1#include <stdlib.h>
2#include <limits.h>
3#include <sys/stat.h>
4#include <fcntl.h>
5#include <errno.h>
6#include <unistd.h>
7#include <string.h>
8#include "syscall.h"
9
10void __procfdname(char *, unsigned);
11
12char *realpath(const char *restrict filename, char *restrict resolved)
13{
14	int fd;
15	ssize_t r;
16	struct stat st1, st2;
17	char buf[15+3*sizeof(int)];
18	char tmp[PATH_MAX];
19
20	if (!filename) {
21		errno = EINVAL;
22		return 0;
23	}
24
25	fd = sys_open(filename, O_PATH|O_NONBLOCK|O_CLOEXEC);
26	if (fd < 0) return 0;
27	__procfdname(buf, fd);
28
29	r = readlink(buf, tmp, sizeof tmp - 1);
30	if (r < 0) goto err;
31	tmp[r] = 0;
32
33	fstat(fd, &st1);
34	r = stat(tmp, &st2);
35	if (r<0 || st1.st_dev != st2.st_dev || st1.st_ino != st2.st_ino) {
36		if (!r) errno = ELOOP;
37		goto err;
38	}
39
40	__syscall(SYS_close, fd);
41	return resolved ? strcpy(resolved, tmp) : strdup(tmp);
42err:
43	__syscall(SYS_close, fd);
44	return 0;
45}
46