Re: [OSS-Tools] [PATCH dt-utils 08/13] state: keep backward compatibility

[Roland Hieber <rhi@pengutronix.de>]

On Mon, Sep 30, 2019 at 09:26:08AM +0200, Ulrich Ölmann wrote:
> Introduce the new build time option '--enable-state-backward-compatibility' to
> port the following barebox commit.
> 
> NOTE: This changes barebox-state's default behaviour.
> 
> | commit 480cde1b22831febacc2a8ab91dfe99d2e5be8e9
> | Author: Juergen Borleis <jbe@pengutronix.de>
> | Date:   Tue Aug 15 15:46:31 2017 +0200
> |
> |     state: keep backward compatibility
> |
> |     Previous 'state' variable set variants do not know and use metadata. The
> |     'direct' storage backend's read function honors this, but not its
> |     counterpart the write function. This makes an update of the 'state'
> |     variable set impossible.
> |     This change makes backward compatibility explicit, else it complains in
> |     the read function as well. With some more debug output it helps the
> |     developer to do things right.
> |
> |     Signed-off-by: Juergen Borleis <jbe@pengutronix.de>
> |     Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> 
> Signed-off-by: Ulrich Ölmann <u.oelmann@pengutronix.de>
> ---
>  configure.ac                              | 28 +++++++++++++++--------
>  src/barebox-state.c                       |  2 ++
>  src/barebox-state/backend_bucket_direct.c | 28 +++++++++++++++--------
>  3 files changed, 40 insertions(+), 18 deletions(-)
> 
> diff --git a/configure.ac b/configure.ac
> index 777f4956ba5f..04c2226625c1 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -32,6 +32,15 @@ AS_IF([test "x$enable_debug" = "xyes"], [
>          AC_DEFINE(DEBUG, [1], [Debug messages.])
>  ])
>  
> +AC_ARG_ENABLE([state-backward-compatibility],
> +        AS_HELP_STRING([--enable-state-backward-compatibility], [keep the 'direct' storage backend backward compatible @<:@default=disabled@:>@]),
> +        [], [enable_state_backward_compatibility=no])
> +AS_IF([test "x${enable_state_backward_compatibility}" = "xyes"], [
> +        AC_DEFINE(CONFIG_STATE_BACKWARD_COMPATIBLE, [1], ['direct' storage backend backward compatibility.])
> +], [
> +        AC_DEFINE(CONFIG_STATE_BACKWARD_COMPATIBLE, [0])
> +])
> +
>  AC_CHECK_FUNCS([__secure_getenv secure_getenv])
>  
>  my_CFLAGS="-Wall \
> @@ -53,15 +62,16 @@ AC_MSG_RESULT([
>          $PACKAGE $VERSION
>          =====
>  
> -        prefix:                 ${prefix}
> -        sysconfdir:             ${sysconfdir}
> -        libdir:                 ${libdir}
> -        includedir:             ${includedir}
> +        prefix:                         ${prefix}
> +        sysconfdir:                     ${sysconfdir}
> +        libdir:                         ${libdir}
> +        includedir:                     ${includedir}
>  
> -        compiler:               ${CC}
> -        cflags:                 ${CFLAGS}
> -        ldflags:                ${LDFLAGS}
> +        compiler:                       ${CC}
> +        cflags:                         ${CFLAGS}
> +        ldflags:                        ${LDFLAGS}
>  
> -        logging:                ${enable_logging}
> -        debug:                  ${enable_debug}
> +        logging:                        ${enable_logging}
> +        debug:                          ${enable_debug}
> +        state-backward-compatibility:   ${enable_state_backward_compatibility}
>  ])

It's good to have this as a build-time option. I have just sent a
barebox patch to clarify that behaviour [1], and I would suggest the
following fixup here:

-        AS_HELP_STRING([--enable-state-backward-compatibility], [keep the 'direct' storage backend backward compatible @<:@default=disabled@:>@]),
+        AS_HELP_STRING([--enable-state-backward-compatibility], [barebox-state: when using the 'direct' storage backend, keep the on-disk format readable by barebox <= v2016.08.0 @<:@default=disabled@:>@])

[1]: https://www.mail-archive.com/barebox@lists.infradead.org/msg32865.html

> diff --git a/src/barebox-state.c b/src/barebox-state.c
> index 946a8dba6d8c..6b166bfe6e02 100644
> --- a/src/barebox-state.c
> +++ b/src/barebox-state.c
> @@ -439,6 +439,8 @@ int main(int argc, char *argv[])
>  			exit(0);
>  		case OPT_VERSION:
>  			printf(PACKAGE_STRING "\n");
> +			printf("Configured with build-time option '--%s-state-backward-compatibility'.\n",
> +			       (CONFIG_STATE_BACKWARD_COMPATIBLE) ? "enable" : "disable");

Oh yes, that's very reasonable too.

 - Roland

>  			exit(0);
>  		case 'g':
>  			sg = xzalloc(sizeof(*sg));
> diff --git a/src/barebox-state/backend_bucket_direct.c b/src/barebox-state/backend_bucket_direct.c
> index 5b5506be002e..4522f0170f3d 100644
> --- a/src/barebox-state/backend_bucket_direct.c
> +++ b/src/barebox-state/backend_bucket_direct.c
> @@ -75,6 +75,11 @@ static int state_backend_bucket_direct_read(struct state_backend_storage_bucket
>  	} else {
>  		if (meta.magic != ~0 && !!meta.magic)
>  			bucket->wrong_magic = 1;
> +		if (!IS_ENABLED(CONFIG_STATE_BACKWARD_COMPATIBLE)) {
> +			dev_err(direct->dev, "No meta data header found\n");
> +			dev_dbg(direct->dev, "Enable backward compatibility or increase stride size\n");
> +			return -EINVAL;
> +		}
>  		read_len = direct->max_size;
>  		if (lseek(direct->fd, direct->offset, SEEK_SET) !=
>  		    direct->offset) {
> @@ -110,20 +115,25 @@ static int state_backend_bucket_direct_write(struct state_backend_storage_bucket
>  	int ret;
>  	struct state_backend_storage_bucket_direct_meta meta;
>  
> -	if (len > direct->max_size - sizeof(meta))
> -		return -E2BIG;
> -
>  	if (lseek(direct->fd, direct->offset, SEEK_SET) != direct->offset) {
>  		dev_err(direct->dev, "Failed to seek file, %d\n", -errno);
>  		return -errno;
>  	}
>  
> -	meta.magic = direct_magic;
> -	meta.written_length = len;
> -	ret = write_full(direct->fd, &meta, sizeof(meta));
> -	if (ret < 0) {
> -		dev_err(direct->dev, "Failed to write metadata to file, %d\n", ret);
> -		return ret;
> +	/* write the meta data only if there is head room */
> +	if (len <= direct->max_size - sizeof(meta)) {
> +		meta.magic = direct_magic;
> +		meta.written_length = len;
> +		ret = write_full(direct->fd, &meta, sizeof(meta));
> +		if (ret < 0) {
> +			dev_err(direct->dev, "Failed to write metadata to file, %d\n", ret);
> +			return ret;
> +		}
> +	} else {
> +		if (!IS_ENABLED(CONFIG_STATE_BACKWARD_COMPATIBLE)) {
> +			dev_dbg(direct->dev, "Too small stride size: must skip metadata! Increase stride size\n");
> +			return -EINVAL;
> +		}
>  	}
>  
>  	ret = write_full(direct->fd, buf, len);
> -- 
> 2.23.0
> 
> 
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> OSS-Tools@pengutronix.de

-- 
Roland Hieber                     | r.hieber@pengutronix.de     |
Pengutronix e.K.                  | https://www.pengutronix.de/ |
Peiner Str. 6-8, 31137 Hildesheim | Phone: +49-5121-206917-5086 |
Amtsgericht Hildesheim, HRA 2686  | Fax:   +49-5121-206917-5555 |

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