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Re: [Qemu-devel] [PATCH 1/2] iscsi: Use bs->sg for everything else than
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] iscsi: Use bs->sg for everything else than disks |
Date: |
Wed, 5 Mar 2014 16:41:20 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
Am 05.03.2014 um 16:33 hat Benoît Canet geschrieben:
> The Wednesday 05 Mar 2014 à 16:00:48 (+0100), Kevin Wolf wrote :
> > The current iscsi block driver code makes the rather arbitrary decision
> > that TYPE_MEDIUM_CHANGER and TYPE_TAPE devices have bs->sg = 1 and all
> > other device types are disks.
> >
> > Instead of this, check for TYPE_DISK to expose the disk interface and
> > make everything else bs->sg = 1. In particular, this includes devices
> > with TYPE_STORAGE_ARRAY, which is what LUN 0 of an iscsi target is.
> > (See https://bugzilla.redhat.com/show_bug.cgi?id=1067784 for the exact
> > scenario.)
> >
> > Signed-off-by: Kevin Wolf <address@hidden>
> > ---
> > block/iscsi.c | 9 ++++-----
> > 1 file changed, 4 insertions(+), 5 deletions(-)
> >
> > diff --git a/block/iscsi.c b/block/iscsi.c
> > index 0a15f53..b490e98 100644
> > --- a/block/iscsi.c
> > +++ b/block/iscsi.c
> > @@ -1231,12 +1231,11 @@ static int iscsi_open(BlockDriverState *bs, QDict
> > *options, int flags,
> > bs->total_sectors = sector_lun2qemu(iscsilun->num_blocks, iscsilun);
> > bs->request_alignment = iscsilun->block_size;
> >
> > - /* Medium changer or tape. We dont have any emulation for this so this
> > must
> > - * be sg ioctl compatible. We force it to be sg, otherwise qemu will
> > try
> > - * to read from the device to guess the image format.
> > + /* We don't have any emulation for devices other than disks and
> > CD-ROMs, so
> > + * this must be sg ioctl compatible. We force it to be sg, otherwise
> > qemu
> > + * will try to read from the device to guess the image format.
> > */
> > - if (iscsilun->type == TYPE_MEDIUM_CHANGER ||
> > - iscsilun->type == TYPE_TAPE) {
> > + if (iscsilun->type != TYPE_DISK && iscsilun->type != TYPE_ROM) {
> I don't understand you are talking about type TYPE_STORAGE_ARRAY in the commit
> message but testing against TYPE_ROM and they are not the same.
> Maybe a comment explaining the role of TYPE_ROM would give a clue to non scsi
> savy persons like me.
TYPE_STORAGE_ARRAY is what exposed the bug (see the Bugzilla reference).
It was previously bs->sg = 0, but becomes now bs->sg = 1. The reason for
this is that the usual block layer operations only work on disks (i.e.
hard disks = TYPE_DISK and CD-ROM drives = TYPE_ROM), so for all the
rest we can only expose a generic SCSI device, but no real block device.
Kevin