Re: Better interop for NFS/SMB file share mode/reservation

Stefan Metzmacher
2019-03-07T11:04:10Z

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Am 06.03.19 um 22:25 schrieb Ralph Böhme via samba-technical:
>
> Jeremy Allison wrote:
>> On Wed, Mar 06, 2019 at 03:31:08PM -0500, Jeff Layton wrote:
>>> On Wed, 2019-03-06 at 10:11 -0500, J. Bruce Fields wrote:
>>>>
>>>> Jeff, wasn't there some work (on Ceph maybe?) on a userspace delegation
>>>> API? Is that close to what's needed?
>>>>
>>>
>>> Here's the C headers for that stuff:
>>>
>>> https://github.com/ceph/ceph/blob/7ba6bece4187eda5d05a9b84211fe6ba8dd287bd/src/include/cephfs/libcephfs.h#L1734
>>>
>>> It's simple enough and works for us in ganesha, and I think we can
>>> probably adapt it to samba without too much difficulty. The callback
>>> doesn't seem like it'll do for a kernel API though -- you'd almost
>>> certainly need to do something different there (signals? inotify?).
>>
>> SMB3 leases have R/RW and Handle-based leases.
>
> Just to be precise: SMB2.1+ has R, RH, RW and RWH leases.
>
>> Handle leases allow multiple opens of the same pathname
>> that get different handles to share the lease, allowing
>> a client redirector to delay opens or closes locally
>> so long as it has a handle lease.
>
> That'a a propertly of leases in general, not just H-leases. The client provides a lease key which is a GUID with each lease request
>
>>
>> Here are the semantics:
>>
>> https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-smb2/d8df943d-6ad7-4b30-9f58-96ae90fc6204
>>
>> I'm not sure a simple file-descriptor based API is
>> enough for us. Can he have a uuid or token based
>> API instead where the server can chose what fd's
>> to cover with a token ?
>
> Yes, that would be ideal.

If we want to design an useful API, we also need to think about
all features:
- file oplock/leases
- directory leases
- share modes
- disconnected handles (for durable and persistent handles),
which exists within the kernel for a while and can be reattached
to process, using some kind of cookie and the same euid
- the API needs ways to use epoll in order to do async opens
and lease breaks. For opens the model of async socket connects
could be used. Leases could have a signalfd-style api.

We may not need everything at once, but we should have the full picture
in mind. And we need working code in kernel and userspace that passes
all tests (we may need to add additional test). Otherwise the kernel
creates new syscalls, which wouldn't be used by Samba in the end.

metze

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