linux-ext4 - Re: Which features should I implement in my ext4 reader?

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Message-ID: <CACyNnZManY_k3SB1-p4mQ8Z1+9B=VAdfXU7bWsFVHDsHV6KyUQ@mail.gmail.com>
Date:	Wed, 14 Aug 2013 07:06:44 +0200
From:	Felipe Monteiro de Carvalho <felipemonteiro.carvalho@...il.com>
To:	linux-ext4@...r.kernel.org
Subject: Re: Which features should I implement in my ext4 reader?

Hello,

Did my last message go through? Just wondering if it was lost ...

thanks,

Felipe Monteiro de Carvalho

On Mon, Aug 12, 2013 at 5:38 PM, Felipe Monteiro de Carvalho
<felipemonteiro.carvalho@...il.com> wrote:
> Hello,
>
> Thanks to the help here I have essentially finished my ext4 reader =)
> At least it can read ext4 filesystems with these features, which is
> what I found when using Ubuntu and Mageia LInux:
>
>    EXT4_FEATURE_INCOMPAT_JOURNAL_DEV    = $0008; // Journal device */
>    EXT4_FEATURE_INCOMPAT_META_BG        = $0010;
>    EXT4_FEATURE_INCOMPAT_EXTENTS        = $0040; // extents support */
>    EXT4_FEATURE_INCOMPAT_FLEX_BG        = $0200;
>    EXT4_FEATURE_INCOMPAT_64BIT          = $0080;
>
> Some features seam to not require any extra care for my reader:
>
>    EXT4_FEATURE_INCOMPAT_COMPRESSION    = $0001;
>    EXT4_FEATURE_INCOMPAT_FILETYPE       = $0002;
>    EXT4_FEATURE_INCOMPAT_RECOVER        = $0004; // Needs recovery */
>    EXT4_FEATURE_INCOMPAT_BG_USE_META_CSUM= $2000; // use crc32c for bg */
>
> But I now wonder about these features:
>
>    EXT4_FEATURE_INCOMPAT_MMP            = $0100;
>    EXT4_FEATURE_INCOMPAT_EA_INODE       = $0400; // EA in inode */
>    EXT4_FEATURE_INCOMPAT_DIRDATA        = $1000; // data in dirent */
>    EXT4_FEATURE_INCOMPAT_LARGEDIR       = $4000; // >2GB or 3-lvl htree */
>    EXT4_FEATURE_INCOMPAT_INLINEDATA     = $8000; // data in inode */
>
> Could anyone comment how common is the use of those features and if
> they are already stable and in production usage (I read that they were
> under development in 2011)?
>
> And also which ones require an active work for a reader application to
> implement. As I already found out that FLEX_BG does not require active
> work to be supported despite being in the INCOMPAT list...
>
> From the description I'm pretty sure that at least DIRDATA and
> INLINEDATA would require adjustments in my software. But I wonder if
> they are already being used and stable, etc, and if it is a good idea
> to work on supporting them.
>
> thanks, =)
> --
> Felipe Monteiro de Carvalho



-- 
Felipe Monteiro de Carvalho
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