Help with struct disk_op_s and block drives

[Daniel Castro]

Hello,
I am working on the PV block drivers for Xen.

I am in the point where I must write to my PV ring the requests and responses.
I need a little help to understand how this works :)
The operation comes wrapped in this structure:
struct disk_op_s {
    u64 lba;
    void *buf_fl;
    struct drive_s *drive_g;
    u16 count;
lba is the sector I need to read or write to, right?
count is how many sectors I am going to move, right?
buf_fl is the pointer to the buffer where I will put the info in case
of write, or I will get the info in case of read, right?
command is either read or write.
drive_s contains the descriptor of the drive.

How does seabios handle more than one drive? My case, right now is
only one drive but there will be more.

Thanks for the help,

Daniel