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

[Al Boldi <a1426z@gawab.com>]

Hugh Dickins wrote:
> On Sun, 30 Jul 2006, Al Boldi wrote:
> > Replugs rootfs to use tmpfs instead of ramfs as a Kconfig option.
>
> Why?  Looking further down we see what you should have explained here:
> > + This option switches rootfs so that it uses tmpfs rather than ramfs
> > + for its file storage.  This makes rootfs swappable so having a large
> > + initrd or initramfs image won't eat up valuable RAM.
>
> Now, I'm far from an expert on initramfs and early userspace, but my
> understanding is that the "init" of a (properly designed) initramfs
> would pretty much "rm -rf" everything in the initramfs before passing
> control to the final "init".  So (almost?) no valuable RAM is eaten
> up, nor the less valuable swap if you do extend this to tmpfs (unless
> something gets left open, which I think should not be the case).
>
> So I'm inclined to say that this patch is simply unnecessary.  But
> if people who know better think it's a good thing, I've no objection
> (though I've not tried it): the Kconfiggery looks more likely to
> provoke argument than the tmpfs/ramfs mods.
>
> > 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.
>
> Well...
>
> > Cc: <stable@kernel.org>
> > Cc: Chris Wright <chrisw@sous-sol.org>
>
> Umm, the -stable tree doesn't usually take enhancements,
> even if you think it's a very stable enhancement.
>
> > 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
>
> Please say TMPFS_ROOTFS rather than SHM_ROOTFS throughout.

Ok.

> > +	bool "Use tmpfs (shm) instead of ramfs for rootfs"
> > +	depends on BLK_DEV_INITRD
> > +	default n
> > +	select TMPFS
> > +	select SHMEM
>
> Selects can be troublesome, but you may well have decided right.
>
> > +	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
>
>               its

Yes.

> > +	  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;
>
> No need to initialize static variables to 0 (or is someone going to
> raise the spectre of NULL being non-0 on some future architecture?)

Don't know.

> >  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) {
>
>         if (shmem_inode_cachep == NULL) {
> is more consistent with the nearby style

Ok.

> > +		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");
>
>                                         "tmpfs inode cache"
>                                      or "shmem inode cache"

Yes, shmem.

> > +	return register_filesystem(&rootfs_fs_type);
> > +}
> > +#endif
> > +
> >  /*
> >   * shmem_zero_setup - setup a shared anonymous mapping
> >   *

Thanks for your review!

--
Al

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