[PATCH v3 2/8] gen_init_cpio: support -o <output_file> parameter

David Disseldorp
2025-08-19T03:50:30Z

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 <ddiss@suse.de>
Reviewed-by: Nicolas Schier <nsc@kernel.org>
---
usr/gen_init_cpio.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
index 235bfc574e6b1..ea4b9b5fed014 100644
--- a/usr/gen_init_cpio.c
+++ b/usr/gen_init_cpio.c
@@ -1,4 +1,5 @@
// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
@@ -110,7 +111,7 @@ 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 +533,7 @@ 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_file>] <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 +570,8 @@ 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_file>: write cpio to this file instead of stdout\n",
prog);
}

@@ -611,7 +613,7 @@ int main (int argc, char *argv[])

default_mtime = time(NULL);
while (1) {
- int opt = getopt(argc, argv, "t:ch");
+ int opt = getopt(argc, argv, "t:cho:");
char *invalid;

if (opt == -1)
@@ -630,6 +632,16 @@ int main (int argc, char *argv[])
case 'c':
do_csum = true;
break;
+ case 'o':
+ outfd = open(optarg,
+ O_WRONLY | O_CREAT | O_LARGEFILE | O_TRUNC,
+ 0600);
+ if (outfd < 0) {
+ fprintf(stderr, "failed to open %s\n", optarg);
+ usage(argv[0]);
+ exit(1);
+ }
+ break;
case 'h':
case '?':
usage(argv[0]);
--
2.43.0