Re: [PATCH 2/4] btrfs: use sb state to print space_cache mount option

[Josef Bacik <josef@toxicpanda.com>]

On 9/17/20 2:13 PM, Boris Burkov wrote:
> To make the contents of /proc/mounts better match the actual state of
> the file system, base the display of the space cache mount options off
> the contents of the super block rather than the last mount options
> passed in. Since there are many scenarios where the mount will ignore a
> space cache option, simply showing the passed in option is misleading.
> 
> For example, if we mount with -o remount,space_cache=v2 on a read-write
> file system without an existing free space tree, we won't build a free
> space tree, but /proc/mounts will read space_cache=v2 (until we mount
> again and it goes away)
> 
> There is already mount logic based on the super block's cache_generation
> and free space tree flag that helps decide a consistent setting for the
> space cache options, so we just bring those further to the fore. For
> free space tree, the flag is already consistent, so we just switch mount
> option display to use it. cache_generation is not always reliably set
> correctly, so we ensure that cache_generation > 0 iff the file system
> is using space_cache v1. This requires committing a transaction on any
> mount which changes whether we are using v1. (v1->nospace_cache, v1->v2,
> nospace_cache->v1, v2->v1).
> 
> References: https://github.com/btrfs/btrfs-todo/issues/5
> Signed-off-by: Boris Burkov <boris@bur.io>

Dave already took this, but next time I'd prefer if we'd keep logical changes 
separate.  So one patch to change /proc/mounts, one patch to deal with clearing 
the free space generation field if we're not using it.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef