auto import from //depot/cupcake/@135843
diff --git a/toolbox/umount.c b/toolbox/umount.c
new file mode 100644
index 0000000..92c6076
--- /dev/null
+++ b/toolbox/umount.c
@@ -0,0 +1,74 @@
+
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <linux/loop.h>
+
+// FIXME - only one loop mount is supported at a time
+#define LOOP_DEVICE "/dev/block/loop0"
+
+static int is_loop_mount(const char* path)
+{
+ FILE* f;
+ int count;
+ char device[256];
+ char mount_path[256];
+ char rest[256];
+ int result = 0;
+ int path_length = strlen(path);
+
+ f = fopen("/proc/mounts", "r");
+ if (!f) {
+ fprintf(stdout, "could not open /proc/mounts\n");
+ return -1;
+ }
+
+ do {
+ count = fscanf(f, "%255s %255s %255s\n", device, mount_path, rest);
+ if (count == 3) {
+ if (strcmp(LOOP_DEVICE, device) == 0 && strcmp(path, mount_path) == 0) {
+ result = 1;
+ break;
+ }
+ }
+ } while (count == 3);
+
+ fclose(f);
+ return result;
+}
+
+int umount_main(int argc, char *argv[])
+{
+ int loop, loop_fd;
+
+ if(argc != 2) {
+ fprintf(stderr,"umount <path>\n");
+ return 1;
+ }
+
+ loop = is_loop_mount(argv[1]);
+ if(umount(argv[1])){
+ fprintf(stderr,"failed.\n");
+ return 1;
+ }
+
+ if (loop) {
+ // free the loop device
+ loop_fd = open(LOOP_DEVICE, O_RDONLY);
+ if (loop_fd < -1) {
+ perror("open loop device failed");
+ return 1;
+ }
+ if (ioctl(loop_fd, LOOP_CLR_FD, 0) < 0) {
+ perror("ioctl LOOP_CLR_FD failed");
+ return 1;
+ }
+
+ close(loop_fd);
+ }
+
+ return 0;
+}