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Re: [Qemu-devel] [PATCH v2] qemu-nbd: only send a limited number of errn

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v2] qemu-nbd: only send a limited number of errno codes on the wire
Date: Fri, 08 May 2015 07:02:57 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 05/08/2015 06:41 AM, Paolo Bonzini wrote:
> On 08/05/2015 14:40, Eric Blake wrote:
>> On 05/08/2015 03:50 AM, Paolo Bonzini wrote:
>>> Right now, NBD includes potentially platform-specific error values in
>>> the wire protocol.

>> Do we also want to handle "case 0: return 0;" on either conversion, or
>> even "case 0: abort();" to ensure that callers are using these helpers
>> correctly?
> Yes, it's much better that way.

Thinking about it a bit more: abort() is fine on the sending side, to
ensure we aren't putting garbage on the wire; but abort() on the
receiving side is a bit risky (we should be handling a corrupted
incoming stream gracefully - a malicious sender should not be able to
crash us).  Of course, once we've detected a corrupted incoming stream,
we can't do much for the block device the stream was supposed to
represent (perhaps treat it as EIO and declare the device dead), but
that's still better than aborting.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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