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    SubjectRe: [PATCH RFC 02/24] filelock: add a lm_set_conflict lease_manager callback
    On Fri, Mar 15, 2024 at 12:52:53PM -0400, Jeff Layton wrote:
    > The NFSv4.1 protocol adds support for directory delegations, but it
    > specifies that if you already have a delegation and try to request a new
    > one on the same filehandle, the server must reply that the delegation is
    > unavailable.
    >
    > Add a new lease_manager callback to allow the lease manager (nfsd in
    > this case) to impose extra checks when performing a setlease.
    >
    > Signed-off-by: Jeff Layton <jlayton@kernel.org>
    > ---
    > fs/locks.c | 5 +++++
    > include/linux/filelock.h | 10 ++++++++++
    > 2 files changed, 15 insertions(+)
    >
    > diff --git a/fs/locks.c b/fs/locks.c
    > index cb4b35d26162..415cca8e9565 100644
    > --- a/fs/locks.c
    > +++ b/fs/locks.c
    > @@ -1822,6 +1822,11 @@ generic_add_lease(struct file *filp, int arg, struct file_lease **flp, void **pr
    > continue;
    > }
    >
    > + /* Allow the lease manager to veto the setlease */
    > + if (lease->fl_lmops->lm_set_conflict &&
    > + lease->fl_lmops->lm_set_conflict(lease, fl))
    > + goto out;
    > +
    > /*
    > * No exclusive leases if someone else has a lease on
    > * this file:
    > diff --git a/include/linux/filelock.h b/include/linux/filelock.h
    > index daee999d05f3..c5fc768087df 100644
    > --- a/include/linux/filelock.h
    > +++ b/include/linux/filelock.h
    > @@ -49,6 +49,16 @@ struct lease_manager_operations {
    > int (*lm_change)(struct file_lease *, int, struct list_head *);
    > void (*lm_setup)(struct file_lease *, void **);
    > bool (*lm_breaker_owns_lease)(struct file_lease *);
    > +
    > + /**
    > + * lm_set_conflict - extra conditions for setlease
    > + * @new: new file_lease being set
    > + * @old: old (extant) file_lease
    > + *
    > + * This allows the lease manager to add extra conditions when
    > + * setting a lease.

    To make it clear which return value causes add_lease() to abort, I'd
    rather see API contract-style descriptions of the meaning of the
    return values instead of this design note. Something like:

    * Return values:
    * %true: @new and @old conflict
    * %false: No conflict detected


    > + */
    > + bool (*lm_set_conflict)(struct file_lease *new, struct file_lease *old);
    > };
    >
    > struct lock_manager {
    >
    > --
    > 2.44.0
    >

    --
    Chuck Lever

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