run-init: implement -n "dry run"

function                                             old     new   delta
switch_root_main                                     637     706     +69
packed_usage                                       31743   31757     +14
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 83/0)               Total: 83 bytes
   text	   data	    bss	    dec	    hex	filename
 915247	    563	   5844	 921654	  e1036	busybox_old
 915303	    563	   5844	 921710	  e106e	busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/selinux/setfiles.c b/selinux/setfiles.c
index fca698296251cd15443e72a4024768968e195f38..8da47d274a377aae7d0b9cf987a7bc2d2e137aba 100644 (file)
--- a/selinux/setfiles.c
+++ b/selinux/setfiles.c
@@ -679,7 +679,7 @@ int setfiles_main(int argc UNUSED_PARAM, char **argv)
                        bb_show_usage();
                xstat(argv[0], &sb);
                if (!S_ISREG(sb.st_mode)) {
-                       bb_error_msg_and_die("spec file %s is not a regular file", argv[0]);
+                       bb_error_msg_and_die("'%s' is not a regular file", argv[0]);
                }
                /* Load the file contexts configuration and check it. */
                rc = matchpathcon_init(argv[0]);

diff --git a/util-linux/switch_root.c b/util-linux/switch_root.c
index fe9ab68d0d5e76b8231012c94dea1e546a0104f5..16abcb634fe60d92670a3961acde603a7ebd036e 100644 (file)
--- a/util-linux/switch_root.c
+++ b/util-linux/switch_root.c
@@ -24,6 +24,8 @@
 //config:      * Because the Linux kernel uses rootfs internally as the starting
 //config:      and ending point for searching through the kernel's doubly linked
 //config:      list of active mount points. That's why.
+//config:
+// RUN_INIT config item is in klibc-utils
 
 //applet:IF_SWITCH_ROOT(APPLET(switch_root, BB_DIR_SBIN, BB_SUID_DROP))
 //                      APPLET_ODDNAME:name      main         location     suid_type     help
@@ -32,23 +34,6 @@
 //kbuild:lib-$(CONFIG_SWITCH_ROOT) += switch_root.o
 //kbuild:lib-$(CONFIG_RUN_INIT)    += switch_root.o
 
-//usage:#define switch_root_trivial_usage
-//usage:       "[-c CONSOLE_DEV] NEW_ROOT NEW_INIT [ARGS]"
-//usage:#define switch_root_full_usage "\n\n"
-//usage:       "Free initramfs and switch to another root fs:\n"
-//usage:       "chroot to NEW_ROOT, delete all in /, move NEW_ROOT to /,\n"
-//usage:       "execute NEW_INIT. PID must be 1. NEW_ROOT must be a mountpoint.\n"
-//usage:     "\n       -c DEV  Reopen stdio to DEV after switch"
-
-//usage:#define run_init_trivial_usage
-//usage:       "[-d CAP,CAP...] [-c CONSOLE_DEV] NEW_ROOT NEW_INIT [ARGS]"
-//usage:#define run_init_full_usage "\n\n"
-//usage:       "Free initramfs and switch to another root fs:\n"
-//usage:       "chroot to NEW_ROOT, delete all in /, move NEW_ROOT to /,\n"
-//usage:       "execute NEW_INIT. PID must be 1. NEW_ROOT must be a mountpoint.\n"
-//usage:     "\n       -c DEV  Reopen stdio to DEV after switch"
-//usage:     "\n       -d CAPS Drop capabilities"
-
 #include <sys/vfs.h>
 #include <sys/mount.h>
 #if ENABLE_RUN_INIT
@@ -122,13 +107,8 @@ static void drop_capset(int cap_idx)
 {
        struct caps caps;
 
-       /* Get the current capability mask */
        getcaps(&caps);
-
-       /* Drop the bit */
        caps.data[CAP_TO_INDEX(cap_idx)].inheritable &= ~CAP_TO_MASK(cap_idx);
-
-       /* And drop the capability. */
        if (capset(&caps.header, caps.data) != 0)
                bb_perror_msg_and_die("capset");
 }
@@ -199,10 +179,18 @@ int switch_root_main(int argc UNUSED_PARAM, char **argv)
        char *newroot, *console = NULL;
        struct stat st;
        struct statfs stfs;
+       unsigned dry_run = 0;
        dev_t rootdev;
 
-       // Parse args (-c console). '+': stop at first non-option
+       // Parse args. '+': stop at first non-option
        if (ENABLE_SWITCH_ROOT && (!ENABLE_RUN_INIT || applet_name[0] == 's')) {
+//usage:#define switch_root_trivial_usage
+//usage:       "[-c CONSOLE_DEV] NEW_ROOT NEW_INIT [ARGS]"
+//usage:#define switch_root_full_usage "\n\n"
+//usage:       "Free initramfs and switch to another root fs:\n"
+//usage:       "chroot to NEW_ROOT, delete all in /, move NEW_ROOT to /,\n"
+//usage:       "execute NEW_INIT. PID must be 1. NEW_ROOT must be a mountpoint.\n"
+//usage:     "\n       -c DEV  Reopen stdio to DEV after switch"
                getopt32(argv, "^+"
                        "c:"
                        "\0" "-2" /* minimum 2 args */,
@@ -210,13 +198,23 @@ int switch_root_main(int argc UNUSED_PARAM, char **argv)
                );
        } else {
 #if ENABLE_RUN_INIT
+//usage:#define run_init_trivial_usage
+//usage:       "[-d CAP,CAP...] [-n] [-c CONSOLE_DEV] NEW_ROOT NEW_INIT [ARGS]"
+//usage:#define run_init_full_usage "\n\n"
+//usage:       "Free initramfs and switch to another root fs:\n"
+//usage:       "chroot to NEW_ROOT, delete all in /, move NEW_ROOT to /,\n"
+//usage:       "execute NEW_INIT. PID must be 1. NEW_ROOT must be a mountpoint.\n"
+//usage:     "\n       -c DEV  Reopen stdio to DEV after switch"
+//usage:     "\n       -d CAPS Drop capabilities"
+//usage:     "\n       -n      Dry run"
                char *cap_list = NULL;
-               getopt32(argv, "^+"
-                       "c:d:"
+               dry_run = getopt32(argv, "^+"
+                       "c:d:n"
                        "\0" "-2" /* minimum 2 args */,
                        &console,
                        &cap_list
                );
+               dry_run >>= 2; // -n
                if (cap_list)
                        drop_capabilities(cap_list);
 #endif
@@ -239,7 +237,7 @@ int switch_root_main(int argc UNUSED_PARAM, char **argv)
        // we mean it. I could make this a CONFIG option, but I would get email
        // from all the people who WILL destroy their filesystems.
        if (stat("/init", &st) != 0 || !S_ISREG(st.st_mode)) {
-               bb_error_msg_and_die("/init is not a regular file");
+               bb_error_msg_and_die("'%s' is not a regular file", "/init");
        }
        statfs("/", &stfs); // this never fails
        if ((unsigned)stfs.f_type != RAMFS_MAGIC
@@ -248,13 +246,15 @@ int switch_root_main(int argc UNUSED_PARAM, char **argv)
                bb_error_msg_and_die("root filesystem is not ramfs/tmpfs");
        }
 
-       // Zap everything out of rootdev
-       delete_contents("/", rootdev);
+       if (!dry_run) {
+               // Zap everything out of rootdev
+               delete_contents("/", rootdev);
 
-       // Overmount / with newdir and chroot into it
-       if (mount(".", "/", NULL, MS_MOVE, NULL)) {
-               // For example, fails when newroot is not a mountpoint
-               bb_perror_msg_and_die("error moving root");
+               // Overmount / with newdir and chroot into it
+               if (mount(".", "/", NULL, MS_MOVE, NULL)) {
+                       // For example, fails when newroot is not a mountpoint
+                       bb_perror_msg_and_die("error moving root");
+               }
        }
        xchroot(".");
        // The chdir is needed to recalculate "." and ".." links
@@ -270,8 +270,17 @@ int switch_root_main(int argc UNUSED_PARAM, char **argv)
                }
        }
 
-       // Exec real init
-       execv(argv[0], argv);
+       if (dry_run) {
+               // Does NEW_INIT look like it can be executed?
+               //xstat(argv[0], &st);
+               //if (!S_ISREG(st.st_mode))
+               //      bb_perror_msg_and_die("'%s' is not a regular file", argv[0]);
+               if (access(argv[0], X_OK) == 0)
+                       return 0;
+       } else {
+               // Exec NEW_INIT
+               execv(argv[0], argv);
+       }
        bb_perror_msg_and_die("can't execute '%s'", argv[0]);
 }