Subject: Re: [Spice-devel] [RFC PATCH 1/1] Add a usbredir kernel module to
 remotely connect USB devices over IP.
To: Oliver Neukum <oneukum@suse.com>,
        "Daniel P. Berrange" <berrange@redhat.com>
References: <1435700650-640-1-git-send-email-jwhite@codeweavers.com>
 <1435700650-640-2-git-send-email-jwhite@codeweavers.com>
 <20150701090619.GB16822@redhat.com> <1435826719.13145.10.camel@suse.com>
Cc: Jeremy White <jwhite@codeweavers.com>, spice-devel@lists.freedesktop.org,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
From: Hans de Goede <hdegoede@redhat.com>
Message-ID: <559521E5.2090400@redhat.com>
Date: Thu, 2 Jul 2015 13:35:01 +0200
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Hi,

On 02-07-15 10:45, Oliver Neukum wrote:
> On Wed, 2015-07-01 at 10:06 +0100, Daniel P. Berrange wrote:
>
>> I don't really think it is sensible to be defining & implementing new
>> network services which can't support strong encryption and authentication.
>> Rather than passing the file descriptor to the kernel and having it do
>> the I/O directly, I think it would be better to dissassociate the kernel
>> from the network transport, and thus leave all sockets layer data I/O
>> to userspace daemons so they can layer in TLS or SASL or whatever else
>> is appropriate for the security need.
>
> Hi,
>
> this hits a fundamental limit. Block IO must be done entirely in kernel
> space or the system will deadlock. The USB stack is part of the block
> layer and the SCSI error handling. Thus if you involve user space you
> cannot honor memory allocation with GFP_NOFS and you break all APIs
> where we pass GFP_NOIO in the USB stack.
>
> Supposed you need to reset a storage device for error handling.
> Your user space programm does a syscall, which allocates memory
> and needs to launder pages. It proceeds to write to the storage device
> you wish to reset.
>
> It is the same problem FUSE has with writable mmap. You cannot do
> block devices in user space sanely.

So how is this dealt with for usbip ?

Regards,

Hans
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