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From:   Andreas Dilger <adilger@dilger.ca>
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Subject: Re: Exporting ext4-specific information through fsinfo attributes
Date:   Tue, 21 Apr 2020 16:07:43 -0600
In-Reply-To: <2504712.1587485842@warthog.procyon.org.uk>
Cc:     "Darrick J. Wong" <darrick.wong@oracle.com>,
        Eric Biggers <ebiggers@kernel.org>,
        Theodore Ts'o <tytso@mit.edu>,
        Ext4 Developers List <linux-ext4@vger.kernel.org>
To:     David Howells <dhowells@redhat.com>
References: <20200401151837.GB56931@magnolia>
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On Apr 21, 2020, at 10:17 AM, David Howells <dhowells@redhat.com> wrote:
> 
> Darrick J. Wong <darrick.wong@oracle.com> wrote:
> 
>> The entire superblock as a binary blob? :)
> 
> How about the attached?  Please forgive the duplication of struct
> ext4_super_block into the test program, but it's not in the UAPI.

I think (hope?) Darrick was joking?

At least IMHO, exporting the whole superblock as a binary blob is not
a great user interface.  I guess it has the benefit of allowing access
to various non-standard fields without accessing the device directly.
Kind of like SCSI mode pages, but that can get ugly quickly...

I can definitely get behind adding generic properties like the ones
you list below.

> 
> David
> ---
> fsinfo: Add support to ext4
> 
> Add support to ext4, including the following:
> 
> (1) FSINFO_ATTR_SUPPORTS: Information about supported STATX attributes and
>     support for ioctls like FS_IOC_[GS]ETFLAGS and FS_IOC_FS[GS]ETXATTR.
> 
> (2) FSINFO_ATTR_FEATURES: Information about features supported by an ext4
>     filesystem, such as whether version counting, birth time and name case
>     folding are in operation.
> 
> (3) FSINFO_ATTR_VOLUME_NAME: The volume name from the superblock.
> 
> (4) FSINFO_ATTR_EXT4_SUPERBLOCK: The entirety of the on disk-format
>     superblock record as an opaque blob.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: "Theodore Ts'o" <tytso@mit.edu>
> cc: Andreas Dilger <adilger.kernel@dilger.ca>
> cc: "Darrick J. Wong" <darrick.wong@oracle.com>
> cc: Eric Biggers <ebiggers@kernel.org>
> cc: linux-ext4@vger.kernel.org

Cheers, Andreas


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