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	switch_root.c - ubase - suckless linux base utils
	git clone git://git.suckless.org/ubase
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	switch_root.c (2867B)
	---
	1 /* See LICENSE file for copyright and license details. */
	2 #include <sys/mount.h>
	3 #include <sys/stat.h>
	4 #include <sys/vfs.h>
	5
	6 #include <dirent.h>
	7 #include <fcntl.h>
	8 #include <limits.h>
	9 #include <stdio.h>
	10 #include <stdlib.h>
	11 #include <string.h>
	12 #include <unistd.h>
	13
	14 #include "util.h"
	15
	16 #define RAMFS_MAGIC 0x858458f6 /* some random numb…
	17 #define TMPFS_MAGIC 0x01021994
	18
	19 static void
	20 delete_content(const char *dir, dev_t curdevice)
	21 {
	22 char path[PATH_MAX];
	23 DIR *d;
	24 struct stat st;
	25 struct dirent *dent;
	26
	27 /* don't dive into other filesystems */
	28 if (lstat(dir, &st) < 0 \|\| st.st_dev != curdevice)
	29 return;
	30 if (!(d = opendir(dir)))
	31 return;
	32 while ((dent = readdir(d))) {
	33 if (strcmp(dent->d_name, ".") == 0 \|\|
	34 strcmp(dent->d_name, "..") == 0)
	35 continue;
	36
	37 /* build path and dive deeper */
	38 if (strlcpy(path, dir, sizeof(path)) >= sizeof(path))
	39 eprintf("path too long\n");
	40 if (path[strlen(path) - 1] != '/')
	41 if (strlcat(path, "/", sizeof(path)) >= sizeof(p…
	42 eprintf("path too long\n");
	43 if (strlcat(path, dent->d_name, sizeof(path)) >= sizeof(…
	44 eprintf("path too long\n");
	45
	46 if (lstat(path, &st) < 0)
	47 weprintf("lstat %s:", path);
	48
	49 if (S_ISDIR(st.st_mode)) {
	50 delete_content(path, curdevice);
	51 if (rmdir(path) < 0)
	52 weprintf("rmdir %s:", path);
	53 } else {
	54 if (unlink(path) < 0)
	55 weprintf("unlink %s:", path);
	56 }
	57 }
	58 closedir(d);
	59 }
	60
	61 static void
	62 usage(void)
	63 {
	64 eprintf("usage: %s [-c console] [newroot] [init] (PID 1)\n", arg…
	65 }
	66
	67 int
	68 main(int argc, char *argv[])
	69 {
	70 char *console = NULL;
	71 dev_t curdev;
	72 struct stat st;
	73 struct statfs stfs;
	74
	75 ARGBEGIN {
	76 case 'c':
	77 console = EARGF(usage());
	78 break;
	79 default:
	80 usage();
	81 } ARGEND;
	82
	83 /* check number of args and if we are PID 1 */
	84 if (argc != 2 \|\| getpid() != 1)
	85 usage();
	86
	87 /* chdir to newroot and make sure it's a different fs */
	88 if (chdir(argv[0]))
	89 eprintf("chdir %s:", argv[0]);
	90
	91 if (stat("/", &st))
	92 eprintf("stat %s:", "/");
	93
	94 curdev = st.st_dev;
	95 if (stat(".", &st))
	96 eprintf("stat %s:", ".");
	97 if (st.st_dev == curdev)
	98 usage();
	99
	100 /* avoids trouble with real filesystems */
	101 if (stat("/init", &st) \|\| !S_ISREG(st.st_mode))
	102 eprintf("/init is not a regular file\n");
	103
	104 statfs("/", &stfs);
	105 if ((unsigned)stfs.f_type != RAMFS_MAGIC && (unsigned)stfs.f_typ…
	106 eprintf("current filesystem is not a RAMFS or TMPFS\n");
	107
	108 /* wipe / */
	109 delete_content("/", curdev);
	110
	111 /* overmount / with newroot and chroot into it */
	112 if (mount(".", "/", NULL, MS_MOVE, NULL))
	113 eprintf("mount %s:", ".");
	114
	115 if (chroot("."))
	116 eprintf("chroot failed\n");
	117
	118 /* if -c is set, redirect stdin/stdout/stderr to console */
	119 if (console) {
	120 close(0);
	121 if (open(console, O_RDWR) == -1)
	122 eprintf("open %s:", console);
	123 dup2(0, 1);
	124 dup2(0, 2);
	125 }
	126
	127 /* execute init */
	128 execv(argv[1], argv);
	129 eprintf("can't execute '%s':", argv[1]);
	130 return 1;
	131 }