Commit ab7d9b67 authored by Holger Hans Peter Freyther's avatar Holger Hans Peter Freyther Committed by Lennart Poettering
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util: Avoid memory allocations for formatting paths

Avoid memory allocations to construct the path for files in the
procfs. The procfs paths are way shorter than the PATH_MAX so we
can use snprintf on a string located on the stack. This shows up
as a win on x86 using the benchmark program below.

$ make libsystemd-shared.la; gcc -O2 -Isrc/systemd/ -Isrc/ \
	-o simple-perf-test simple-perf-test.c \
	.libs/libsystemd-shared.a  -lrt

 #include "shared/util.h"
void test_once(void) {
	pid_t pid = getpid();
	char *tmp = NULL;

	get_process_comm(pid, &tmp);
	free(tmp);
	tmp = NULL;
	get_process_cmdline(pid, 0, 1, &tmp);
	free(tmp);
	is_kernel_thread(pid);
	tmp = NULL;
	get_process_exe(pid, &tmp);
	free(tmp);
}

int main(int argc, char **argv)
{
	int i;
	for (i = 0; i < 50000; ++i)
		test_once();
}
parent b6b7d433
......@@ -80,6 +80,16 @@ char **saved_argv = NULL;
static volatile unsigned cached_columns = 0;
static volatile unsigned cached_lines = 0;
#define PROCFS_PATH_LEN (sizeof("/proc/")-1 + DECIMAL_STR_MAX(pid_t))
#define FORMAT_PROCFS_PATH(buffer, path, pid) \
do { \
assert_cc(sizeof(buffer) == (PROCFS_PATH_LEN + 1 + sizeof(path))); \
snprintf(buffer, sizeof(buffer) - 1, "/proc/%lu/%s", (unsigned long) pid, path); \
char_array_0(buffer); \
} while(0)
size_t page_size(void) {
static __thread size_t pgsz = 0;
long r;
......@@ -571,12 +581,9 @@ int get_process_comm(pid_t pid, char **name) {
if (pid == 0)
r = read_one_line_file("/proc/self/comm", name);
else {
char *p;
if (asprintf(&p, "/proc/%lu/comm", (unsigned long) pid) < 0)
return -ENOMEM;
r = read_one_line_file(p, name);
free(p);
char path[PROCFS_PATH_LEN + sizeof("/comm")];
FORMAT_PROCFS_PATH(path, "comm", pid);
r = read_one_line_file(path, name);
}
return r;
......@@ -592,12 +599,9 @@ int get_process_cmdline(pid_t pid, size_t max_length, bool comm_fallback, char *
if (pid == 0)
f = fopen("/proc/self/cmdline", "re");
else {
char *p;
if (asprintf(&p, "/proc/%lu/cmdline", (unsigned long) pid) < 0)
return -ENOMEM;
f = fopen(p, "re");
free(p);
char path[PROCFS_PATH_LEN + sizeof("/cmdline")];
FORMAT_PROCFS_PATH(path, "cmdline", pid);
f = fopen(path, "re");
}
if (!f)
......@@ -684,7 +688,7 @@ int get_process_cmdline(pid_t pid, size_t max_length, bool comm_fallback, char *
}
int is_kernel_thread(pid_t pid) {
char *p;
char path[PROCFS_PATH_LEN + sizeof("/cmdline")];
size_t count;
char c;
bool eof;
......@@ -693,11 +697,8 @@ int is_kernel_thread(pid_t pid) {
if (pid == 0)
return 0;
if (asprintf(&p, "/proc/%lu/cmdline", (unsigned long) pid) < 0)
return -ENOMEM;
f = fopen(p, "re");
free(p);
FORMAT_PROCFS_PATH(path, "cmdline", pid);
f = fopen(path, "re");
if (!f)
return -errno;
......@@ -722,12 +723,9 @@ int get_process_exe(pid_t pid, char **name) {
if (pid == 0)
r = readlink_malloc("/proc/self/exe", name);
else {
char *p;
if (asprintf(&p, "/proc/%lu/exe", (unsigned long) pid) < 0)
return -ENOMEM;
r = readlink_malloc(p, name);
free(p);
char path[PROCFS_PATH_LEN + sizeof("/exe")];
FORMAT_PROCFS_PATH(path, "exe", pid);
r = readlink_malloc(path, name);
}
return r;
......@@ -735,7 +733,7 @@ int get_process_exe(pid_t pid, char **name) {
static int get_process_id(pid_t pid, const char *field, uid_t *uid) {
_cleanup_fclose_ FILE *f = NULL;
_cleanup_free_ char *p = NULL;
char path[PROCFS_PATH_LEN + sizeof("/status")];
char line[LINE_MAX];
assert(field);
......@@ -744,10 +742,8 @@ static int get_process_id(pid_t pid, const char *field, uid_t *uid) {
if (pid == 0)
return getuid();
if (asprintf(&p, "/proc/%lu/status", (unsigned long) pid) < 0)
return -ENOMEM;
f = fopen(p, "re");
FORMAT_PROCFS_PATH(path, "status", pid);
f = fopen(path, "re");
if (!f)
return -errno;
......
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