[Qemu-devel] Film scanner and large transfer sizes with pvscsi

[Jarkko Lavinen]

I am trying to get a Minolta Multi Pro film scanner to work in a Qemu VM with 
pvsci interface and linux as both guest and host (kernel 4.4).

The scanning stalls at VM with no error in the scanning program but I can spot 
out of memory error when initiating a transfer at host side log. The host has 
many gigabytes of free memory, though. And the same scanning program works 
alright at host side.

When using 022077 SCSI logging level at host (max level or error and timeouts). 
I can see on the host log:

  ...
  [sg6] tag#0 CDB: Test Unit Ready 00 00 00 00 00 00
  [sg6] sg_cmd_done: pack_id=0, res=0x0
  [sg6] sg_finish_rem_req: res_used=0
  [sg6] sg_remove_scat: k_use_sg=0

  [sg6] sg_ioctl: cmd=0x2285 (SG_IO)
  [sg6] sg_common_write:  scsi opcode=0x28, cmd_size=10 (0x28 is READ cmd)
  [sg6] sg_start_req: dxfer_len=30408704
  [sg6] sg_build_indirect: buff_size=30408704, blk_size=30408704
  [sg6] sg_build_indirect: k=0, num=32768, ret_sz=32768
  ...
  [sg6] sg_build_indirect: k=127, num=32768, ret_sz=32768
  [sg6] sg_build_indirect: k_use_sg=128, rem_sz=26214400
  [sg6] sg_common_write: start_req err=-12
  [sg6] sg_finish_rem_req: res_used=0
  [sg6] sg_remove_scat: k_use_sg=128
  [sg6] sg_remove_scat: k=0, pg=0xffffea0000802800
  ...
  [sg6] sg_remove_scat: k=127, pg=0xffffea00052e8600
  [sg6] sg_ioctl: cmd=0x2285

Two problems here. There is an error in host kernel side and the error does not
propagate to the guest side scanning program.

Jarkko Lavinen