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# T2 SDE: package/*/embutils/x-switch_root.patch
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pivot_root'ing rootfs does uncover kernel inf. loops, thus I extraced some
bits form the Fedora Core's nash to trick around with moving the mount point
and chroot to move the real root device to / - yuck.

   - Rene Rebe <rene@exactcode.de>

--- embutils-0.17/switch_root.c	1970-01-01 00:00:00.000000000 +0000
+++ embutils-0.17-more/switch_root.c	2005-08-27 09:05:22.000000000 +0000
@@ -0,0 +1,151 @@
+
+/* inspired by Fedora Core's mkinitrd/nash beast
+     - to pivot_root alike functionality with initramfs
+
+   2005 by Rene Rebe 
+ */
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <dirent.h>
+#include <stdio.h>
+#include <errno.h>
+
+#ifndef MS_REMOUNT
+#define MS_REMOUNT      32
+#endif
+
+#ifndef MS_BIND
+#define MS_BIND 4096
+#endif
+
+#ifndef MS_MOVE
+#define MS_MOVE 8192
+#endif
+
+/* remove all files/directories below dirName -- don't cross mountpoints */
+int recursiveRemove(char * dirName) {
+    struct stat sb,rb;
+    DIR * dir;
+    struct dirent * d;
+    char * strBuf = alloca(strlen(dirName) + 1024);
+
+    if (!(dir = opendir(dirName))) {
+	fprintf(stderr, "error opening %s: %d\n", dirName, errno);
+	return 0;
+    }
+
+    if (fstat(dirfd(dir),&rb)) {
+	fprintf(stderr, "unable to stat %s: %d\n", dirName, errno);
+	return 0;
+    }
+
+    errno = 0;
+    while ((d = readdir(dir))) {
+	errno = 0;
+
+	if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, "..")) {
+	    errno = 0;
+	    continue;
+	}
+
+	strcpy(strBuf, dirName);
+	strcat(strBuf, "/");
+	strcat(strBuf, d->d_name);
+
+	if (lstat(strBuf, &sb)) {
+	    fprintf(stderr, "failed to stat %s: %d\n", strBuf, errno);
+	    errno = 0;
+	    continue;
+	}
+
+	/* only descend into subdirectories if device is same as dir */
+	if (S_ISDIR(sb.st_mode)) {
+	    if (sb.st_dev == rb.st_dev) {
+	        recursiveRemove(strBuf);
+	        if (rmdir(strBuf))
+		    fprintf(stderr, "failed to rmdir %s: %d\n", strBuf, errno);
+	    }
+	    errno = 0;
+	    continue;
+	}
+
+	if (unlink(strBuf)) {
+	    fprintf(stderr, "failed to remove %s: %d\n", strBuf, errno);
+	    errno = 0;
+	    continue;
+	}
+    }
+
+    if (errno) {
+	closedir(dir);
+	printf("error reading from %s: %d\n", dirName, errno);
+	return 1;
+    }
+
+    closedir(dir);
+
+    return 0;
+}
+
+/* 2.6 magic not-pivot-root but kind of similar stuff.
+ * This is based on code from klibc/utils/run_init.c
+ */
+int main (int argc, char* argv[]) {
+    char * new;
+
+    if (!*++argv) {
+        printf("switch_root: new root mount point expected\n");
+        return 1;
+    }
+    new = *argv;
+
+    if (!*++argv) {
+        printf("switch_root: new init expected\n");
+	return 1;
+    }
+
+    int fd, i = 0;
+
+    if (chdir(new)) {
+        printf("switch_root: chdir(%s) failed: %d\n", new, errno);
+        return 1;
+    }
+
+    if ((fd = open("./dev/console", O_RDWR)) < 0) {
+        printf("ERROR opening /dev/console!!!!: %d\n", errno);
+        fd = 0;
+    }
+
+    if (dup2(fd, 0) != 0) printf("error dup2'ing fd of %d to 0\n", fd);
+    if (dup2(fd, 1) != 1) printf("error dup2'ing fd of %d to 1\n", fd);
+    if (dup2(fd, 2) != 2) printf("error dup2'ing fd of %d to 2\n", fd);
+    if (fd > 2)
+        close(fd);
+
+    recursiveRemove("/");
+
+    fd = open("/", O_RDONLY);
+
+    if (mount(".", "/", NULL, MS_MOVE, NULL)) {
+        printf("switch_root: mount failed: %d\n", errno);
+        close(fd);
+        return 1;
+    }
+
+    if (chroot(".") || chdir("/")) {
+        printf("switch_root: chroot() failed: %d\n", errno);
+        close(fd);
+        return 1;
+    }
+
+    /* release the old "/" */
+    close(fd);
+
+    /* exec the init */
+    fd = execvp (argv[0], argv);
+    printf ("switch_root: execvp failed: %d\n", fd);
+    return fd;
+}
+
--- ./Makefile~	2006-11-05 11:53:42.000000000 +0100
+++ ./Makefile	2006-11-05 11:53:57.000000000 +0100
@@ -13,7 +13,7 @@
 sosrm soscp sosmv sosln soslns md5sum sleep2 allinone uniq tr mesg du \
 uuencode uudecode nohup nice cmp mktemp truncate test date \
 printenv chrootuid renice \
-free losetup
+free losetup switch_root
 
 OS:=$(shell uname)
 ifeq ($(OS),Linux)