[OE-core] [OE-Core][PATCH] openssh: Add dependency on ssh for sftp

[Mike Looijmans]

On 02-07-18 23:13, Richard Purdie wrote:
> On Mon, 2018-07-02 at 18:44 +0100, Alex Kiernan wrote:
>> On Mon, Jul 2, 2018 at 4:06 PM Alex Kiernan <alex.kiernan at gmail.com>
>> wrote:
>>>
>>> On Mon, Jul 2, 2018 at 3:55 PM Mike Looijmans <mike.looijmans at topic
>>> .nl> wrote:
>>>>
>>>> The sftp-server runs fine using dropbear as SSH backend, I'd
>>>> expect the same
>>>> to be true for the client. Isn't that the case, and will the sftp
>>>> client only
>>>> work with openssh's ssh?
>>>>
>>>
>>> Interesting question... I hadn't realised dropbear didn't have an
>>> sftp
>>> client, but it's clearly a supported combination:
>>>
>>> https://github.com/mkj/dropbear/blob/1656db9e58e7e8188e4ca27ae4892b
>>> 14949c56a5/dbclient.1#L159
>>>
>>> I'll amend the patch so it depends on ssh not ${PN}-ssh since both
>>> dropbear and openssh provide that.
>>>
>>
>> Hmm... only that gets you this warning:
>>
>> NOTE: Multiple providers are available for runtime ssh (dropbear,
>> openssh)
>> Consider defining a PREFERRED_RPROVIDER entry to match ssh
>>
>> If you've not set it, which feels like a pretty poor upgrade
>> experience; I'm not sure how best to deal with that.
> 
> This is not an easy problem to solve. This is why we have the horrible
> VIRTUAL-RUNTIME_* variables, I wish there were a better way...
> 
> Basically, bitbake has to have some idea which one to build, letting
> the package manager decide at do_rootfs time isn't really good enough
> for deterministic builds.

The dropbear/ssh choice seems to be one that is being postponed until image 
creation time. There's an IMAGE_FEATURE that appears to make the choice:
IMAGE_FEATURES += "ssh-server-dropbear"

Since you're building openssh already, there's no need to instruct bitbake to 
build more at package compile time.

Using RDEPENDS and PREFERRED_RPROVIDER or VIRTUAL-RUNTIME will 'break' a lot 
of existing setups by installing the wrong ssh client without the engineer 
knowing about it. And it will also make it impossible to build two images with 
different choices. I can imaging you'd want to have a small size "recover" 
image with dropbear and a large size "full" image with openssh in the same 
build for the same machine and distro.

M.


Kind regards,

Mike Looijmans
System Expert

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