On Fri, Jan 15, 2016 at 09:49:58AM +0800, Qu Wenruo wrote:

David Sterba wrote on 2016/01/14 17:00 +0100:

quoted

On Tue, Jan 12, 2016 at 10:05:11AM +0800, Qu Wenruo wrote:

quoted

'Norecovery' mount option is almost a standard for all other
filesystems, including f2fs, ext4, gfs2, nilfs2, and xfs.
And since current 'recovery' mount option for btrfs is too generic, it's
better to change btrfs 'recovery' to 'usebackuproot' and then we can
safely add 'norecovery' and 'nologreplay' mount option for btrfs.

The patch itself is not huge and already tested by others since v2.
Only mount option name is changing during all these version changes.

So we have some kind of consensus about the options, but I think you
need to split the patches further.

It's never a bad idea to split patches :)

My comment was motivated by the patch that introduced nologreplay and
norecovery in one go, although the functionality is logically separate
from the user's POV.

quoted

* the new option 'nologreplay'
* keep 'usebackuproot' as a new alias for 'recovery' (with the
   deprecation warning)
* new 'norecovery' that switches on 'nologreplay' and 'nousebackuproot'
   (ie. the desired "no writes")

There is a case in remount, when we start with 'ro,nologreplay' then
remount with just 'ro', the log should be replayed. The other
combinations should be easy. I haven't looked at the patch if it's
implemented that way though.

For that case, even remount with -o remount,ro the nologreplay mount 
option won't be erased.
That's why we added a lot of "noXXXX" mount option, or we can't disable 
some feature by remount.

Yeah, I've realized that later that we need the 'logreplay' option to
achieve the readonly transition to the replayed state.

And since I didn't add such "logreplay" mount option intentionally, so 
there is no way to replay log unless umount the fs and mount it without 
"nologreplay" again.

I'll update the patchset soon and hopes it can catch the rc1 merge window.

Yeah, I'd like to see it 4.5 as well, the topic has been discussed
enough and the implementation is simple.