lofi(7D) compression support [PSARC/2007/569 FastTrack timeout 10/08/2007]

[Darren J Moffat]

DJM-0 I don't quite understand how this is used.

It seems that the process is like this:

Create some image file that has a filesystem on it, lets make it UFS.

# mkfile 1g /path/to/backingfile.img
# lofiadm -C gzip /path/to/backingfile.img
# lofiadm -a /path/to/backingfile.img
/dev/lofi/1
# mkfs -F ufs /dev/rlofi/1
...
# mount -F ufs /dev/lofi/1 /mnt

Is that correct ?

In otherwords unlike the crypto case, and what your man page synopsis 
suggests, the -C/-s arguments aren't things you pass in when you do a 
mapping with -a but instead they are auxiliary functions.

DJM-1 How does this interact with lofi crypto ?

(http://opensolaris.org/os/community/arc/caselog/2007/001/)

Which happens first crypto or compression (hint it needs to be 
compression otherwise it is waste of CPU resource) ?

However if my understanding of how -C and -U work it seems that the 
compression would be happening after encryption because by design it 
isn't on the fly but actually a distinct admin action (which for 
building LiveCD images is fine).

DJM-2 What is the guidance for changing the segment size ?

DJM-3 What happens if I make an lofi mapping with the default segment 
size and later map the same file with a different size ?

DJM-4 What is the minimum segment size ?

DJM-5 How big is the header section ?

The project to add encryption to lofi stalled on exactly the issue of 
the adding metadata to the image.  Since this project is adding a header 
section it seems to make sense that the crypto and compression projects 
share a metadata section.

DJM-6 How big is the index section ?

DJM-7 In the ZFS use of gzip it is possible to specify the level with 
gzip-6 being the default.   I think this case should do the same.

DJM-8 The encrypted lofi case also proposed to add a new column to the 
output to indicate if the mapping was encrypted, since this case also 
adds a new column, coordination is needed (I think we are okay here though).

Process issue:

http://opensolaris.org/os/community/arc/caselog/2007/569/  gives 404 at 
the moment.

--
Darren J Moffat