On Mon, Aug 12, 2019 at 10:36:26AM -0700, Ira Weiny wrote: > On Sat, Aug 10, 2019 at 09:52:31AM +1000, Dave Chinner wrote: > > On Fri, Aug 09, 2019 at 03:58:15PM -0700, ira.weiny@xxxxxxxxx wrote: > > > + /* > > > + * NOTE on F_LAYOUT lease > > > + * > > > + * LAYOUT lease types are taken on files which the user knows that > > > + * they will be pinning in memory for some indeterminate amount of > > > + * time. > > > > Indeed, layout leases have nothing to do with pinning of memory. > > Yep, Fair enough. I'll rework the comment. > > > That's something an application taht uses layout leases might do, > > but it largely irrelevant to the functionality layout leases > > provide. What needs to be done here is explain what the layout lease > > API actually guarantees w.r.t. the physical file layout, not what > > some application is going to do with a lease. e.g. > > > > The layout lease F_RDLCK guarantees that the holder will be > > notified that the physical file layout is about to be > > changed, and that it needs to release any resources it has > > over the range of this lease, drop the lease and then > > request it again to wait for the kernel to finish whatever > > it is doing on that range. > > > > The layout lease F_RDLCK also allows the holder to modify > > the physical layout of the file. If an operation from the > > lease holder occurs that would modify the layout, that lease > > holder does not get notification that a change will occur, > > but it will block until all other F_RDLCK leases have been > > released by their holders before going ahead. > > > > If there is a F_WRLCK lease held on the file, then a F_RDLCK > > holder will fail any operation that may modify the physical > > layout of the file. F_WRLCK provides exclusive physical > > modification access to the holder, guaranteeing nothing else > > will change the layout of the file while it holds the lease. > > > > The F_WRLCK holder can change the physical layout of the > > file if it so desires, this will block while F_RDLCK holders > > are notified and release their leases before the > > modification will take place. > > > > We need to define the semantics we expose to userspace first..... > > Agreed. I believe I have implemented the semantics you describe above. Do I > have your permission to use your verbiage as part of reworking the comment and > commit message? Of course. :) Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
