I just read the comment in fs/efs_fs.h properly for the first time,
and things are now much clearer. I think.
So, is _this_ correct?
* We're indirect, so we need to start looking in the
* indirect extents.
* EFS indirect extents are really doubly indirect:
* inode->di_u.di_extents (1st level extents) refers to
* contiguous blocks of extents (2nd level extents). The
* block of these 2nd level extents contain direct extents (or
* 3rd level extents). So, for each indirect extent in
* di_u.di_extents, we need to get a block of 2nd-level
* extents, get a block from one of the 2nd-level extents, and
* then check the extents in that final block -- which, at
* long last, contains direct extents.
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