Re: [PATCH] gen_init_cpio: Apply mtime supplied by user to all file types

[Masahiro Yamada]

On Wed, Dec 20, 2023 at 9:33 AM Dmitry Safonov <dima@xxxxxxxxxx> 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@xxxxxxxxxx>
> Link: https://lore.kernel.org/lkml/20181025215133.20138-1-baptiste@xxxxxxxxxx/
> Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>



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@xxxxxxxxxx>
>


-- 
Best Regards
Masahiro Yamada