Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <e1a59fa3eb821e66cdc95fcecc68ef9f9434ddf5.camel@kernel.org>
Subject: Re: [PATCH 1/3] fs/locks: F_UNLCK extension for F_OFD_GETLK
From:   Jeff Layton <jlayton@kernel.org>
To:     stsp <stsp2@yandex.ru>, linux-kernel@vger.kernel.org
Cc:     Chuck Lever <chuck.lever@oracle.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        linux-fsdevel@vger.kernel.org
Date:   Tue, 20 Jun 2023 07:15:38 -0400
In-Reply-To: <e7586b46-ff65-27ff-e829-c6009d7d4808@yandex.ru>
References: <20230620095507.2677463-1-stsp2@yandex.ru>
         <20230620095507.2677463-2-stsp2@yandex.ru>
         <c6d4e620cad72da5f85df03443a64747b5719939.camel@kernel.org>
         <e7586b46-ff65-27ff-e829-c6009d7d4808@yandex.ru>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.48.3 (3.48.3-1.fc38) 
MIME-Version: 1.0
Precedence: bulk

On Tue, 2023-06-20 at 16:00 +0500, stsp wrote:
> Hello,
>=20
> 20.06.2023 15:46, Jeff Layton =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
> > On Tue, 2023-06-20 at 14:55 +0500, Stas Sergeev wrote:
> > > Currently F_UNLCK with F_OFD_GETLK returns -EINVAL.
> > > The proposed extension allows to use it for getting the lock
> > > information from the particular fd.
> > >=20
> > > Signed-off-by: Stas Sergeev <stsp2@yandex.ru>
> > >=20
> > > CC: Jeff Layton <jlayton@kernel.org>
> > > CC: Chuck Lever <chuck.lever@oracle.com>
> > > CC: Alexander Viro <viro@zeniv.linux.org.uk>
> > > CC: Christian Brauner <brauner@kernel.org>
> > > CC: linux-fsdevel@vger.kernel.org
> > > CC: linux-kernel@vger.kernel.org
> > >=20
> > > ---
> > >   fs/locks.c | 23 ++++++++++++++++++++---
> > >   1 file changed, 20 insertions(+), 3 deletions(-)
> > >=20
> > > diff --git a/fs/locks.c b/fs/locks.c
> > > index df8b26a42524..210766007e63 100644
> > > --- a/fs/locks.c
> > > +++ b/fs/locks.c
> > > @@ -868,6 +868,21 @@ static bool posix_locks_conflict(struct file_loc=
k *caller_fl,
> > >   	return locks_conflict(caller_fl, sys_fl);
> > >   }
> > >  =20
> > > +/* Determine if lock sys_fl blocks lock caller_fl. Used on xx_GETLK
> > > + * path so checks for additional GETLK-specific things like F_UNLCK.
> > > + */
> > > +static bool posix_test_locks_conflict(struct file_lock *caller_fl,
> > > +				      struct file_lock *sys_fl)
> > > +{
> > > +	/* F_UNLCK checks any locks on the same fd. */
> > > +	if (caller_fl->fl_type =3D=3D F_UNLCK) {
> > > +		if (!posix_same_owner(caller_fl, sys_fl))
> > > +			return false;
> > > +		return locks_overlap(caller_fl, sys_fl);
> > > +	}
> > > +	return posix_locks_conflict(caller_fl, sys_fl);
> > > +}
> > > +
> > >   /* Determine if lock sys_fl blocks lock caller_fl. FLOCK specific
> > >    * checking before calling the locks_conflict().
> > >    */
> > > @@ -901,7 +916,7 @@ posix_test_lock(struct file *filp, struct file_lo=
ck *fl)
> > >   retry:
> > >   	spin_lock(&ctx->flc_lock);
> > >   	list_for_each_entry(cfl, &ctx->flc_posix, fl_list) {
> > > -		if (!posix_locks_conflict(fl, cfl))
> > > +		if (!posix_test_locks_conflict(fl, cfl))
> > >   			continue;
> > >   		if (cfl->fl_lmops && cfl->fl_lmops->lm_lock_expirable
> > >   			&& (*cfl->fl_lmops->lm_lock_expirable)(cfl)) {
> > > @@ -2207,7 +2222,8 @@ int fcntl_getlk(struct file *filp, unsigned int=
 cmd, struct flock *flock)
> > >   	if (fl =3D=3D NULL)
> > >   		return -ENOMEM;
> > >   	error =3D -EINVAL;
> > > -	if (flock->l_type !=3D F_RDLCK && flock->l_type !=3D F_WRLCK)
> > > +	if (cmd !=3D F_OFD_GETLK && flock->l_type !=3D F_RDLCK
> > > +			&& flock->l_type !=3D F_WRLCK)
> > >   		goto out;
> > >  =20
> > >   	error =3D flock_to_posix_lock(filp, fl, flock);
> > > @@ -2414,7 +2430,8 @@ int fcntl_getlk64(struct file *filp, unsigned i=
nt cmd, struct flock64 *flock)
> > >   		return -ENOMEM;
> > >  =20
> > >   	error =3D -EINVAL;
> > > -	if (flock->l_type !=3D F_RDLCK && flock->l_type !=3D F_WRLCK)
> > > +	if (cmd !=3D F_OFD_GETLK && flock->l_type !=3D F_RDLCK
> > > +			&& flock->l_type !=3D F_WRLCK)
> > >   		goto out;
> > >  =20
> > >   	error =3D flock64_to_posix_lock(filp, fl, flock);
> > This seems like a reasonable sort of interface to add, particularly for
> > the CRIU case.
>=20
> Just for the record: my own cases are
> the remaining 2. CRIU case is not mine
> and I haven't talked to CRIU people
> about that.
>=20
>=20
> >   Using F_UNLCK for this is a bit kludgey, but adding a new
> > constant is probably worse.
> >=20
> > I'm willing to take this in with an eye toward v6.6. Are you also
> > willing to draft up some manpage patches that detail this new interface=
?
> Sure thing.
> As soon as its applied, I'll prepare a man
> patch, or should it be done before that point?

These days, it's a good idea to go ahead and draft that up early. You'll
be surprised what sort of details you notice once you have to start
writing documentation. ;)

You can post it as part of this set on the next posting and just mention
that it's a draft manpage patch. You should also include the linux-api
mailing list on the next posting so we get some feedback on the
interface itself.
--=20
Jeff Layton <jlayton@kernel.org>