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xen-devel
Re: [Xen-devel] RFC: Xen cdrom haldaemon
Could the haldaemon's work be pushed into blkback in the kernel?
-- Keir
On 5/9/07 17:43, "Pat Campbell" <plc@xxxxxxxxxx> wrote:
> Hi,
>
> I have found that the DOM0 CDROM device returns a stale disk
> size if a CD is changed while any application has the device open.
>
> Test scenerio: ( Don't need XEN for this )
> Two shell processes
> Shell A runs simple test program with an arg to
> open the cd for reading
> report media size using lseek(0, SEEK_END)
> then enter a sleep loop leaving FD open
> In Shell B
> eject
> insert a different CD
> eject -t,
> run simple test progran, no arg
> ( size is still what was reported in shell A)
> Kill Shell A test CD process
> Run test CD process again, now you should have the
> correct size
>
> Simple test program, cdrom-test.c, has been attached.
>
> I did enter a defect against the Linux kernel about this but
> was unable to convince them it was their defect.
>
> If we put Xen in the mix, say installing a FV Redhat system
> from physical CD media you will have two CDROM device file
> descriptors open. One in blkback and the other in QEMU.
> When you get to CD #2 you won't be able to complete the
> install as the total disk size has not been updated for
> the larger CD #2, stays at the smaller CD #1 size.
>
> You can get the QEMU descriptor closed by using xen-store
> writes but none effect the blkback FD and there is no
> way, that I have found, to effect ALL open Xen related FDs on
> that device.
>
> I have created a proof of concept patch for 3.1 that addresses the
> above issue by causing all VMs, FV and PV, to close thier open
> pyhsical CDROM file descriptors when the device door is opened. File
> descriptors are re-opened when the door is closed AND a CD was
> inserted.
>
> The basic flow of the patch is:
>
> Kernel:
> blkback driver:
> if block device is a physical cdrom then
> Add media_present=1 into xenstore backend/vbd
> for this device
> Place a xenstore watch on media_present
>
> watch_handler
> if watch token is media_present
> read value
> if 0 then close block device fd
> if 1 then re-open block device fd
>
> Any access with fd closed results in EACCESS error
>
> qemu
> if block device is a cdrom
> Place a xenstore watch on media_present
> watch_handler
> if watch token is media_present
> read value
> if 0 then close block device
> if 1 then re-open block device and set media_changed
>
> Any access with fd closed results in EACCESS error
>
> xend
> Starts XEN HalDaemon process
>
> XEN HalDaemon
> Registers event callback for HALD events
> callback handler
> gets device major/minor numbers
> for each vbd in xenstore
> if matching major and minor
> if add_event ( cdrom door closed with media )
> xenstore write 1 to vbd/media_present
> else ( cddrom door open )
> xenstore write 0 to vbd/media_present
>
> I am just learning python, could use a python guy to enhance and
> generalize.
>
> With my patch applied I was able to install RHEL5 from the 5 CD set as
> well as a WIN2003 server from multi CD media.
>
> The patch is attached. Patch still needs some work but I would like
> some feedback before going further down this path. Is this something
> that fits into the current and near future architecture and might be
> considered for addition?
>
> Thanks in advance
>
> Pat
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel
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