Re: [Qemu-devel] [PATCH v2 3/3] raw-posix: Re-open host CD-ROM after media change

[Stefan Hajnoczi]

On Tue, Apr 5, 2011 at 7:41 AM, Amit Shah <address@hidden> wrote:
> On (Mon) 04 Apr 2011 [16:09:05], Stefan Hajnoczi wrote:
>> On Mon, Apr 4, 2011 at 2:49 PM, Avi Kivity <address@hidden> wrote:
>> > On 04/04/2011 04:38 PM, Anthony Liguori wrote:
>> >>
>> >> On 04/04/2011 08:22 AM, Avi Kivity wrote:
>> >>>
>> >>> On 04/03/2011 02:57 PM, Stefan Hajnoczi wrote:
>> >>>>
>> >>>> In order for media change to work with Linux host CD-ROM it is
>> >>>> necessary to reopen the file (otherwise the inode size will not
>> >>>> refresh, this is an issue with existing kernels).
>> >>>>
>> >>>
>> >>> Maybe we should fix the bug in Linux (and backport as necessary)?
>> >>>
>> >>> I think cd-rom assignment is sufficiently obscure that we can require a
>> >>> fixed kernel instead of providing a workaround.
>> >>
>> >> Do reads fail after CD change?  Or do they succeed and the size is just
>> >> reported incorrectly?
>> >>
>> >> If it's the later, I'd agree that it needs fixing in the kernel.  If it's
>> >> the former, I'd say it's clearly a feature.
>> >>
>> >
>> > Even if it's a documented or intentional feature, we can add an ioctl to
>> > "refresh" the device with up-to-date data.
>>
>> It's possible to fix this in the kernel.  I just haven't written the
>> patch yet.  The inode size needs to be updated when the new medium is
>> detected.
>>
>> I haven't tested but I suspect reads within the size of the previous
>> medium will succeed.  But if the new medium is larger then reads
>> beyond the old medium size will fail.
>
> See http://www.spinics.net/lists/linux-scsi/msg51504.html

I don't think that patch updates the block inode size.  We'd need to
call fs/block_dev.c:revalidate_disk() instead of directly calling
cdi->disk->fops->revalidate_disk(cdi->disk).
fs/block_dev.c:revalidate_disk() calls check_disk_size_change(), which
will update the inode size.

Here are the steps to reproduce the issue: https://lkml.org/lkml/2011/3/23/156

Stefan