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Message-ID: <CAK7LNAQcocw+MtQE3DUoQNyhcWO3dSUDuBCxwTzi7YqdBFpNcw@mail.gmail.com>
Date: Sat, 23 Dec 2023 19:49:11 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Dmitry Safonov <dima@...sta.com>
Cc: Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>,
Baptiste Covolato <baptiste@...sta.com>, Benjamin Gray <bgray@...ux.ibm.com>,
Kevin Mitchell <kevmitch@...sta.com>, linux-kbuild@...r.kernel.org,
linux-kernel@...r.kernel.org, Dmitry Safonov <0x7f454c46@...il.com>
Subject: Re: [PATCH] gen_init_cpio: Apply mtime supplied by user to all file types
On Wed, Dec 20, 2023 at 9:33 AM Dmitry Safonov <dima@...sta.com> wrote:
>
> Currently gen_init_cpio -d <timestamp> is applied to symlinks,
> directories and special files. These files are created by
> gen_init_cpio from their description. Without <timestamp> option
> current time(NULL) is used. And regular files that go in initramfs
> are created before cpio generation, so their mtime(s) are preserved.
>
> This is usually not an issue as reproducible builds should rebuild
> everything in the distribution, including binaries, configs and whatever
> other regular files may find their way into kernel's initramfs.
>
> On the other hand, gen_initramfs.sh usage claims:
> > -d <date> Use date for all file mtime values
>
> Ar Arista initramfs files are managed with version control system
> that preserves mtime. Those are configs, boot parameters, init scripts,
> version files, platform-specific files, probably some others, too.
>
> While it's certainly possible to work this around by copying the file
> into temp directory and adjusting mtime prior to gen_init_cpio call,
> I don't see why it needs workarounds.
>
> The intended user of -d <date> option is the one that needs to create
> a reproducible build, see commit a8b8017c34fe ("initramfs: Use
> KBUILD_BUILD_TIMESTAMP for generated entries"). If a user wants
> the build reproduction, they use -d <date>, which can be set on all
> types of files, without surprising exceptions and workarounds.
> Let's KISS here and just apply the time that user specified
> with -d option.
>
> Based-on-a-patch-by: Baptiste Covolato <baptiste@...sta.com>
> Link: https://lore.kernel.org/lkml/20181025215133.20138-1-baptiste@arista.com/
> Signed-off-by: Dmitry Safonov <dima@...sta.com>
Applied to linux-kbuild.
Thanks.
> ---
> usr/gen_init_cpio.c | 33 +++++++++++++++++++++------------
> 1 file changed, 21 insertions(+), 12 deletions(-)
>
> diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
> index 61230532fef1..edcdb8abfa31 100644
> --- a/usr/gen_init_cpio.c
> +++ b/usr/gen_init_cpio.c
> @@ -27,6 +27,7 @@
> static unsigned int offset;
> static unsigned int ino = 721;
> static time_t default_mtime;
> +static bool do_file_mtime;
> static bool do_csum = false;
>
> struct file_handler {
> @@ -329,6 +330,7 @@ static int cpio_mkfile(const char *name, const char *location,
> int file;
> int retval;
> int rc = -1;
> + time_t mtime;
> int namesize;
> unsigned int i;
> uint32_t csum = 0;
> @@ -347,16 +349,21 @@ static int cpio_mkfile(const char *name, const char *location,
> goto error;
> }
>
> - if (buf.st_mtime > 0xffffffff) {
> - fprintf(stderr, "%s: Timestamp exceeds maximum cpio timestamp, clipping.\n",
> - location);
> - buf.st_mtime = 0xffffffff;
> - }
> + if (do_file_mtime) {
> + mtime = default_mtime;
> + } else {
> + mtime = buf.st_mtime;
> + if (mtime > 0xffffffff) {
> + fprintf(stderr, "%s: Timestamp exceeds maximum cpio timestamp, clipping.\n",
> + location);
> + mtime = 0xffffffff;
> + }
>
> - if (buf.st_mtime < 0) {
> - fprintf(stderr, "%s: Timestamp negative, clipping.\n",
> - location);
> - buf.st_mtime = 0;
> + if (mtime < 0) {
> + fprintf(stderr, "%s: Timestamp negative, clipping.\n",
> + location);
> + mtime = 0;
> + }
> }
>
> if (buf.st_size > 0xffffffff) {
> @@ -387,7 +394,7 @@ static int cpio_mkfile(const char *name, const char *location,
> (long) uid, /* uid */
> (long) gid, /* gid */
> nlinks, /* nlink */
> - (long) buf.st_mtime, /* mtime */
> + (long) mtime, /* mtime */
> size, /* filesize */
> 3, /* major */
> 1, /* minor */
> @@ -536,8 +543,9 @@ static void usage(const char *prog)
> "file /sbin/kinit /usr/src/klibc/kinit/kinit 0755 0 0\n"
> "\n"
> "<timestamp> is time in seconds since Epoch that will be used\n"
> - "as mtime for symlinks, special files and directories. The default\n"
> - "is to use the current time for these entries.\n"
> + "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",
> prog);
> }
> @@ -594,6 +602,7 @@ int main (int argc, char *argv[])
> usage(argv[0]);
> exit(1);
> }
> + do_file_mtime = true;
> break;
> case 'c':
> do_csum = true;
>
> ---
> base-commit: 55cb5f43689d7a9ea5bf35ef050f12334f197347
> change-id: 20231219-gen_init_cpio-reproducible-99c707d8e66c
>
> Best regards,
> --
> Dmitry Safonov <dima@...sta.com>
>
--
Best Regards
Masahiro Yamada
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