[PATCH-RFC] init: simplify initrd code (was Re: [PATCH RESEND 00/62] initrd: remove classic initrd support).

[David Disseldorp]

Hi Nicolas,

On Thu, 25 Sep 2025 15:10:56 +0200, nschichan at freebox.fr wrote:

> From: Nicolas Schichan <nschichan at freebox.fr>
> 
> - drop prompt_ramdisk and ramdisk_start kernel parameters
> - drop compression support
> - drop image autodetection, the whole /initrd.image content is now
>   copied into /dev/ram0
> - remove rd_load_disk() which doesn't seem to be used anywhere.
> 
> There is now no more limitation on the type of initrd filesystem that
> can be loaded since the code trying to guess the initrd filesystem
> size is gone (the whole /initrd.image file is used).
> 
> A few global variables in do_mounts_rd.c are now put as local
> variables in rd_load_image() since they do not need to be visible
> outside this function.
> ---
> 
> Hello,
> 
> Hopefully my email config is now better and reaches gmail users
> correctly.
> 
> The patch below could probably split in a few patches, but I think
> this simplify the code greatly without removing the functionality we
> depend on (and this allows now to use EROFS initrd images).
> 
> Coupled with keeping the function populate_initrd_image() in
> init/initramfs.c, this will keep what we need from the initrd code.
> 
> This removes support of loading bzip/gz/xz/... compressed images as
> well, not sure if many user depend on this feature anymore.
> 
> No signoff because I'm only seeking comments about those changes right
> now.
> 
>  init/do_mounts.h    |   2 -
>  init/do_mounts_rd.c | 243 +-------------------------------------------
>  2 files changed, 4 insertions(+), 241 deletions(-)

This seems like a reasonable improvement to me. FWIW, one alternative
approach to clean up the FS specific code here was proposed by Al:
https://lore.kernel.org/all/20250321020826.GB2023217@ZenIV/

...
> diff --git a/init/do_mounts_rd.c b/init/do_mounts_rd.c
> index ac021ae6e6fa..5a69ff43f5ee 100644
> --- a/init/do_mounts_rd.c
> +++ b/init/do_mounts_rd.c
> @@ -14,173 +14,9 @@
>  
>  #include <linux/decompress/generic.h>
>  
> -static struct file *in_file, *out_file;
> -static loff_t in_pos, out_pos;
> -
> -static int __init prompt_ramdisk(char *str)
> -{
> -	pr_warn("ignoring the deprecated prompt_ramdisk= option\n");
> -	return 1;
> -}
> -__setup("prompt_ramdisk=", prompt_ramdisk);
> -
> -int __initdata rd_image_start;		/* starting block # of image */
> -
> -static int __init ramdisk_start_setup(char *str)
> -{
> -	rd_image_start = simple_strtol(str,NULL,0);
> -	return 1;
> -}
> -__setup("ramdisk_start=", ramdisk_start_setup);

There are a couple of other places that mention these parameters, which
should also be cleaned up.

...
>  static unsigned long nr_blocks(struct file *file)
>  {
> -	struct inode *inode = file->f_mapping->host;
> -
> -	if (!S_ISBLK(inode->i_mode))
> -		return 0;
> -	return i_size_read(inode) >> 10;
> +	return i_size_read(file->f_mapping->host) >> 10;

This should be >> BLOCK_SIZE_BITS, and dropped as a wrapper function
IMO.