Re: [Qemu-devel] [PATCH 1/2 v1] blkdrv: Add queue limits parameters for sg block drive

[Paolo Bonzini]

Il 24/08/2012 12:43, Hannes Reinecke ha scritto:
> Hehe. So finally someone else stumbled across this one.
> 
> All is fine and dandy as long as you're able to use scsi-disk.
> As soon as you're forced to use scsi-generic we're in trouble.
> 
> With scsi-generic we actually have two problems:
> 1) scsi-generic just acts as a pass-through and passes the commands
>    as-is, including the scatter-gather information as formatted by
>    the guest. So the guest could easily format an SG_IO comand
>    which will not be compatible with the host.
> 2) The host is not able to differentiate between a malformed
>    SG_IO command and a real I/O error; in both cases it'll return
>    -EIO.
> 
> So we can fix this by either
> a) ignore (as we do nowadays :-)
> b) Fixup scsi-generic to inspect and modify SG_IO information
>    to ensure the host-limits are respected

That's what scsi-block already does.

Perhaps sooner or later we will need a scsi-tape?  That would be fine.

> Yes, it's painful. But in the long run we'll have to do an SG_IO
> inspection anyway, otherwise we'll always be susceptible to malicious
> SG_IO attacks.

I would like to do this in the kernel using BPF.  I posted a possible
spec at
http://www.redhat.com/archives/libvir-list/2012-June/msg00505.html but
the response was, ehm, underwhelming.

Paolo