Re: [PATCH] btrfs: Add "barrier" option to support "-o remount,barrier"

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

On Thu, 2 Jan 2014 16:41:03 +0100, David Sterba wrote:
> On Thu, Dec 26, 2013 at 02:45:10PM +0800, Qu Wenruo wrote:
>> Btrfs can be remounted without barrier, but there is no "barrier" option
>> so nobody can remount btrfs back with barrier on. Only umount and
>> mount again can re-enable barrier.(Quite awkward)
> Ok for adding the mount option.
>
>> Reported-by: Daniel Blueman <daniel@quora.org>
>> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
>> ---
>>   Documentation/filesystems/btrfs.txt | 6 ++++++
>>   fs/btrfs/super.c                    | 8 +++++++-
>>   2 files changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/filesystems/btrfs.txt b/Documentation/filesystems/btrfs.txt
>> index 5dd282d..f6f71d6 100644
>> --- a/Documentation/filesystems/btrfs.txt
>> +++ b/Documentation/filesystems/btrfs.txt
>> @@ -51,6 +51,12 @@ Unless otherwise specified, all options default to off.
>>   	defrag process.  Works best for small files; Not well suited for
>>   	large database workloads.
>>   
>> +  barrier
>> +	Enable the use of block layer write barriers.  Write barriers ensure
>> +	that certain IOs make it through the device cache and are on persistent
>> +	storage.
>> +	Barriers are enabled by default.
> There's the 'nobarrier' option already, I think it's better to keep the
> pairing option documentation at one place and mark the default one with (*).
>
> Related to that, there should imho be a pairing option for every mount
> option where it makes sense, so all the combinations work through
> remount.
>
> The defaults do not need to be listed via btrfs_show_options, ie. keep
> the output same as it is now.
>
>
> david
>
Thanks for pointing out these problem.

This makes sense.Like space_cache and nospace_cache follows the way you 
mentioned,
but most other options just followed the alphabet order, and a lot of
pairing is missing.

I'll try to add all the missingpairing and unify mount options in the 
document.

Qu