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a33ce612b

Denys Vlasenko

2025-08-04

SUCCESS Duration: 155s

Subject

libbb: much faster concat_path_file()

Binary

No binary (build failed)

Architecture & Compiler Flags

Architecture: x86_64-linux-gnu Compiler: gcc (Ubuntu 11.4.0-1ubuntu1~22.04.3) 11.4.0

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Build Log

(log yok)

Commit Diff GitHub →

libbb/concat_path_file.c +75 -0 util-linux/lspci.c +1 -1 util-linux/lsusb.c +1 -1

libbb/concat_path_file.c+75 -0

@@ -17,6 +17,7 @@

	char* FAST_FUNC concat_path_file(const char path, const char filename)
	{
+	#if 0
	char *lc;

	if (!path)
@@ -25,4 +26,78 @@ char* FAST_FUNC concat_path_file(const char path, const char filename)
	while (*filename == '/')
	filename++;
	return xasprintf("%s%s%s", path, (lc==NULL ? "/" : ""), filename);
+	#else
+	/* ^^^^^^^^^^^ timing of xasprintf-based code above:
+	* real 7.074s
+	* user 0.156s <<<
+	* sys 6.394s
+	* "rm -rf" of a Linux kernel tree from tmpfs (run time still dominated by in-kernel work, though)
+	* real 6.989s
+	* user 0.055s <<< 3 times less CPU used
+	* sys 6.450s
+	* vvvvvvvvvvv timing of open-coded malloc+memcpy code below (+59 bytes):
+	*/
+	char buf, p;
+	size_t n1, n2, n3;
+
+	while (*filename == '/')
+	filename++;
+
+	if (!path \|\| !path[0])
+	return xstrdup(filename);
+
+	n1 = strlen(path);
+	n2 = (path[n1 - 1] != '/'); /* 1: "path has no trailing slash" */
+	n3 = strlen(filename) + 1;
+
+	buf = xmalloc(n1 + n2 + n3);
+	p = mempcpy(buf, path, n1);
+	if (n2)
+	*p++ = '/';
+	p = mempcpy(p, filename, n3);
+	return buf;
+	#endif
+	}
+
+	/* If second component comes from struct dirent,
+	* it's possible to eliminate one strlen() by using name length
+	* provided by kernel in struct dirent. See below.
+	* However, the win seems to be insignificant.
+	*/
+
+	#if 0
+
+	/* Extract d_namlen from struct dirent */
+	static size_t get_d_namlen(const struct dirent *de)
+	{
+	#if defined(_DIRENT_HAVE_D_NAMLEN)
+	return de->d_namlen;
+	#elif defined(_DIRENT_HAVE_D_RECLEN)
+	const size_t prefix_sz = offsetof(struct dirent, d_name);
+	return de->d_reclen - prefix_sz;
+	#else
+	return strlen(de->d_name);
+	#endif
+	}
+
+	char* FAST_FUNC concat_path_dirent(const char path, const struct dirent de)
+	{
+	char buf, p;
+	size_t n1, n2, n3;
+
+	if (!path \|\| !path[0])
+	return xstrdup(de->d_name);
+
+	n1 = strlen(path);
+	n2 = (path[n1 - 1] != '/');
+	n3 = get_d_namlen(de) + 1;
+
+	buf = xmalloc(n1 + n2 + n3);
+	p = mempcpy(buf, path, n1);
+	if (n2)
+	*p++ = '/';
+	p = mempcpy(p, de->d_name, n3);
+	return buf;
	}
+
+	#endif

util-linux/lspci.c+1 -1

@@ -47,7 +47,7 @@ static int FAST_FUNC fileAction(struct recursive_state *state UNUSED_PARAM,
	int pci_class = 0, pci_vid = 0, pci_did = 0;
	int pci_subsys_vid = 0, pci_subsys_did = 0;

-	char *uevent_filename = concat_path_file(fileName, "/uevent");
+	char *uevent_filename = concat_path_file(fileName, "uevent");
	parser = config_open2(uevent_filename, fopen_for_read);
	free(uevent_filename);

util-linux/lsusb.c+1 -1

@@ -50,7 +50,7 @@ static int FAST_FUNC fileAction(struct recursive_state *state UNUSED_PARAM,
	char *tokens[4];
	char busnum = NULL, devnum = NULL;
	int product_vid = 0, product_did = 0;
-	char *uevent_filename = concat_path_file(fileName, "/uevent");
+	char *uevent_filename = concat_path_file(fileName, "uevent");

	parser = config_open2(uevent_filename, fopen_for_read);
	free(uevent_filename);