vfs_altfsid & dm_fsid

[Aurelien Degremont - Stagiaire <degremont@xxxxxxxxxxx>]

Hello,

Still trying to figure out the dmapi/xfs code, here is my new problem :).

I wonder what should be set in dmfsid (dm_inode_to_fh/dm_fh_to_inode in 
dmapiops) field.
This is my guess :
In XFS, this value is filled with the vfs_altfsid which seems to be an 
unique ID (for the XFS file system on this machine) set up at filesystem 
creation. The other filesystems (especially ext3) do not seem to own an 
equivalent value. (If right, in your opinion, what could be used instead ? )

What are the precise constrains of this field, for DMAPI ? Apparently, 
it is used to identify each filesystem registered on DMAPI, whatever its 
filesystem type is. So how find a unique ID if sereval filesystems (not 
 partitions) are used ?


More explanation about dmapi_kern.h stuff would be greatly appreciated 
:) (I've understood the global system but the details, especially the 
constrains aren't explained)


TIA.

Aurélien