Disk I/O
This lecture focuses on disk I/O and buffers.
A Disk Device (Virtio-Disk) transfers blocks of size 1024B. A sector is the smallest addressable unit by physical media. This is generally smaller than a block.
The second block in xv6 contains metadata about how many blocks are allocated and other stuff.
Reads and writes can be done by virtio_disk_rw(buf_ptr, 0) or
virtio_disk_rw(buf_ptr, 1) which either does a read or write.