mdmon: --switch-root

For raid rootfs we cannot run the array unmonitored for any length of
time.  At least XFS will not mount/replay the journal if the underlying
block device is readonly (FIXME it also seems that XFS does not always
honor the ro status of the backing device as I was able to hit the
BUG_ON(mddev->ro == 1) in md_write_start... but I digress).

So we need to start mdmon in the initramfs before '/' is mounted and
then restart it after the real rootfs is available.  Upon seeing the
--switch-root option, mdmon will kill any victims in the current
/var/run/mdadm directory and then chroot(2) before continuing.

The option is deliberately called 'switch-root' instead of 'chroot' to
hopefully indicate that this is different than doing "chroot mdmon
/dev/imsm".

Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/mdmon.c b/mdmon.c
index d40adb26706ae732075f591eacd540fc1c99bc3c..877cf1a16762315b6378fa62061cb155f4aed3bb 100644 (file)
--- a/mdmon.c
+++ b/mdmon.c
@@ -38,6 +38,7 @@
 #include       <string.h>
 #include       <fcntl.h>
 #include       <signal.h>
 #include       <string.h>
 #include       <fcntl.h>
 #include       <signal.h>

+#include       <dirent.h>

 
 #include       <sched.h>
 
 
 #include       <sched.h>
 


@@ -233,7 +234,11 @@ static int do_fork(void)
        return 1;
 }
 
        return 1;
 }
 

-
+void usage(void)
+{
+       fprintf(stderr, "Usage: mdmon [--switch-root dir] /device/name/for/container\n");
+       exit(2);
+}

 
 int main(int argc, char *argv[])
 {
 
 int main(int argc, char *argv[])
 {


@@ -245,20 +250,34 @@ int main(int argc, char *argv[])
        int pfd[2];
        int status;
        int ignore;
        int pfd[2];
        int status;
        int ignore;

-
-       if (argc != 2) {
-               fprintf(stderr, "Usage: md-manage /device/name/for/container\n");
-               exit(2);
+       char *container_name = NULL;
+       char *switchroot = NULL;
+
+       switch (argc) {
+       case 2:
+               container_name = argv[1];
+               break;
+       case 4:
+               if (strcmp(argv[1], "--switch-root") != 0) {
+                       fprintf(stderr, "mdmon: unknown argument %s\n", argv[1]);
+                       usage();
+               }
+               switchroot = argv[2];
+               container_name = argv[3];
+               break;
+       default:
+               usage();

        }
        }

-       mdfd = open(argv[1], O_RDWR);
+
+       mdfd = open(container_name, O_RDWR);

        if (mdfd < 0) {
        if (mdfd < 0) {

-               fprintf(stderr, "md-manage: %s: %s\n", argv[1],
+               fprintf(stderr, "mdmon: %s: %s\n", container_name,

                        strerror(errno));
                exit(1);
        }
        if (md_get_version(mdfd) < 0) {
                        strerror(errno));
                exit(1);
        }
        if (md_get_version(mdfd) < 0) {

-               fprintf(stderr, "md-manage: %s: Not an md device\n",
-                       argv[1]);
+               fprintf(stderr, "mdmon: %s: Not an md device\n",
+                       container_name);

                exit(1);
        }
 
                exit(1);
        }
 


@@ -286,12 +305,53 @@ int main(int argc, char *argv[])
                }
        } else
                pfd[0] = pfd[1] = -1;
                }
        } else
                pfd[0] = pfd[1] = -1;

-       /* hopefully it is a container - we'll check later */

 
        container = malloc(sizeof(*container));
        container->devnum = fd2devnum(mdfd);
        container->devname = devnum2devname(container->devnum);
 
        container = malloc(sizeof(*container));
        container->devnum = fd2devnum(mdfd);
        container->devname = devnum2devname(container->devnum);

-       container->device_name = argv[1];
+       container->device_name = container_name;
+       container->arrays = NULL;
+
+       if (!container->devname) {
+               fprintf(stderr, "mdmon: failed to allocate container name string\n");
+               exit(3);
+       }
+
+       mdi = sysfs_read(mdfd, container->devnum,
+                        GET_VERSION|GET_LEVEL|GET_DEVS);
+
+       if (!mdi) {
+               fprintf(stderr, "mdmon: failed to load sysfs info for %s\n",
+                       container->devname);
+               exit(3);
+       }
+       if (mdi->array.level != UnSet) {
+               fprintf(stderr, "mdmon: %s is not a container - cannot monitor\n",
+                       container_name);
+               exit(3);
+       }
+       if (mdi->array.major_version != -1 ||
+           mdi->array.minor_version != -2) {
+               fprintf(stderr, "mdmon: %s does not use external metadata - cannot monitor\n",
+                       container_name);
+               exit(3);
+       }
+
+       container->ss = find_metadata_methods(mdi->text_version);
+       if (container->ss == NULL) {
+               fprintf(stderr, "mdmon: %s uses unknown metadata: %s\n",
+                       container_name, mdi->text_version);
+               exit(3);
+       }
+
+       container->devs = NULL;
+       for (di = mdi->devs; di; di = di->next) {
+               struct mdinfo *cd = malloc(sizeof(*cd));
+               *cd = *di;
+               cd->next = container->devs;
+               container->devs = cd;
+       }
+       sysfs_free(mdi);

 
        /* SIGUSR is sent between parent and child.  So both block it
         * and enable it only with pselect.
 
        /* SIGUSR is sent between parent and child.  So both block it
         * and enable it only with pselect.


@@ -313,9 +373,28 @@ int main(int argc, char *argv[])
        act.sa_handler = SIG_IGN;
        sigaction(SIGPIPE, &act, NULL);
 
        act.sa_handler = SIG_IGN;
        sigaction(SIGPIPE, &act, NULL);
 

-       /* If this fails, we hope it already exists */
+       if (switchroot) {
+               /* we assume we assume that /sys /proc /dev are available in
+                * the new root (see nash:setuproot)
+                *
+                * kill any monitors in the current namespace and change
+                * to the new one
+                */
+               try_kill_monitor(container->devname);
+               if (chroot(switchroot) != 0) {
+                       fprintf(stderr, "mdmon: failed to chroot to '%s': %s\n",
+                               switchroot, strerror(errno));
+                       exit(4);
+               }
+       }
+
+       /* If this fails, we hope it already exists 
+        * pid file lives in /var/run/mdadm/mdXX.pid
+        */
+       mkdir("/var", 0600);
+       mkdir("/var/run", 0600);

        mkdir("/var/run/mdadm", 0600);
        mkdir("/var/run/mdadm", 0600);

-       /* pid file lives in /var/run/mdadm/mdXX.pid */
+       ignore = chdir("/");

        if (make_pidfile(container->devname, O_EXCL) < 0) {
                if (ping_monitor(container->devname) == 0) {
                        fprintf(stderr, "mdmon: %s already managed\n",
        if (make_pidfile(container->devname, O_EXCL) < 0) {
                if (ping_monitor(container->devname) == 0) {
                        fprintf(stderr, "mdmon: %s already managed\n",


@@ -341,50 +420,11 @@ int main(int argc, char *argv[])
                        }
                }
        }
                        }
                }
        }

-

        container->sock = make_control_sock(container->devname);
        container->sock = make_control_sock(container->devname);

-       container->arrays = NULL;
-
-       mdi = sysfs_read(mdfd, container->devnum,
-                        GET_VERSION|GET_LEVEL|GET_DEVS);

 
 

-       if (!mdi) {
-               fprintf(stderr, "mdmon: failed to load sysfs info for %s\n",
-                       container->devname);
-               exit(3);
-       }
-       if (mdi->array.level != UnSet) {
-               fprintf(stderr, "mdmon: %s is not a container - cannot monitor\n",
-                       argv[1]);
-               exit(3);
-       }
-       if (mdi->array.major_version != -1 ||
-           mdi->array.minor_version != -2) {
-               fprintf(stderr, "mdmon: %s does not use external metadata - cannot monitor\n",
-                       argv[1]);
-               exit(3);
-       }
-
-       container->ss = find_metadata_methods(mdi->text_version);
-       if (container->ss == NULL) {
-               fprintf(stderr, "mdmon: %s uses unknown metadata: %s\n",
-                       argv[1], mdi->text_version);
-               exit(3);
-       }
-
-       container->devs = NULL;
-       for (di = mdi->devs; di; di = di->next) {
-               struct mdinfo *cd = malloc(sizeof(*cd));
-               *cd = *di;
-               cd->next = container->devs;
-               container->devs = cd;
-       }
-       sysfs_free(mdi);
-
-
-       if (container->ss->load_super(container, mdfd, argv[1])) {
+       if (container->ss->load_super(container, mdfd, container_name)) {

                fprintf(stderr, "mdmon: Cannot load metadata for %s\n",
                fprintf(stderr, "mdmon: Cannot load metadata for %s\n",

-                       argv[1]);
+                       container_name);

                exit(3);
        }
 
                exit(3);
        }
 


@@ -396,7 +436,6 @@ int main(int argc, char *argv[])
                        getppid());
        close(pfd[1]);
 
                        getppid());
        close(pfd[1]);
 

-       ignore = chdir("/");

        setsid();
        close(0);
        open("/dev/null", O_RDWR);
        setsid();
        close(0);
        open("/dev/null", O_RDWR);