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[PATCH v2 09/12] attr: (re)introduce git_check_attr() and struct git_attr_check

From
Junio C Hamano <gitster@pobox.com>
Date
May 16, 2016, 21:05 UTC
Message-ID
<20160516210545.6591-10-gitster@pobox.com>
In-Reply-To
<20160516210545.6591-1-gitster@pobox.com>
A common pattern to check N attributes for many paths is to
 (1) prepare an array A of N git_attr_check_elem items;
 (2) call git_attr() to intern the N attribute names and fill A;
 (3) repeatedly call git_check_attrs() for path with N and A;

A look-up for these N attributes for a single path P scans the entire attr_stack, starting from the .git/info/attributes file and then .gitattributes file in the directory the path P is in, going upwards to find .gitattributes file found in parent directories.

An earlier commit 06a604e6 (attr: avoid heavy work when we know the specified attr is not defined, 2014-12-28) tried to optimize out this scanning for one trivial special case: when the attribute being sought is known not to exist, we do not have to scan for it. While this may be a cheap and effective heuristic, it would not work well when N is (much) more than 1.

What we would want is a more customized way to skip irrelevant entries in the attribute stack, and the definition of irrelevance is tied to the set of attributes passed to git_check_attrs() call, i.e. the set of attributes being sought. The data necessary for this optimization needs to live alongside the set of attributes, but a simple array of git_attr_check_elem simply does not have any place for that.

Introduce "struct git_attr_check" that contains N, the number of attributes being sought, and A, the array that holds N git_attr_check_elem items, and a function git_check_attr() that takes a path P and this structure as its parameters. This structure can later be extended to hold extra data necessary for optimization.

Also, to make it easier to write the first two steps in common cases, introduce git_attr_check_initl() helper function, which takes a NULL-terminated list of attribute names and initialize this structure.

As an illustration of this new API, convert archive.c that asks for export-subst and export-ignore attributes for each paths.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 archive.c | 24 ++++++------------------
 attr.c    | 34 ++++++++++++++++++++++++++++++++++
 attr.h    |  9 +++++++++
 3 files changed, 49 insertions(+), 18 deletions(-)
diff --git a/archive.c b/archive.c
index 0f6acc5..7779af1 100644
--- a/archive.c
+++ b/archive.c
@@ -87,19 +87,6 @@ void *sha1_file_to_archive(const struct archiver_args *args,
 	return buffer;
 }
 
-static void setup_archive_check(struct git_attr_check_elem *check)
-{
-	static struct git_attr *attr_export_ignore;
-	static struct git_attr *attr_export_subst;
-
-	if (!attr_export_ignore) {
-		attr_export_ignore = git_attr("export-ignore");
-		attr_export_subst = git_attr("export-subst");
-	}
-	check[0].attr = attr_export_ignore;
-	check[1].attr = attr_export_subst;
-}
-
 struct directory {
 	struct directory *up;
 	struct object_id oid;
@@ -123,7 +110,7 @@ static int write_archive_entry(const unsigned char *sha1, const char *base,
 	struct archiver_context *c = context;
 	struct archiver_args *args = c->args;
 	write_archive_entry_fn_t write_entry = c->write_entry;
-	struct git_attr_check_elem check[2];
+	static struct git_attr_check *check;
 	const char *path_without_prefix;
 	int err;
 
@@ -137,11 +124,12 @@ static int write_archive_entry(const unsigned char *sha1, const char *base,
 		strbuf_addch(&path, '/');
 	path_without_prefix = path.buf + args->baselen;
 
-	setup_archive_check(check);
-	if (!git_check_attrs(path_without_prefix, ARRAY_SIZE(check), check)) {
-		if (ATTR_TRUE(check[0].value))
+	if (!check)
+		check = git_attr_check_initl("export-ignore", "export-subst", NULL);
+	if (!git_check_attr(path_without_prefix, check)) {
+		if (ATTR_TRUE(check->check[0].value))
 			return 0;
-		args->convert = ATTR_TRUE(check[1].value);
+		args->convert = ATTR_TRUE(check->check[1].value);
 	}
 
 	if (S_ISDIR(mode) || S_ISGITLINK(mode)) {
diff --git a/attr.c b/attr.c
index 8aa346c..285fc58 100644
--- a/attr.c
+++ b/attr.c
@@ -825,3 +825,37 @@ void git_attr_set_direction(enum git_attr_direction new, struct index_state *ist
 		drop_attr_stack();
 	use_index = istate;
 }
+
+int git_check_attr(const char *path, struct git_attr_check *check)
+{
+	return git_check_attrs(path, check->check_nr, check->check);
+}
+
+struct git_attr_check *git_attr_check_initl(const char *one, ...)
+{
+	struct git_attr_check *check;
+	int cnt;
+	va_list params;
+	const char *param;
+
+	va_start(params, one);
+	for (cnt = 1; (param = va_arg(params, const char *)) != NULL; cnt++)
+		;
+	va_end(params);
+	check = xcalloc(1,
+			sizeof(*check) + cnt * sizeof(*(check->check)));
+	check->check_nr = cnt;
+	check->check = (struct git_attr_check_elem *)(check + 1);
+
+	check->check[0].attr = git_attr(one);
+	va_start(params, one);
+	for (cnt = 1; cnt < check->check_nr; cnt++) {
+		param = va_arg(params, const char *);
+		if (!param)
+			die("BUG: counted %d != ended at %d",
+			    check->check_nr, cnt);
+		check->check[cnt].attr = git_attr(param);
+	}
+	va_end(params);
+	return check;
+}
diff --git a/attr.h b/attr.h
index cab82ec..3ed89e5 100644
--- a/attr.h
+++ b/attr.h
@@ -29,6 +29,15 @@ struct git_attr_check_elem {
 	const char *value;
 };
 
+struct git_attr_check {
+	int check_nr;
+	int check_alloc;
+	struct git_attr_check_elem *check;
+};
+
+extern struct git_attr_check *git_attr_check_initl(const char *, ...);
+extern int git_check_attr(const char *path, struct git_attr_check *);
+
 /*
  * Return the name of the attribute represented by the argument.  The
  * return value is a pointer to a null-delimited string that is part

-- 
2.8.2-748-gfb85f76
Previous: Junio C HamanoNext: Eric Sunshine
Message 17 of 27 in “revamping git_check_attr() API”
  1. 00/12 revamping git_check_attr() APIJunio C Hamano, May 16, 2016
  2. 01/12 commit.c: use strchrnul() to scan for one lineJunio C Hamano, May 16, 2016
  3. Stefan BellerMay 16, 2016
  4. Junio C HamanoMay 16, 2016
  5. Stefan BellerMay 16, 2016
  6. 02/12 attr.c: use strchrnul() to scan for one lineJunio C Hamano, May 16, 2016
  7. Stefan BellerMay 16, 2016
  8. Junio C HamanoMay 16, 2016
  9. 03/12 attr.c: update a stale comment on "struct match_attr"Junio C Hamano, May 16, 2016
  10. Stefan BellerMay 16, 2016
  11. Junio C HamanoMay 16, 2016
  12. 04/12 attr.c: explain the lack of attr-name syntax check in parse_attr()Junio C Hamano, May 16, 2016
  13. 05/12 attr.c: complete a sentence in a commentJunio C Hamano, May 16, 2016
  14. 06/12 attr.c: mark where #if DEBUG ends more clearlyJunio C Hamano, May 16, 2016
  15. 07/12 attr.c: simplify macroexpand_one()Junio C Hamano, May 16, 2016
  16. 08/12 attr: rename function and struct related to checking attributesJunio C Hamano, May 16, 2016
  17. 09/12 attr: (re)introduce git_check_attr() and struct git_attr_checkJunio C Hamano, May 16, 2016
  18. Eric SunshineMay 17, 2016
  19. Junio C HamanoMay 17, 2016
  20. 10/12 attr: convert git_all_attrs() to use "struct git_attr_check"Junio C Hamano, May 16, 2016
  21. Junio C HamanoMay 17, 2016
  22. Junio C HamanoMay 17, 2016
  23. Stefan BellerMay 18, 2016
  24. 11/12 attr: convert git_check_attrs() callers to use the new APIJunio C Hamano, May 16, 2016
  25. 12/12 attr: retire git_check_attrs() APIJunio C Hamano, May 16, 2016
  26. Stefan BellerMay 18, 2016
  27. Junio C HamanoMay 18, 2016

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