Re: [PATCH v4 2/4] initramfs: print helpful cpio error on "crc" magic

[Matthew Wilcox <willy@infradead.org>]

On Wed, Nov 10, 2021 at 01:38:48PM +0100, David Disseldorp wrote:
> Contrary to the buffer-format.rst documentation, initramfs cpio
> extraction does not support "crc" archives, which carry "070702"
> header magic. Make it a little clearer that "newc" (magic="070701") is
> the only supported cpio format, by extending the POSIX.1 ASCII
> (magic="070707") specific error message to also cover "crc" magic.

Wouldn't it be easier to just add support?  As far as I can tell from
looking at documentation, the "crc" format is the same as newc, except
that it uses some reserved bits to store the crc.  Since we ignore those
bits, we could just check for either 070701 or 070702.

> Signed-off-by: David Disseldorp <ddiss@suse.de>
> ---
>  init/initramfs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/init/initramfs.c b/init/initramfs.c
> index 2f79b3ec0b40..44e692ae4646 100644
> --- a/init/initramfs.c
> +++ b/init/initramfs.c
> @@ -258,7 +258,7 @@ static int __init do_collect(void)
>  static int __init do_header(void)
>  {
>  	if (memcmp(collected, "070701", 6)) {
> -		if (memcmp(collected, "070707", 6) == 0)
> +		if (memcmp(collected, "0707", 4) == 0)
>  			error("incorrect cpio method used: use -H newc option");
>  		else
>  			error("no cpio magic");
> -- 
> 2.31.1
>