[PATCH] initramfs: Allow rootfs to use tmpfs instead of ramfs

[Al Boldi <a1426z@gawab.com>]

Replugs rootfs to use tmpfs instead of ramfs as a Kconfig option.

This patch is based on John Zielinski's 
http://marc.theaimsgroup.com/?l=linux-kernel&m=107013630212011&w=4 patch.

Modified for 2.6.17.

RunTime tested on i386.

This trivial patch should go into 2.6.18.

Cc: <stable@kernel.org>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Andrew Morton <akpm@osdl.org>
Cc: John Zielinski <grim@undead.cc>
Signed-off-by: Al Boldi <a1426z@gawab.com>

---
--- a/drivers/block/Kconfig	2006-07-30 16:44:59.000000000 +0300
+++ b/drivers/block/Kconfig	2006-07-30 16:45:53.000000000 +0300
@@ -412,6 +412,22 @@ config BLK_DEV_INITRD
 	  If RAM disk support (BLK_DEV_RAM) is also included, this
 	  also enables initial RAM disk (initrd) support.
 
+config SHM_ROOTFS
+	bool "Use tmpfs (shm) instead of ramfs for rootfs"
+	depends on BLK_DEV_INITRD
+	default n
+	select TMPFS
+	select SHMEM
+	help
+	  This option switches rootfs so that it uses tmpfs rather than ramfs
+	  for it's file storage.  This makes rootfs swappable so having a large
+	  initrd or initramfs image won't eat up valuable RAM.
+
+config RAMFS_ROOTFS
+	bool 
+	depends on !SHM_ROOTFS
+	default y
+	select RAMFS
 
 config CDROM_PKTCDVD
 	tristate "Packet writing on CD/DVD media"
--- a/fs/Kconfig	2006-07-30 16:45:25.000000000 +0300
+++ b/fs/Kconfig	2006-07-30 16:46:36.000000000 +0300
@@ -853,7 +853,7 @@ config HUGETLB_PAGE
 	def_bool HUGETLBFS
 
 config RAMFS
-	bool
+	tristate "Ramfs file system support"
 	default y
 	---help---
 	  Ramfs is a file system which keeps all files in RAM. It allows
--- a/fs/ramfs/inode.c	2006-07-30 16:45:37.000000000 +0300
+++ b/fs/ramfs/inode.c	2006-07-30 16:46:36.000000000 +0300
@@ -191,22 +191,27 @@ struct super_block *ramfs_get_sb(struct 
 	return get_sb_nodev(fs_type, flags, data, ramfs_fill_super);
 }
 
+#ifdef CONFIG_RAMFS_ROOTFS
 static struct super_block *rootfs_get_sb(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data)
 {
 	return get_sb_nodev(fs_type, flags|MS_NOUSER, data, ramfs_fill_super);
 }
+#endif
 
 static struct file_system_type ramfs_fs_type = {
 	.name		= "ramfs",
 	.get_sb		= ramfs_get_sb,
 	.kill_sb	= kill_litter_super,
 };
+
+#ifdef CONFIG_RAMFS_ROOTFS
 static struct file_system_type rootfs_fs_type = {
 	.name		= "rootfs",
 	.get_sb		= rootfs_get_sb,
 	.kill_sb	= kill_litter_super,
 };
+#endif
 
 static int __init init_ramfs_fs(void)
 {
@@ -221,9 +226,11 @@ static void __exit exit_ramfs_fs(void)
 module_init(init_ramfs_fs)
 module_exit(exit_ramfs_fs)
 
+#ifdef CONFIG_RAMFS_ROOTFS
 int __init init_rootfs(void)
 {
 	return register_filesystem(&rootfs_fs_type);
 }
+#endif
 
 MODULE_LICENSE("GPL");
--- a/mm/shmem.c	2006-07-30 16:45:54.000000000 +0300
+++ b/mm/shmem.c	2006-07-30 16:47:11.000000000 +0300
@@ -2123,7 +2123,7 @@ failed:
 	return err;
 }
 
-static struct kmem_cache *shmem_inode_cachep;
+static struct kmem_cache *shmem_inode_cachep = NULL;
 
 static struct inode *shmem_alloc_inode(struct super_block *sb)
 {
@@ -2156,11 +2156,13 @@ static void init_once(void *foo, struct 
 
 static int init_inodecache(void)
 {
-	shmem_inode_cachep = kmem_cache_create("shmem_inode_cache",
-				sizeof(struct shmem_inode_info),
-				0, 0, init_once, NULL);
-	if (shmem_inode_cachep == NULL)
-		return -ENOMEM;
+	if(!shmem_inode_cachep) {
+		shmem_inode_cachep = kmem_cache_create("shmem_inode_cache",
+					sizeof(struct shmem_inode_info),
+					0, 0, init_once, NULL);
+		if (shmem_inode_cachep == NULL)
+			return -ENOMEM;
+	}
 	return 0;
 }
 
@@ -2345,6 +2347,27 @@ put_memory:
 	return ERR_PTR(error);
 }
 
+#ifdef CONFIG_SHM_ROOTFS
+static struct super_block *rootfs_get_sb(struct file_system_type *fs_type,
+	int flags, const char *dev_name, void *data)
+{
+	return get_sb_single(fs_type, flags, data, shmem_fill_super);
+}
+
+static struct file_system_type rootfs_fs_type = {
+	.name		= "rootfs",
+	.get_sb		= rootfs_get_sb,
+	.kill_sb	= kill_litter_super,
+};
+
+int __init init_rootfs(void)
+{
+	if (init_inodecache())
+		panic("Can't initialize shm inode cache");
+	return register_filesystem(&rootfs_fs_type);
+}
+#endif
+
 /*
  * shmem_zero_setup - setup a shared anonymous mapping
  *

--