On Thu, Mar 7, 2019 at 1:04 PM Stefan Metzmacher <metze@xxxxxxxxx> wrote: > > 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. Getting back to this. Thanks all for the valuable inputs. Next week is LSF/MM and I was assigned a 30 minute slot on filesystems track to discuss "NFS/SMB file share". So let me try to echo what I read on this thread and how I understand what APIs samba needs from the kernel. > > If we want to design an useful API, we also need to think about > all features: > - file oplock/leases Kernel can have a flavor of leases which are not broken by opens from threads of the process holding the lease. Bruce has some patches along those lines for knfsd and SMB R/RW leases could use this flavor if it was exported to userspace? For SMB RH/RWH leases and Ganesha delegations, server could keep track of its own handles/clients and break leases within the same process without involving the kernel. Am I wrong? > - directory leases I have WIP on fsnotify directory pre modification hooks. There is opposition from fsnotify maintainer to add new userspace APIs that can create kernel->user->kernel deadlocks, like the deadlocks currently reported with fanotify permission events. Need to see if we can find a middle ground between "post modification notifications" and "pre modification permission" API, somewhere along the lines of regular file lease breaking API. > - share modes Volker told me he thinks samba can enforce share modes by a single daemon policing all opens in the system with fanotify. I think he is right. If anyone thinks differently please speak up. > - 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 So this interface exists in the kernel. Nothing more required from the kernel API. Right? > - 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. I should hope that the new AIO API (http://kernel.dk/io_uring.pdf) would solve those problems as well as other issues that samba has w.r.t dispatching AIO. > > 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. > Tested interfaces - good idea ;-) If anyone has any comments about my view of required new interfaces, or important things that I missed, please say so before Tuesday! Thanks, Amir.
