[PATCH 0/5] initmpfs: use tmpfs instead of ramfs for rootfs

[PATCH 0/5] initmpfs: use tmpfs instead of ramfs for rootfs

[Rob Landley]

Use tmpfs for rootfs when CONFIG_TMPFS=y and there's no root=.
Specify rootfstype=ramfs to get the old initramfs behavior.

The previous initramfs code provided a fairly crappy root filesystem:
didn't let you --bind mount directories out of it, reported zero
size/usage so it didn't show up in "df" and couldn't run things like
rpm that query available space before proceeding, would fill up all
available memory and panic the system if you wrote too much to it...

Using tmpfs instead provides a much better root filesystem.

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[PATCH 4/5] initmpfs: Make rootfs use tmpfs when CONFIG_TMPFS enabled.

[Rob Landley]

From: Rob Landley <rob@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 <rob@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>
@@ -600,7 +599,8 @@
 	else
 		once++;
 
-	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 = {
@@ -616,7 +616,11 @@
 	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
@@ -2787,6 +2787,10 @@
 {
 	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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