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Date: Thu, 15 Aug 2019 07:56:30 +1000 From: Dave Chinner <david@...morbit.com> To: Jeff Layton <jlayton@...nel.org> Cc: ira.weiny@...el.com, Andrew Morton <akpm@...ux-foundation.org>, Jason Gunthorpe <jgg@...pe.ca>, Dan Williams <dan.j.williams@...el.com>, Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>, Theodore Ts'o <tytso@....edu>, John Hubbard <jhubbard@...dia.com>, Michal Hocko <mhocko@...e.com>, linux-xfs@...r.kernel.org, linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-nvdimm@...ts.01.org, linux-ext4@...r.kernel.org, linux-mm@...ck.org Subject: Re: [RFC PATCH v2 02/19] fs/locks: Add Exclusive flag to user Layout lease On Wed, Aug 14, 2019 at 10:15:06AM -0400, Jeff Layton wrote: > On Fri, 2019-08-09 at 15:58 -0700, ira.weiny@...el.com wrote: > > From: Ira Weiny <ira.weiny@...el.com> > > > > Add an exclusive lease flag which indicates that the layout mechanism > > can not be broken. > > > > Exclusive layout leases allow the file system to know that pages may be > > GUP pined and that attempts to change the layout, ie truncate, should be > > failed. > > > > A process which attempts to break it's own exclusive lease gets an > > EDEADLOCK return to help determine that this is likely a programming bug > > vs someone else holding a resource. ..... > > diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h > > index baddd54f3031..88b175ceccbc 100644 > > --- a/include/uapi/asm-generic/fcntl.h > > +++ b/include/uapi/asm-generic/fcntl.h > > @@ -176,6 +176,8 @@ struct f_owner_ex { > > > > #define F_LAYOUT 16 /* layout lease to allow longterm pins such as > > RDMA */ > > +#define F_EXCLUSIVE 32 /* layout lease is exclusive */ > > + /* FIXME or shoudl this be F_EXLCK??? */ > > > > /* operations for bsd flock(), also used by the kernel implementation */ > > #define LOCK_SH 1 /* shared lock */ > > This interface just seems weird to me. The existing F_*LCK values aren't > really set up to be flags, but are enumerated values (even if there are > some gaps on some arches). For instance, on parisc and sparc: I don't think we need to worry about this - the F_WRLCK version of the layout lease should have these exclusive access semantics (i.e other ops fail rather than block waiting for lease recall) and hence the API shouldn't need a new flag to specify them. i.e. the primary difference between F_RDLCK and F_WRLCK layout leases is that the F_RDLCK is a shared, co-operative lease model where only delays in operations will be seen, while F_WRLCK is a "guarantee exclusive access and I don't care what it breaks" model... :) Cheers, Dave. -- Dave Chinner david@...morbit.com
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