From: "Chen HanXiao" <chenhanxiao@cn.fujitsu.com>
To: 'Paolo Bonzini' <pbonzini@redhat.com>
Cc: 'Christoph Hellwig' <hch@lst.de>, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] Use SCSI command to get size of SG device
Date: Wed, 10 Oct 2012 16:33:04 +0800 [thread overview]
Message-ID: <006501cda6c1$e080f8a0$a182e9e0$@cn.fujitsu.com> (raw)
In-Reply-To: <507516D5.8040609@redhat.com>
> -----Original Message-----
> From: Paolo Bonzini [mailto:paolo.bonzini@gmail.com] On Behalf Of Paolo
> Bonzini
> Sent: Wednesday, October 10, 2012 2:34 PM
> To: Chen HanXiao
> Cc: 'Christoph Hellwig'; qemu-devel@nongnu.org
> Subject: Re: [PATCH] Use SCSI command to get size of SG device
>
> Il 10/10/2012 04:11, Chen HanXiao ha scritto:
> >> >
> >> > On Tue, Oct 09, 2012 at 05:42:01PM +0800, Chen HanXiao wrote:
> >>> > > When we use SCSI generic device as disk image, function lseek
> >>> > > could not get the size of this kind of device.
> >>> > > So try to use SCSI command Read Capacity(10) when lseek failed
> >>> > > to get the size of SCSI generic device.
> >> >
> >> > Eww, this is ugly as hell. Why would you even need the size for a
> >> > raw passthrough device?
> >
> > If we want to enable snapshot for SCSI generic device as disk image,
> > the size of SCSI generic device is needed. Function lseek could not
> > get this, SCSI command can finish the job.
> > Only when lseek failed would Read Capacity command be sent.
>
> You need to use scsi-block instead of scsi-generic. However, I don't see
how
> this can work. After the snapshot, the image will be qcow2, not raw, and
thus
> it will not support bdrv_aio_ioctl. Hence any SCSI command (for
scsi-generic)
> or any non-data SCSI command (for scsi-block) will fail.
>
That's the issue what I also encountered.
Do you mean that it is impossible for us to enable snapshot for
scsi-generic?
Or patched for qcow2 would solve this?
> Can you give an example of what exactly you are trying to do?
>
I could enable snapshot for scsi-block
device, but failed when using scsi-generic with parameter 'snapshot =on'.
The first issue is failing to get the size of SG device. So I tried to fix
it.
Command line:
-drive if=none,id=hd,file=/dev/sg2,snapshot=on \
-device virtio-scsi-pci,id=scsi --enable-kvm \
-device scsi-generic,drive=hd,id=vd1
> Paolo
Regards
next prev parent reply other threads:[~2012-10-10 8:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-09 9:42 [Qemu-devel] [PATCH] Use SCSI command to get size of SG device Chen HanXiao
2012-10-09 17:21 ` Christoph Hellwig
2012-10-10 2:11 ` Chen HanXiao
2012-10-10 6:33 ` Paolo Bonzini
2012-10-10 8:33 ` Chen HanXiao [this message]
2012-10-10 9:01 ` Paolo Bonzini
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='006501cda6c1$e080f8a0$a182e9e0$@cn.fujitsu.com' \
--to=chenhanxiao@cn.fujitsu.com \
--cc=hch@lst.de \
--cc=pbonzini@redhat.com \
--cc=qemu-devel@nongnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).