misreported st_blocks (AllocationSize)

[Steve French]

Was investigating trying to fix emulation of some fallocate flags, and
was wondering how common is it for a fs to very loosely report
allocation size (st_blocks) for a file - ie the allocation sizes does
not match the allocate ranges returned by fiemap (or
SEEK_HOLE/SEEK_DATA).   Presumably there are Linux fs that coalesce
ranges on the fly so allocation sizes may be a 'guess' for some fs.

How common is this for it to be off?

-- 
Thanks,

Steve