bcon: early support for file logging

It if possible to log to a regular file now, similar to how the swapfile
code operates.  Blockconsole will call bmap() for all blocks, build up
an extent map and then write raw to the block device.  The extend map is
used to get the correct disk addresses for the file.

Like swapfile, this is broken on btrfs and similar cow filesystems.
Blockconsole still requires 512B writes to work, so 4k drives may also
cause problems.  And most importantly I never tested anything funny -
using the same file twice, etc.

Signed-off-by: Joern Engel <joern@logfs.org>
2 files changed