug 14, 2013
  9. Martin FickAug 14, 2013
  10. Stefan BellerAug 14, 2013
  11. Martin FickAug 14, 2013
  12. Junio C HamanoAug 14, 2013
  13. Martin FickAug 14, 2013
  14. Junio C HamanoAug 15, 2013
  15. [RFC PATCHv2] repack: rewrite the shell script in C.Stefan Beller, Aug 16, 2013
  16. René ScharfeAug 17, 2013
  17. Kyle J. McKayAug 17, 2013
  18. Stefan BellerAug 18, 2013
  19. [RFC PATCHv3] repack: rewrite the shell script in C.Stefan Beller, Aug 18, 2013
  20. Kyle J. McKayAug 18, 2013
  21. René ScharfeAug 18, 2013
  22. [RFC PATCHv4] repack: rewrite the shell script in C.Stefan Beller, Aug 18, 2013
  23. [RFC PATCHv4] repack: rewrite the shell script in C.Stefan Beller, Aug 19, 2013
  24. Johannes SixtAug 20, 2013
  25. Stefan BellerAug 20, 2013
  26. Johannes SixtAug 20, 2013
  27. René ScharfeAug 20, 2013
  28. Stefan BellerAug 20, 2013
  29. repack: rewrite the shell script in C.Stefan Beller, Aug 20, 2013
  30. Jonathan NiederAug 21, 2013
  31. Stefan BellerAug 21, 2013
  32. Stefan BellerAug 21, 2013
  33. 1/2 repack: rewrite the shell script in CStefan Beller, Aug 21, 2013
  34. 2/2 repack: retain the return value of pack-objectsStefan Beller, Aug 21, 2013
  35. Junio C HamanoAug 21, 2013
  36. Matthieu MoyAug 21, 2013
  37. Stefan BellerAug 21, 2013
  38. Junio C HamanoAug 21, 2013
  39. Stefan BellerAug 21, 2013
  40. Johannes SixtAug 22, 2013
  41. Jonathan NiederAug 22, 2013
  42. Matthieu MoyAug 21, 2013
  43. Stefan BellerAug 21, 2013
  44. Matthieu MoyAug 21, 2013
  45. Stefan BellerAug 21, 2013
  46. Matthieu MoyAug 21, 2013
  47. Johannes SixtAug 22, 2013
  48. Johannes SixtAug 22, 2013
  49. repack: rewrite the shell script in C (squashing proposal)Stefan Beller, Aug 22, 2013
  50. Junio C HamanoAug 22, 2013
  51. Jonathan NiederAug 20, 2013
  52. Johannes SixtAug 21, 2013
  53. Stefan BellerAug 20, 2013
  54. Jonathan NiederAug 20, 2013
  55. Dokumenting api-paths.txtStefan Beller, Aug 20, 2013
  56. Jonathan NiederAug 20, 2013
  57. Stefan BellerAug 21, 2013
  58. Junio C HamanoAug 22, 2013
  59. Junio C HamanoAug 14, 2013
  60. Matthieu MoyAug 14, 2013
  61. Stefan BellerAug 15, 2013
  62. Duy NguyenAug 15, 2013
  63. Junio C HamanoAug 14, 2013
  64. Matthieu MoyAug 14, 2013
  65. Martin FickAug 14, 2013
  66. Martin FickAug 15, 2013
  67. Stefan BellerAug 15, 2013
  68. Martin FickAug 15, 2013
  69. Duy NguyenAug 15, 2013
  70. Junio C HamanoAug 14, 2013
  71. Stefan BellerAug 15, 2013
  72. Matthieu MoyAug 14, 2013

Read the whole thread, see it on lore, or plain text.

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