linux-kernel - Re: [PATCH v3 5/5] Documentation: update nfs option in filesystem/vfat.txt

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Date:	Mon, 17 Sep 2012 10:28:00 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Namjae Jeon <linkinjeon@...il.com>
Cc:	hirofumi@...l.parknet.co.jp, akpm@...ux-foundation.org,
	viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org,
	Namjae Jeon <namjae.jeon@...sung.com>,
	Ravishankar N <ravi.n1@...sung.com>,
	Amit Sahrawat <a.sahrawat@...sung.com>
Subject: Re: [PATCH v3 5/5] Documentation: update nfs option in
 filesystem/vfat.txt

On Sun, Sep 16, 2012 at 08:23:20AM -0400, Namjae Jeon wrote:
> From: Namjae Jeon <namjae.jeon@...sung.com>
> 
> update nfs option in filesystem/vfat.txt
> 
> Signed-off-by: Namjae Jeon <namjae.jeon@...sung.com>
> Signed-off-by: Ravishankar N <ravi.n1@...sung.com>
> Signed-off-by: Amit Sahrawat <a.sahrawat@...sung.com>
> ---
>  Documentation/filesystems/vfat.txt |   19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/filesystems/vfat.txt b/Documentation/filesystems/vfat.txt
> index de1e6c4..3371b8e 100644
> --- a/Documentation/filesystems/vfat.txt
> +++ b/Documentation/filesystems/vfat.txt
> @@ -141,13 +141,22 @@ discard       -- If set, issues discard/TRIM commands to the block
>  		 device when blocks are freed. This is useful for SSD devices
>  		 and sparse/thinly-provisoned LUNs.
>  
> -nfs           -- This option maintains an index (cache) of directory
> -		 inodes by i_logstart which is used by the nfs-related code to
> -		 improve look-ups.
> -
> -		 Enable this only if you want to export the FAT filesystem
> +nfs=full_unstable|limited_stable

You still want to accept just "nfs" (defaulting to "full_unstable"
behavior), for backwards compatibility.

Also I don't find this full_unstable/limited_stable terminology very
intuitive.  "stable" and "limited" could mean too many different things.

Maybe "nostale_ro|stale_rw" ?

> +	      -- Enable this only if you want to export the FAT filesystem
>  		 over NFS
>  
> +		 full_unstable:This option maintains an index (cache) of
> +		 directory inodes by i_logstart which is used by
> +		 the nfs-related code to improve look-ups.Full file operations
> +		 (read/write) over NFS is supported but with cache eviction
> +		 at NFS server, this could result in ESTALE issues.
> +
> +		 limited_stable:This options makes NFS support for FAT as
> +		 read-only and provides stable inode based on the on-disk
> +		 location of the MS-DOS directory entry.This helps in
> +		 reconstruction of the inodes in case of lookup failure,
> +		 making FAT behaviour stable with respect to ESTALE issues.

This option still scares me a little.  Maybe a little more explanation:

		This option bases the inode number and filehandle on
		the location of an file in the MS-DOS directory entry.
		This ensures that ESTALE will not be returned after a
		file is evicted from the inode cache.  However, it means
		that operations such as rename, create, and unlink could
		cause filehandles that previously pointed at one file to
		point at a different file, potentially causing data
		corruption.  For this reason, this option also mounts
		the filesystem readonly.

--b.

> +
>  <bool>: 0,1,yes,no,true,false
>  
>  TODO
> -- 
> 1.7.9.5
> 
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