9.24. Metadata Buffering

xfs_buf.{h,c} implements xfs_buf_t the XFS metadata buffer cache

Multi-page buffers
Buffer “pinning”
- Prevent them from being written even if “dirty”
- Transaction log must be written first
Several “private” buffer pointers
Locking, iodone semaphore for I/O waiters
Callbacks for: iodone, relse, pre-write

In-core log buffers also implemented via xfs_buf_t

This causes some oddities since they use

Separate address space from bdev