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

From: Alasdair G Kergon
Date: Wed Oct 24 2018 - 20:01:35 EST

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: