iPXE, iSCSI and int13

[mr_jrt]

So, I'm having a looksie at the source, (and learning AT&T ASM syntax, it seems), and I'm drawn to int13_load_mbr in int13.c.

Am I reading it correctly when I read that it calls interrupt 13 function 2 with a request for 1 sector from CHS 0,0,1 from the specified drive number (0) into the buffer address (0x7c00) passed in via the variable "address", and if that succeeds, we zero-out the AX register, otherwise leave it be and save it out into the variable "status"?

I ask because that would explain why I'm seeing status 01 reported - it's read one sector (and the iSCSI side of the logging and tracing suggests this is all fine as well), but for some reason the carry flag is being set, triggering reporting as an error. I'll have to dig into the iSCSI hook to see why that would be...

Code:

Mar 11 22:27:23 192.168.60.5 ipxe: Booting from SAN device 0x80
Mar 11 22:27:23 192.168.60.5 ipxe: INT13,02 (80): Read: C/H/S 0/0/1 = LBA 00000000 <-> 0000:7c00 (count 1)
Mar 11 22:27:23 192.168.60.5 ipxe: iSCSI 0xdf214 start 28:00:00:00:00:00:00:00:01:00:00:00:00:00:00:00 in 0x200
Mar 11 22:27:23 192.168.60.5 ipxe: iSCSI 0xdf214 received PDU opcode 0x25 len 0x200
Mar 11 22:27:23 192.168.60.5 ipxe: INT13 drive 80 could not read MBR (status 01)