Subject: Re: [PATCH v2 2/7] gen_init_cpio: support -o <output_path> parameter

From: Nicolas Schier <[email-masked]>
Date: Mon, 18 Aug 2025 20:40:34 +0200

On Thu, Aug 14, 2025 at 03:18:00PM +1000, David Disseldorp wrote:
> This is another preparatory change to allow for reflink-optimized
> cpio archives with file data written / cloned via copy_file_range().
> The output file is truncated prior to write, so that it maps to
> usr/gen_initramfs.sh usage. It may make sense to offer an append option
> in future, for easier archive concatenation.
> 
> Signed-off-by: David Disseldorp <[email-masked]>
> ---
>  usr/gen_init_cpio.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
> index d8779fe4b8f1f..563594a0662a6 100644
> --- a/usr/gen_init_cpio.c
> +++ b/usr/gen_init_cpio.c
> @@ -110,7 +110,7 @@ static int cpio_trailer(void)
>  	 || push_pad(padlen(offset, 512)) < 0)
>  		return -1;
>  
> -	return 0;
> +	return fsync(outfd);
>  }
>  
>  static int cpio_mkslink(const char *name, const char *target,
> @@ -532,7 +532,7 @@ static int cpio_mkfile_line(const char *line)
>  static void usage(const char *prog)
>  {
>  	fprintf(stderr, "Usage:\n"
> -		"\t%s [-t <timestamp>] [-c] <cpio_list>\n"
> +		"\t%s [-t <timestamp>] [-c] [-o <output_path>] <cpio_list>\n"
>  		"\n"
>  		"<cpio_list> is a file containing newline separated entries that\n"
>  		"describe the files to be included in the initramfs archive:\n"
> @@ -569,7 +569,8 @@ static void usage(const char *prog)
>  		"as mtime for symlinks, directories, regular and special files.\n"
>  		"The default is to use the current time for all files, but\n"
>  		"preserve modification time for regular files.\n"
> -		"-c: calculate and store 32-bit checksums for file data.\n",
> +		"-c: calculate and store 32-bit checksums for file data.\n"
> +		"<output_path>: write cpio to this file instead of stdout\n",

gen_init_cpio writes only a single output file (instead of multiple
files to an output directory), I'd suggest to name the parameter just
'file' or 'output_file'.

I'd like to see the the '... -o ...' patch right after this one.

For compilability, I had to add

#define _LARGEFILE64_SOURCE

or

#define _GNU_SOURCE

as you do in the next patch, in order to get O_LARGEFILE defined.

Kind regards,
Nicolas