db(3) removal and lastlogx

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

Hi all,
there is a bit mechnical work left to remove db(3) dependencies e.g. for
the password database, but that's mostly that. The last real consume of
the db(3) API in libc is the lastlogx handling in utmpx. Basically, this
logs a record in a file indexed by uid. I can think of three different
approaches for dealing with this:

(1) Just use a sparse file. This requires by far the least amount of
code, just some verification logic for a file header and writing to "uid
* size of entry". Writes should be short enough to ensure atomic writes
even on NFS. Same for reads. No manual locking needed.

(2) Implement a simple hierachical byte-level index, e.g. start by a
table of 256 off_t entries, index with the LSB continue. For read
hitting an off_t of 0 means the entry doesn't exist, for write get a
byte range lock for that area, append a new index page / the entry to
the file and use a single write to update it. Provide iterator interface
to find all entries in the file. Somewhat more involved, but not too
much.

(3) Implement on-disk PATRICA lookup. Still much simpler than b-tree,
but also more work than (2).

Comments?

Joerg