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mount-util: make sure mount_switch_root() works as clean NOP when '/' is specified as target

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This commit is contained in:
Lennart Poettering
2023-12-14 13:13:45 +09:00
committed by Yu Watanabe
parent 1fdab6c306
commit bb59b92256
2 changed files with 43 additions and 27 deletions
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src/shared/mount-util.c
+25 -21
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@@ -457,10 +457,6 @@ static int mount_switch_root_pivot(int fd_newroot, const char *path) {
assert(fd_newroot >= 0);
assert(path);
/* Change into the new rootfs. */
if (fchdir(fd_newroot) < 0)
return log_debug_errno(errno, "Failed to chdir into new rootfs '%s': %m", path);
/* Let the kernel tuck the new root under the old one. */
if (pivot_root(".", ".") < 0)
return log_debug_errno(errno, "Failed to pivot root to new rootfs '%s': %m", path);
@@ -477,10 +473,6 @@ static int mount_switch_root_move(int fd_newroot, const char *path) {
assert(fd_newroot >= 0);
assert(path);
/* Change into the new rootfs. */
if (fchdir(fd_newroot) < 0)
return log_debug_errno(errno, "Failed to chdir into new rootfs '%s': %m", path);
/* Move the new root fs */
if (mount(".", "/", NULL, MS_MOVE, NULL) < 0)
return log_debug_errno(errno, "Failed to move new rootfs '%s': %m", path);
@@ -494,7 +486,7 @@ static int mount_switch_root_move(int fd_newroot, const char *path) {
int mount_switch_root_full(const char *path, unsigned long mount_propagation_flag, bool force_ms_move) {
_cleanup_close_ int fd_newroot = -EBADF;
int r;
int r, is_current_root;
assert(path);
assert(mount_propagation_flag_is_valid(mount_propagation_flag));
@@ -503,19 +495,31 @@ int mount_switch_root_full(const char *path, unsigned long mount_propagation_fla
if (fd_newroot < 0)
return log_debug_errno(errno, "Failed to open new rootfs '%s': %m", path);
if (!force_ms_move) {
r = mount_switch_root_pivot(fd_newroot, path);
if (r < 0) {
log_debug_errno(r, "Failed to pivot into new rootfs '%s', will try to use MS_MOVE instead: %m", path);
force_ms_move = true;
is_current_root = path_is_root_at(fd_newroot, NULL);
if (is_current_root < 0)
return log_debug_errno(is_current_root, "Failed to determine if target dir is our root already: %m");
/* Change into the new rootfs. */
if (fchdir(fd_newroot) < 0)
return log_debug_errno(errno, "Failed to chdir into new rootfs '%s': %m", path);
/* Make this a NOP if we are supposed to switch to our current root fs. After all, both pivot_root()
* and MS_MOVE don't like that. */
if (!is_current_root) {
if (!force_ms_move) {
r = mount_switch_root_pivot(fd_newroot, path);
if (r < 0) {
log_debug_errno(r, "Failed to pivot into new rootfs '%s', will try to use MS_MOVE instead: %m", path);
force_ms_move = true;
}
}
if (force_ms_move) {
/* Failed to pivot_root() fallback to MS_MOVE. For example, this may happen if the rootfs is
* an initramfs in which case pivot_root() isn't supported. */
r = mount_switch_root_move(fd_newroot, path);
if (r < 0)
return log_debug_errno(r, "Failed to switch to new rootfs '%s' with MS_MOVE: %m", path);
}
}
if (force_ms_move) {
/* Failed to pivot_root() fallback to MS_MOVE. For example, this may happen if the rootfs is
* an initramfs in which case pivot_root() isn't supported. */
r = mount_switch_root_move(fd_newroot, path);
if (r < 0)
return log_debug_errno(r, "Failed to switch to new rootfs '%s' with MS_MOVE: %m", path);
}
/* Finally, let's establish the requested propagation flags. */