On 2014-09-23 10:23, Tobias Holst wrote:
> If it is unknown, which of these options have been used at btrfs
> creation time - is it possible to check the state of these options
> afterwards on a mounted or unmounted filesystem?
>
>
> 2014-09-23 15:38 GMT+02:00 Austin S Hemmelgarn <ahferroin7@gmail.com
> <mailto:ahferroin7@gmail.com>>:
>
>     Well, running 'mkfs.btrfs -O list-all' with 3.16 btrfs-progs gives
>     the following list of features:
>     mixed-bg                - mixed data and metadata block groups
>     extref                  - increased hard-link limit per file to 65536
>     raid56                  - raid56 extended format
>     skinny-metadata         - reduced size metadata extent refs
>     no-holes                - no explicit hole extents for files
>
I don't think there is a specific tool for doing this, but some of them 
do show up in dmesg, for example skinny-metadata shows up as a mention 
of the FS having skinny extents.