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

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

[Namjae Jeon]

From: Namjae Jeon <namjae.jeon@samsung.com>

update nfs option in filesystem/vfat.txt

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Ravishankar N <ravi.n1@samsung.com>
Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.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
+	      -- 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.
+
 <bool>: 0,1,yes,no,true,false
 
 TODO
-- 
1.7.9.5

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

[J. Bruce Fields]

On Sun, Sep 16, 2012 at 08:23:20AM -0400, Namjae Jeon wrote:
> From: Namjae Jeon <namjae.jeon@samsung.com>
> 
> update nfs option in filesystem/vfat.txt
> 
> Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
> Signed-off-by: Ravishankar N <ravi.n1@samsung.com>
> Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.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
> 

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

[Namjae Jeon]

2012/9/17, J. Bruce Fields <bfields@fieldses.org>:
> On Sun, Sep 16, 2012 at 08:23:20AM -0400, Namjae Jeon wrote:
>> From: Namjae Jeon <namjae.jeon@samsung.com>
>>
>> update nfs option in filesystem/vfat.txt
>>
>> Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
>> Signed-off-by: Ravishankar N <ravi.n1@samsung.com>
>> Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.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
>
Hi Bruce.
> You still want to accept just "nfs" (defaulting to "full_unstable"
> behavior), for backwards compatibility.
Agree. I will consider backwards compatibilty as your opinion.
>
> 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" ?
Yes, It would be better!
>
>> +	      -- 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.
Okay, I will update.

Thanks for your review!
>
> --b.
>
>> +
>>  <bool>: 0,1,yes,no,true,false
>>
>>  TODO
>> --
>> 1.7.9.5
>>
>