From: Rob Landley <r...@landley.net>

Conditionally call the appropriate fs_init function and fill_super functions.
Add a use once guard to shmem_init() to simply succeed on a second call.

(Note that IS_ENABLED() is a compile time constant so dead code elimination
removes unused function calls when CONFIG_TMPFS is disabled.)

Signed-off-by: Rob Landley <r...@landley.net>
---

 init/do_mounts.c |   10 ++++++++--
 mm/shmem.c       |    4 ++++
 2 files changed, 12 insertions(+), 2 deletions(-)

--- initold/init/do_mounts.c    2013-06-27 00:02:26.283442977 -0500
+++ initwork/init/do_mounts.c   2013-06-27 00:45:21.599550312 -0500
@@ -27,6 +27,7 @@
 #include <linux/fs_struct.h>
 #include <linux/slab.h>
 #include <linux/ramfs.h>
+#include <linux/shmem_fs.h>
 
 #include <linux/nfs_fs.h>
 #include <linux/nfs_fs_sb.h>
@@ -598,7 +597,8 @@
        if (test_and_set_bit(1, &once))
                return ERR_PTR(-ENODEV);
 
-       return mount_nodev(fs_type, flags, data, ramfs_fill_super);
+       return mount_nodev(fs_type, flags, data,
+               IS_ENABLED(CONFIG_TMPFS) ? shmem_fill_super : ramfs_fill_super);
 }
 
 static struct file_system_type rootfs_fs_type = {
@@ -614,7 +614,11 @@
        if (err)
                return err;
 
-       err = init_ramfs_fs();
+       if (IS_ENABLED(CONFIG_TMPFS))
+               err = shmem_init();
+       else
+               err = init_ramfs_fs();
+
        if (err)
                unregister_filesystem(&rootfs_fs_type);
 
--- initold/mm/shmem.c  2013-06-25 13:09:22.215743137 -0500
+++ initwork/mm/shmem.c 2013-06-27 00:16:58.195479317 -0500
@@ -2816,6 +2816,10 @@
 {
        int error;
 
+       /* If rootfs called this, don't re-init */
+       if (shmem_inode_cachep)
+               return 0;
+
        error = bdi_init(&shmem_backing_dev_info);
        if (error)
                goto out4;
--
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