Re: [Qemu-devel] [PATCH 2/2] ssh: implement private key authentication

[Max Reitz <mreitz@redhat.com>]

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On 29.07.19 13:08, Kevin Wolf wrote:
> Am 26.07.2019 um 16:24 hat Eric Blake geschrieben:
>> On 7/26/19 9:09 AM, Pino Toscano wrote:
>>> Add a 'private-key' option which represents the path of a private key
>>> to use for authentication, and 'private-key-secret' as the name of an
>>> object with its passphrase.
>>>
>>> Signed-off-by: Pino Toscano <ptoscano@redhat.com>
>>
>>> +++ b/qapi/block-core.json
>>> @@ -3226,6 +3226,11 @@
>>>  # @password-secret:     ID of a QCryptoSecret object providing a password
>>>  #                       for authentication (since 4.2)
>>>  #
>>> +# @private-key:         path to the private key (since 4.2)
>>> +#
>>> +# @private-key-secret:  ID of a QCryptoSecret object providing the passphrase
>>> +#                       for 'private-key' (since 4.2)
>>
>> Is password-secret intended to be mutually-exclusive with
>> private-key/private-key-secret?  If so, this should probably utilize an
>> enum for a discriminator
>> { 'enum': 'SshAuth', 'data': ['ssh-agent', 'password', 'private'key'] }
>>
>> then update BlockdevOptionsSsh to be a union type with an optional
>> discriminator (defaulting to ssh-agent) for back-compat, where
>> 'auth':'ssh-agent' needs no further fields, 'auth':'password' adds in a
>> 'secret' field for use as password, or where 'auth':'private-key' adds
>> in both 'key-file' and 'secret' for use as the two pieces needed for
>> private key use.
> 
> Can we actually support optional discriminators when we don't have
> defaults in the QAPI schema yet?

Just chiming in here, because I wanted to throw in that v4 of my “block:
Try to create well-typed json:{} filenames​” series adds that.

>> On a different topic, how much of this work overlaps with the nbdkit ssh
>> plugin? Should we be duplicating efforts with both projects supporting
>> ssh natively, or is it worth considering getting qemu out of the ssh
>> business and instead connecting to an nbd device provided by nbdkit
>> connecting to ssh?
> 
> ssh behaves essentially like a filesystem whereas NBD behaves like a
> block device. This is especially relevant for everything related to the
> file size. As far as I know, using an image format like qcow2 that wants
> to grow the image file isn't possible over NBD, whereas I expect it to
> work with the ssh block driver.

Just using sshfs and file-posix would seem simpler to me, by the way.

Max


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