[9fans] segfree() - more details?

[lucio@proxima.alt.za]

The rather tantalising:

          Segfree tells the system that it may free any physical mem-
          ory within the span [va, va+len), but leaves that portion of
          the process's address space valid.  The system will not free
          any memory outside that span, and may not free all or even
          any of the specified memory.  If free'd memory is later ref-
          erenced, it will be initialized as appropriate for the seg-
          ment type.  For example data and text segments will be read
          from the executable file, and bss segments will be filled
          with zero bytes.

in segattach(2) suggests that there is some mechanism to associate
disk file portions with memory segments (that being what Unix's MMAP
does, roughly), but falls short of explaining how this association is
established.  I presume there is documentation for this elsewhere that
ought to be mentioned in the above.

Also, I'm too dense to grasp the exact intent of segfree(2) as implied
in the above description, but I'm sure once I understand it I'll be
able to make use of it in my efforts to make Plan 9 understand ELF
directly.  So if anyone can point me to the right place, I'd greatly
appreciate it.

I have Nemo's "commentary" that has proved invaluable to my
understanding of the Plan 9 kernel, but I always have to find it by
inspection because its filename is not very self-explanatory.  I guess
I ought to change that, but I'm the conservative type: does anyone
remember its name?

++L