Re: [dm-devel] [RFC] dm-bow working prototype

[Alasdair G Kergon]

On Wed, Oct 24, 2018 at 03:24:29PM -0400, Mikulas Patocka wrote:
> What about allocating a big file, using the FIEMAP ioctl to find the 

For reference, dmfilemapd in the lvm2 tree (in daemons/) uses FIEMAP
(in libdm/libdm-stats.c) for monitoring I/O by file.

> If you decide that rollback is no longer needed, you just unload the 
> snapshot target and delete the big file. If you decide that you want to 
> rollback, you can use the snapshot merge functionality (or you can write a 
> userspace utility that does offline merge).
 
There's some old code from Mark McLoughlin for userspace snapshot merging here:
  https://people.gnome.org/~markmc/code/merge-dm-snapshot.c

Alasdair