Re: [Qemu-devel] [PATCH 1/3] curl: Fix parsing of readahead option from filename

[Eric Blake <eblake@redhat.com>]

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On 05/01/2014 02:56 AM, Matthew Booth wrote:
> On 30/04/14 16:16, Kevin Wolf wrote:
>> Am 30.04.2014 um 16:20 hat Matthew Booth geschrieben:
>>> curl_parse_filename wasn't removing the option string from the url,
>>> resulting in a 404.
>>>


> 
> Alternatively I could completely change the syntax. However, the only
> 'safe' syntax I can think of would involve ugly custom escaping, which
> would probably catch out more people than unsafe option parsing. I'm
> open to suggestions.

The name is a URI, so it should already be possible to use URI escaping
(percent-hex-hex) for any character that must be interpreted as part of
the filename rather than as a bogus query.  Therefore, you should be
strict and require that the user passes in a valid URI with all options
known and with the filename spelled correctly using URI escapes, rather
than loose and parsing what would otherwise be garbage as a possible
weird filename.

> 
> On a related note, do you know if it's possible to specify a backing
> file with separated options? i.e.:
> 
> qemu-img create -f qcow2 -o
> backingfile.url='http://example.com/path',backingfile.readahead='64k'
> /tmp/foo.qcow2

It should be possible; in fact, if the backing file is supported in
BlockdevOptions for the QMP blockdev-add command it already is.  If it
is not supported in BlockdevOptions, then we need structured options
added to make it possible.  But you can use any of the backing stores
that are already structured as your example.

> 
> I suspect that qcow2 only stores a string, so probably not, but I
> thought I'd ask.

There's a proposal for a new json: protocol, which allows storing ANY
arbitrary BlockdevOptions as a flat string in the qcow2 metadata (within
the limits of the header format which forces you to 1024 bytes or less).

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


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