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

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

No other comments? Anyway,  I think we need a way to hot unplug a 
storage disk from the guest totally exactly liking to remove a disk 
physically.  After that unplugging, linux guest can not  bring back the 
disk by any command.
On 2012-1-12 16:57, Shu Ming wrote:
> 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