df,find_mount_point: optionally don't ignore rootfs

Signed-off-by: Lauri Kasanen <curaga@operamail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

coreutils/df.c

@@ -160,7 +160,7 @@ int df_main(int argc UNUSED_PARAM, char **argv)
 			}
 
 			/* GNU coreutils 6.10 skips certain mounts, try to be compatible.  */
-			if (strcmp(device, "rootfs") == 0)
+			if (ENABLE_FEATURE_SKIP_ROOTFS && strcmp(device, "rootfs") == 0)
 				continue;
 
 #ifdef WHY_WE_DO_IT_FOR_DEV_ROOT_ONLY

libbb/Config.src

@@ -161,6 +161,25 @@ config FEATURE_COPYBUF_KB
 	  Bigger buffers will be allocated with mmap, with fallback to 4 kb
 	  stack buffer if mmap fails.
 
+config FEATURE_SKIP_ROOTFS
+	bool "Skip rootfs in mount table"
+	default y
+	help
+	  Ignore rootfs entry in mount table.
+
+	  In Linux, kernel has a special filesystem, rootfs, which is initially
+	  mounted on /. It contains initramfs data, if kernel is configured
+	  to have one. Usually, another file system is mounted over / early
+	  in boot process, and therefore most tools which manipulate
+	  mount table, such as df, will skip rootfs entry.
+
+	  However, some systems do not mount anything on /.
+	  If you need to configure busybox for one of these systems,
+	  you may find useful to turn this option off to make df show
+	  initramfs statistic.
+
+	  Otherwise, choose Y.
+
 config MONOTONIC_SYSCALL
 	bool "Use clock_gettime(CLOCK_MONOTONIC) syscall"
 	default n

libbb/find_mount_point.c

@@ -43,7 +43,7 @@ struct mntent* FAST_FUNC find_mount_point(const char *name, int subdir_too)
 		/* rootfs mount in Linux 2.6 exists always,
 		 * and it makes sense to always ignore it.
 		 * Otherwise people can't reference their "real" root! */
-		if (strcmp(mountEntry->mnt_fsname, "rootfs") == 0)
+		if (ENABLE_FEATURE_SKIP_ROOTFS && strcmp(mountEntry->mnt_fsname, "rootfs") == 0)
 			continue;
 
 		if (strcmp(name, mountEntry->mnt_dir) == 0