[Qemu-devel] The reversion of hot adding a storage disk to Linux guest.

[Shu Ming <shuming@linux.vnet.ibm.com>]

Hi,
   I am testing the hot plug of scsi disk to the KVM Linux guest with 
the following command.

   [root@kvm-rhel-01 bin]# ./virsh qemu-monitor-command RHEL6.1-C 
"pci_add auto storage file=/nfs/images/storage1-qcow2.img,if=scsi"
OK domian 0, bus 0, slot 7, function 0
   [root@kvm-rhel-01 bin]# lspci
...
00:05.0 SCSI storage controller: Red Hat, Inc Virtio block device
00:06.0 RAM memory: Red Hat, Inc Virtio memory balloon
00:07.0 SCSI storage controller: LSI Logic / Symbios Logic 53c895a 
<---new deviced added

  in the KVM guest:
   [root@RHEL6 ~]#cat /proc/scsi/scsi
Attached devices:
Host: scsi1 Channel: 00 Id:  00 Lun: 00
   Vendor:  QEMU    Model: QEMU DVD-ROM    Rev:  1.0.
    Type:    CD-ROM
Host: scsi2  Channel: 00  Id:  00 Lun: 00
    Vendor:  QEMU    Model: QEMU HARDDISK    Rev:  1.0.
     Type:      Direct-Access        ANSI    SCSI revision:  05 
<------new scsi disk attached

   The command successfully created a HBA device in the guest and also a 
scsi disk was enumerated under the HBA device.  My next request is to 
hot detach the scsi disk from the HBA device, not necessarily detach the 
HBA device.  That is to emulate the swapping  out of the scsi disk from 
a physical machine and to release the image file in the backend.  
Because the scsi disk is not PCI device,  "pci_del" command can not be 
used in this case.  Can we have a way to send some commands to notice 
the HBA device to offline the scsi disk?  By that way, HBA device can do 
some cleanup in their driver to fully offline the scsi disk.

BTW: In the linux guest, we can do "echo "scsi remove-single-device 2 0 
0 0" > /proc/scsi/scsi" to disable the disk.  But I don't think it is 
fully removed, because you can bring it back again by "echo "scsi 
add-single-device 2 0 0 0" > /proc/scsi/scsi"

-- 
Shu Ming<shuming@linux.vnet.ibm.com>
IBM China Systems and Technology Laboratory