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process-util: add helper pidfd_get_pid()

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It returns the pid_t a pidfd refers to.
This commit is contained in:
Lennart Poettering 2019-10-30 16:35:48 +01:00
parent 5ead4e85f6
commit 298f466f15
2 changed files with 35 additions and 0 deletions
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33
src/basic/process-util.c
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@ -40,6 +40,7 @@
#include "rlimit-util.h"
#include "signal-util.h"
#include "stat-util.h"
#include "stdio-util.h"
#include "string-table.h"
#include "string-util.h"
#include "terminal-util.h"
@ -1488,6 +1489,38 @@ int set_oom_score_adjust(int value) {
WRITE_STRING_FILE_VERIFY_ON_FAILURE|WRITE_STRING_FILE_DISABLE_BUFFER);
}
int pidfd_get_pid(int fd, pid_t *ret) {
char path[STRLEN("/proc/self/fdinfo/") + DECIMAL_STR_MAX(int)];
_cleanup_free_ char *fdinfo = NULL;
char *p;
int r;
if (fd < 0)
return -EBADF;
xsprintf(path, "/proc/self/fdinfo/%i", fd);
r = read_full_file(path, &fdinfo, NULL);
if (r == -ENOENT) /* if fdinfo doesn't exist we assume the process does not exist */
return -ESRCH;
if (r < 0)
return r;
p = startswith(fdinfo, "Pid:");
if (!p) {
p = strstr(fdinfo, "\nPid:");
if (!p)
return -ENOTTY; /* not a pidfd? */
p += 5;
}
p += strspn(p, WHITESPACE);
p[strcspn(p, WHITESPACE)] = 0;
return parse_pid(p, ret);
}
static const char *const ioprio_class_table[] = {
[IOPRIO_CLASS_NONE] = "none",
[IOPRIO_CLASS_RT] = "realtime",

2
src/basic/process-util.h
View File

@ -197,3 +197,5 @@ assert_cc(TASKS_MAX <= (unsigned long) PID_T_MAX);
(pid) = 0; \
_pid_; \
})
int pidfd_get_pid(int fd, pid_t *ret);