FS types whose size are not known at compile time

[travis1829]

In Lfs,

• Based on the max number of inodes n,
  • The size of the in-memory Imap should be (n + 255) / 256 * 4 bytes to store the mapping for all inodes.
• Based on the total number of segments s of the disk,
  • The size of the in-memory SegTable should be (s + 7) / 8 bytes to store the mapping for all segments.

The problem is, n or s are not known at compile time, and hence, the size of the in-memory Imap or SegTable are also not known at compile time. Note that the Ufs also had a similar problem and solved this by limiting the max number of inodes to 200 for all disks.

To solve this, we should

• Allocate the Imap and SegTable at a page instead of placing it on the Kernel. (At booting or every time we mount a disk)
• Make the Imap or SegTable big enough so that any n or s should work.
  • We should have a reasonable limit for n or s.
  • This could be a small waste of memory if n or b is actually small for the disk.