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();
}
static volatile unsigned cached_columns = 0;
static volatile unsigned cached_lines = 0;
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;
size_t page_size(void) {
static __thread size_t pgsz = 0;
long r;
if (pid == 0)
r = read_one_line_file("/proc/self/comm", name);
else {
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);
if (pid == 0)
f = fopen("/proc/self/cmdline", "re");
else {
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");
}
int is_kernel_thread(pid_t pid) {
}
int is_kernel_thread(pid_t pid) {
+ char path[PROCFS_PATH_LEN + sizeof("/cmdline")];
size_t count;
char c;
bool eof;
size_t count;
char c;
bool eof;
- 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 (pid == 0)
r = readlink_malloc("/proc/self/exe", name);
else {
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);
static int get_process_id(pid_t pid, const char *field, uid_t *uid) {
_cleanup_fclose_ FILE *f = NULL;
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);
char line[LINE_MAX];
assert(field);
if (pid == 0)
return getuid();
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");