This reverts commit a692a8745941a192528c5e2a05de97155ba586f9.
Booting into a system this way just leads to problems because
you cannot remount the root read-only at shutdown (leading to unclean
shutdowns).
Miklos Szeredi pointed out a trick to turn any directory into a
mount point which avoids this problem. Therefore we can simplify
switch_root again and simply document that its users should set
up the root as a mount point beforehand.
---
sys-utils/switch_root.8 | 13 +++++++
sys-utils/switch_root.c | 81 +++--------------------------------------------
2 files changed, 18 insertions(+), 76 deletions(-)
diff --git a/sys-utils/switch_root.8 b/sys-utils/switch_root.8
index 4fdc8e9..b6712ec 100644
--- a/sys-utils/switch_root.8
+++ b/sys-utils/switch_root.8
@@ -32,6 +32,19 @@ show version number and exit
.B switch_root
returns 0 on success and 1 on failure.
+.SH NOTES
+switch_root will fail to function if
+.B newroot
+is not the root of a mount. If you want to switch root into a directory that
+does not meet this requirement then you can first use a bind-mounting trick to
+turn any directory into a mount point:
+.sp
+.nf
+.RS
+mount --bind $DIR $DIR
+.RE
+.fi
+
.SH "SEE ALSO"
.BR mount (8)
.BR chroot (2)
diff --git a/sys-utils/switch_root.c b/sys-utils/switch_root.c
index 174e667..c43225d 100644
--- a/sys-utils/switch_root.c
+++ b/sys-utils/switch_root.c
@@ -33,7 +33,6 @@
#include <ctype.h>
#include <dirent.h>
#include <err.h>
-#include <libgen.h>
#ifndef MS_MOVE
#define MS_MOVE 8192
@@ -109,58 +108,13 @@ done:
return rc;
}
-/* find the enclosing mount point of a path, by examining the backing device
- * of parent directories until we reach / or find a parent with a differing
- * device. Result must be freed.
- */
-static char *get_parent_mount(const char *path)
-{
- struct stat sb;
- char *dir;
- char tmp[PATH_MAX];
- dev_t inner_dev;
-
- if (stat(path, &sb) != 0) {
- warn("failed to stat %s", path);
- return NULL;
- }
-
- inner_dev = sb.st_dev;
- dir = strdup(path);
-
- while (dir) {
- char *parent;
-
- strncpy(tmp, dir, PATH_MAX);
- tmp[PATH_MAX - 1] = '\0';
- parent = dirname(tmp);
-
- if (stat(parent, &sb) != 0) {
- warn("failed to stat %s", parent);
- return NULL;
- }
- if (sb.st_dev != inner_dev)
- return dir;
-
- strncpy(dir, parent, PATH_MAX);
- dir[PATH_MAX - 1] = '\0';
-
- /* maybe we've reached / */
- if (*dir == '/' && !*(dir + 1))
- return dir;
- }
- return NULL;
-}
-
static int switchroot(const char *newroot)
{
/* Don't try to unmount the old "/", there's no way to do it. */
const char *umounts[] = { "/dev", "/proc", "/sys", NULL };
int i;
- int cfd, rc = -1;
+ int cfd;
pid_t pid;
- const char *chroot_path = NULL;
- char *newroot_mnt;
for (i = 0; umounts[i] != NULL; i++) {
char newmount[PATH_MAX];
@@ -175,43 +129,21 @@ static int switchroot(const char *newroot)
}
}
- newroot_mnt = get_parent_mount(newroot);
- if (newroot_mnt && strcmp(newroot, newroot_mnt)) {
- /* newroot is not a mount point, so we have to MS_MOVE the
- * parent mount point and then chroot in to the "subroot"
- */
- chroot_path = newroot + strlen(newroot_mnt);
- newroot = newroot_mnt;
- }
-
if (chdir(newroot)) {
warn("failed to change directory to %s", newroot);
- goto done;
+ return -1;
}
cfd = open("/", O_RDONLY);
if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
warn("failed to mount moving %s to /", newroot);
- goto done;
+ return -1;
}
- /* move to the real root of the device */
if (chroot(".")) {
warn("failed to change root");
- goto done;
- }
-
- /* move to the subdirectory on the root device (subroot) */
- if (chroot_path) {
- if (chdir(chroot_path)) {
- warn("failed to chdir to subroot %s", chroot_path);
- goto done;
- }
- if (chroot(".")) {
- warn("failed to change root to subroot %s", chroot_path);
- goto done;
- }
+ return -1;
}
if (cfd >= 0) {
@@ -223,10 +155,7 @@ static int switchroot(const char *newroot)
}
close(cfd);
}
- rc = 0;
-done:
- free(newroot_mnt);
- return rc;
+ return 0;
}
static void usage(FILE *output)
--
1.6.2.5
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