linux-kernel - Re: [PATCH] scsi: Silence unnecessary warnings about ioctl to partition

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Date:	Wed, 2 May 2012 21:49:45 +0200
From:	Jan Kara <jack@...e.cz>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Jan Kara <jack@...e.cz>, Jens Axboe <axboe@...nel.dk>,
	LKML <linux-kernel@...r.kernel.org>,
	James Bottomley <JBottomley@...allels.com>,
	linux-scsi@...r.kernel.org
Subject: Re: [PATCH] scsi: Silence unnecessary warnings about ioctl to
 partition

On Wed 02-05-12 15:59:59, Paolo Bonzini wrote:
> Il 02/05/2012 15:51, Jan Kara ha scritto:
> >> > NACK.  I would bet that all the warnings you've seen are for ioctl that
> >> > would have failed anyway with ENOTTY.
> >   Actually, you would loose the bet ;)
> 
> Doh. :)
> 
> > The customer was complaining about
> > warning about SG_IO ioctl. Apparently some Veritas filesystem thread generates
> > a *lot* of these (I don't know if they happen to do all the filesystem IO
> > with SG_IO and I'm not sure I want to know ;).
> 
> Can you at least ask the customer for help finding which command was
> sent?  And perhaps have them try a kernel that blocks SG_IO to see what
> breaks if anything?
  I'm not sure they would be willing to try a different kernel because it's
a production system. But maybe I can find out what SG_IO command is sent
via strace?

> > Also I tend to side with Alan that I don't quite see
> > the point in trying to restrict CAP_SYS_RAWIO threads and thus breaking the
> > compatibility
> 
> For example, we have a customer that wants this:
> 
> * a VM should be able to send vendor-specific commands to a disk via
> SG_IO (vendor-specific commands require CAP_SYS_RAWIO).
> 
> * they want to assign logical volumes or partitions to the same VM
> without letting it read or write outside the logical volume or partition.
  But then it seems like they really want to be able to forbid sending
SG_IO commands to some devices while allowing them for other devices and
the distinction by partition / non-partition is a bit arbitrary?
 
> Of course a better solution for this would be customizable filters for
> SG_IO commands, where a privileged application would open the block
> device with CAP_SYS_RAWIO, set the filter and hand the file descriptor
> to QEMU.  Or alternatively some extension of the device cgroup.  But
> either solution would require a large amount of work.
  I'm not sure whether you need to filter individual SG_IO commands or not.
For your use case it seems that being able to forbid SG_IO completely for
some fd (which would be passed to qemu) would be enough? But maybe filters
are simpler to implement because they already exist, I don't really know...

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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