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

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Date:	Wed, 02 May 2012 15:59:59 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Jan Kara <jack@...e.cz>
CC:	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

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?

> 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.

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.

Paolo

> (if ioctls would be restricted for partitions from the
> beginning, then sure it seems like a cleaner choice). But I don't feel that
> strongly about it.

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