Disable scsi disk requests in QEMU when using virtio-blk device

[Arnabjyoti Kalita]

Hello all,

Is it possible to disable scsi disk requests being generated by the
guest when using a virtio-blk device?

I am starting the guest in KVM mode using the below command line-

sudo ./qemu-system-x86_64 -m 1024 --machine pc-i440fx-2.5 -cpu
qemu64,-kvmclock,-kvm_pv_eoi
-enable-kvm -netdev tap,id=tap1,ifname=tap0,script=no,downscript=no
-device virtio-net-pci,netdev=tap1,mac=00:00:00:00:00:00 -object
filter-replay,id=replay,netdev=tap1
-drive 
file=~/os_images_for_qemu/ubuntu-16.04-desktop-amd64.qcow2,format=qcow2,if=none,id=img-direct
-device virtio-blk-pci,drive=img-direct

I keep seeing some interrupts being generated as a result of scsi
requests, which I really want to disable.

GDB backtrace output -

bt
#0  blk_update_request (req=0x88003548e450, error=0, nr_bytes=8)
at /build/linux-Ay7j_C/linux-4.4.0/block/blk-core.c:2568
#1  0x815ad873 in scsi_end_request (req=0x88003548e450,
error=, bytes=, bidi_bytes=) at /build/linux-Ay7j_C/linux-4.4.0/drivers/scsi/scsi_lib.c:695
#2  0x815b09c4 in scsi_io_completion (cmd=0x88003548e450,
good_bytes=) at
/build/linux-Ay7j_C/linux-4.4.0/drivers/scsi/scsi_lib.c:915
#3  0x815a7b4f in scsi_finish_command (cmd=0x880002237a80)
at /build/linux-Ay7j_C/linux-4.4.0/drivers/scsi/scsi.c:607
#4  0x815b0244 in scsi_softirq_done (rq=) at
/build/linux-Ay7j_C/linux-4.4.0/drivers/scsi/scsi_lib.c:1640
#5  0x813c1d37 in blk_done_softirq (h=) at
/build/linux-Ay7j_C/linux-4.4.0/block/blk-softirq.c:35
#6  0x810859a1 in __do_softirq () at
/build/linux-Ay7j_C/linux-4.4.0/kernel/softirq.c:273
#7  0x81085ca3 in invoke_softirq () at
/build/linux-Ay7j_C/linux-4.4.0/kernel/softirq.c:350

Is there a command line switch or parameter that will disable
generation of scsi requests and its associated interrupts? The scsi
module is built into the guest kernel (kernel version 4.4.0).

Note: I am using QEMU version 5.0.1 and my host and target
architecture is x86_64.

Thank you very much.

Best Regards,
Arnab

USB SD Card reader, Windows Host, Linux Guest

[Brendan Simon (eTRIX)]

Hi,

Does anyone know of qemu supports usb SD card reader on Windows host, so 
I can access my SD card as /dev/sd* on my debian linux guest ??


I'm using qemu 6.0.0 (via MSYS2 package install) specifing the command 
line arguemnts:


    -device qemu-xhci -device usb-host,vendorid=0x14CD,productid=0x168A

The vendor and product IDs were obtained using `usbview` (also an MSYS2 
package).  I couldn't find those IDs by looking at Hardware IDs in 
Device Manager properties of the selected device, but usbview did show them.


However I cannot get the device to show up in linux (dmesg output, ls 
/dev/*), and if I insert an SD card Windows captures and mounts the volume.


I am using a laptop with

Thanks any help and suggestions,
Brendan.

Re: Disable scsi disk requests in QEMU when using virtio-blk device

[Thomas Huth]

On 18/07/2021 15.37, Arnabjyoti Kalita wrote:

Hello all,

Is it possible to disable scsi disk requests being generated by the
guest when using a virtio-blk device?

I am starting the guest in KVM mode using the below command line-

sudo ./qemu-system-x86_64 -m 1024 --machine pc-i440fx-2.5 -cpu
qemu64,-kvmclock,-kvm_pv_eoi
-enable-kvm -netdev tap,id=tap1,ifname=tap0,script=no,downscript=no
-device virtio-net-pci,netdev=tap1,mac=00:00:00:00:00:00 -object
filter-replay,id=replay,netdev=tap1
-drive 
file=~/os_images_for_qemu/ubuntu-16.04-desktop-amd64.qcow2,format=qcow2,if=none,id=img-direct
-device virtio-blk-pci,drive=img-direct


Try to replace the last line with:

 -device virtio-blk-pci,drive=img-direct,scsi=off

Generally, you can see a list of valid options for a device by running QEMU 
with something like:


 qemu-system-x86_64 -device virtio-blk-pci,help

 HTH,
  Thomas