linux-kernel - Re: [PATCH] initrd: support erofs as initrd

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Message-ID:
 <aaae4d846c4f9bf2964af2a71c78f66c9a8c2533.camel@cyberus-technology.de>
Date: Fri, 21 Mar 2025 13:26:22 +0000
From: Julian Stecklina <julian.stecklina@...erus-technology.de>
To: "thomas.weissschuh@...utronix.de" <thomas.weissschuh@...utronix.de>
CC: "hch@....de" <hch@....de>, "torvalds@...ux-foundation.org"
	<torvalds@...ux-foundation.org>, "gregkh@...uxfoundation.org"
	<gregkh@...uxfoundation.org>, "rafael@...nel.org" <rafael@...nel.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] initrd: support erofs as initrd

On Fri, 2025-03-21 at 10:16 +0100, Thomas Weißschuh wrote:
> On Thu, Mar 20, 2025 at 08:28:23PM +0100, Julian Stecklina via B4 Relay wrote:
> > From: Julian Stecklina <julian.stecklina@...erus-technology.de>
> > 
> > Add erofs detection to the initrd mount code. This allows systems to
> > boot from an erofs-based initrd in the same way as they can boot from
> > a squashfs initrd.
> > 
> > Just as squashfs initrds, erofs images as initrds are a good option
> > for systems that are memory-constrained.
> > 
> > Signed-off-by: Julian Stecklina <julian.stecklina@...erus-technology.de>
> > ---
> >  init/do_mounts_rd.c | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)
> > 
> > diff --git a/init/do_mounts_rd.c b/init/do_mounts_rd.c
> > index
> > ac021ae6e6fa78c7b7828a78ab2fa3af3611bef3..7c3f8b45b5ed2eea3c534d7f2e65608542
> > 009df5 100644
> > --- a/init/do_mounts_rd.c
> > +++ b/init/do_mounts_rd.c
> > @@ -11,6 +11,7 @@
> >  
> >  #include "do_mounts.h"
> >  #include "../fs/squashfs/squashfs_fs.h"
> > +#include "../fs/erofs/erofs_fs.h"
> >  
> >  #include <linux/decompress/generic.h>
> >  
> > @@ -47,6 +48,7 @@ static int __init crd_load(decompress_fn deco);
> >   * romfs
> >   * cramfs
> >   * squashfs
> > + * erofs
> >   * gzip
> >   * bzip2
> >   * lzma
> > @@ -63,6 +65,7 @@ identify_ramdisk_image(struct file *file, loff_t pos,
> >   struct romfs_super_block *romfsb;
> >   struct cramfs_super *cramfsb;
> >   struct squashfs_super_block *squashfsb;
> > + struct erofs_super_block *erofsb;
> >   int nblocks = -1;
> >   unsigned char *buf;
> >   const char *compress_name;
> > @@ -77,6 +80,7 @@ identify_ramdisk_image(struct file *file, loff_t pos,
> >   romfsb = (struct romfs_super_block *) buf;
> >   cramfsb = (struct cramfs_super *) buf;
> >   squashfsb = (struct squashfs_super_block *) buf;
> > + erofsb = (struct erofs_super_block *) buf;
> >   memset(buf, 0xe5, size);
> >  
> >   /*
> > @@ -165,6 +169,21 @@ identify_ramdisk_image(struct file *file, loff_t pos,
> >   goto done;
> >   }
> >  
> > + /* Try erofs */
> > + pos = (start_block * BLOCK_SIZE) + EROFS_SUPER_OFFSET;
> > + kernel_read(file, buf, size, &pos);
> > +
> > + if (erofsb->magic == EROFS_SUPER_MAGIC_V1) {
> 
> le32_to_cpu(erofsb->magic)
> 
> > + printk(KERN_NOTICE
> > +        "RAMDISK: erofs filesystem found at block %d\n",
> > +        start_block);
> > +
> > + nblocks = ((erofsb->blocks << erofsb->blkszbits) + BLOCK_SIZE - 1)
> > + >> BLOCK_SIZE_BITS;
> 
> le32_to_cpu(erofsb->blocks)
> 
> > +
> > + goto done;
> > + }
> > +
> >   printk(KERN_NOTICE
> >          "RAMDISK: Couldn't find valid RAM disk image starting at %d.\n",
> >          start_block);
> > 
> 
> This seems to be broken for cramfs and minix, too.

Great observation. Will fix! 

Julian