linux-kernel - Re: [PATCH] Make JFFS2 endianness configurable

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Date:   Fri, 2 Nov 2018 08:45:43 +0000
From:   Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
To:     "nkela@...co.com" <nkela@...co.com>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>
CC:     "rod@...tby.id.au" <rod@...tby.id.au>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "xe-linux-external@...co.com" <xe-linux-external@...co.com>
Subject: Re: [PATCH] Make JFFS2 endianness configurable

On Thu, 2018-11-01 at 15:56 -0700, Nikunj Kela wrote:
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.
> 
> 
> This patch allows the endianness of the JFSS2 filesystem to be
> specified by config options.
> 
> It defaults to native-endian (the previously hard-coded option).
> 
> Some architectures benefit from having a single known endianness
> of JFFS2 filesystem (for data, not executables) independent of the
> endianness of the processor (ARM processors can be switched to either
> endianness at run-time).

I like this too. I have on several occasions needed to mount a JFFS2 BE on
my PC. This saves me from having to hack the src.

 Jocke

> 
> This patch is taken from:
> http://www.infradead.org/pipermail/linux-mtd/2006-January/014717.html
> 
> Cc: xe-linux-external@...co.com
> Signed-off-by: Rod Whitby <rod@...tby.id.au>
> Signed-off-by: Nikunj Kela <nkela@...co.com>
> ---
>  fs/jffs2/Kconfig    | 25 +++++++++++++++++++++++++
>  fs/jffs2/nodelist.h |  8 +++-----
>  2 files changed, 28 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/jffs2/Kconfig b/fs/jffs2/Kconfig
> index ad850c5bf2ca..86e93fbc9d74 100644
> --- a/fs/jffs2/Kconfig
> +++ b/fs/jffs2/Kconfig
> @@ -182,3 +182,28 @@ config JFFS2_CMODE_FAVOURLZO
>           decompression) at the expense of size.
> 
>  endchoice
> +
> +choice
> +       prompt "JFFS2 endianness"
> +       default JFFS2_NATIVE_ENDIAN
> +       depends on JFFS2_FS
> +       help
> +         You can set here the default endianness of JFFS2 from
> +         the available options. Do not touch if unsure.
> +
> +config JFFS2_NATIVE_ENDIAN
> +       bool "native endian"
> +       help
> +         Uses a native endian bytestream.
> +
> +config JFFS2_BIG_ENDIAN
> +       bool "big endian"
> +       help
> +         Uses a big endian bytestream.
> +
> +config JFFS2_LITTLE_ENDIAN
> +       bool "little endian"
> +       help
> +         Uses a little endian bytestream.
> +
> +endchoice
> diff --git a/fs/jffs2/nodelist.h b/fs/jffs2/nodelist.h
> index 0637271f3770..a1ebf04f217c 100644
> --- a/fs/jffs2/nodelist.h
> +++ b/fs/jffs2/nodelist.h
> @@ -27,12 +27,10 @@
>  #include "os-linux.h"
>  #endif
> 
> -#define JFFS2_NATIVE_ENDIAN
> -
>  /* Note we handle mode bits conversion from JFFS2 (i.e. Linux) to/from
>     whatever OS we're actually running on here too. */
> 
> -#if defined(JFFS2_NATIVE_ENDIAN)
> +#if defined(CONFIG_JFFS2_NATIVE_ENDIAN)
>  #define cpu_to_je16(x) ((jint16_t){x})
>  #define cpu_to_je32(x) ((jint32_t){x})
>  #define cpu_to_jemode(x) ((jmode_t){os_to_jffs2_mode(x)})
> @@ -43,7 +41,7 @@
>  #define je16_to_cpu(x) ((x).v16)
>  #define je32_to_cpu(x) ((x).v32)
>  #define jemode_to_cpu(x) (jffs2_to_os_mode((x).m))
> -#elif defined(JFFS2_BIG_ENDIAN)
> +#elif defined(CONFIG_JFFS2_BIG_ENDIAN)
>  #define cpu_to_je16(x) ((jint16_t){cpu_to_be16(x)})
>  #define cpu_to_je32(x) ((jint32_t){cpu_to_be32(x)})
>  #define cpu_to_jemode(x) ((jmode_t){cpu_to_be32(os_to_jffs2_mode(x))})
> @@ -54,7 +52,7 @@
>  #define je16_to_cpu(x) (be16_to_cpu(x.v16))
>  #define je32_to_cpu(x) (be32_to_cpu(x.v32))
>  #define jemode_to_cpu(x) (be32_to_cpu(jffs2_to_os_mode((x).m)))
> -#elif defined(JFFS2_LITTLE_ENDIAN)
> +#elif defined(CONFIG_JFFS2_LITTLE_ENDIAN)
>  #define cpu_to_je16(x) ((jint16_t){cpu_to_le16(x)})
>  #define cpu_to_je32(x) ((jint32_t){cpu_to_le32(x)})
>  #define cpu_to_jemode(x) ((jmode_t){cpu_to_le32(os_to_jffs2_mode(x))})
> --
> 2.19.1
> 
> 
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/

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