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Message-ID: <06427133d603e3ff521bcd1c3d0d3ba777848606.camel@kernel.org>
Subject: Re: [PATCH v4 0/3] convert write_threads, write_version and
 write_ports to netlink commands
From: Jeff Layton <jlayton@kernel.org>
To: NeilBrown <neilb@suse.de>
Cc: Lorenzo Bianconi <lorenzo@kernel.org>, linux-nfs@vger.kernel.org, 
 lorenzo.bianconi@redhat.com, chuck.lever@oracle.com,
 netdev@vger.kernel.org,  kuba@kernel.org
Date: Mon, 27 Nov 2023 07:35:34 -0500
In-Reply-To: <169982054606.2582.2797096885323571291@noble.neil.brown.name>
References: <cover.1699095665.git.lorenzo@kernel.org>
	, <7fdd6dd0d8ab75181eb350f78a4822a039cacaa5.camel@kernel.org>
	, <ZVCiyNQtkumDheU4@lore-desk>
	, <0f0467f396777722022403727824104b4f0a8d85.camel@kernel.org>
	 <169982054606.2582.2797096885323571291@noble.neil.brown.name>
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On Mon, 2023-11-13 at 07:22 +1100, NeilBrown wrote:
> On Sun, 12 Nov 2023, Jeff Layton wrote:
> > On Sun, 2023-11-12 at 11:02 +0100, Lorenzo Bianconi wrote:
> > > > On Sat, 2023-11-04 at 12:13 +0100, Lorenzo Bianconi wrote:
> > > > > Introduce write_threads, write_version and write_ports netlink
> > > > > commands similar to the ones available through the procfs.
> > > > >=20
> > > > > Changes since v3:
> > > > > - drop write_maxconn and write_maxblksize for the moment
> > > > > - add write_version and write_ports commands
> > > > > Changes since v2:
> > > > > - use u32 to store nthreads in nfsd_nl_threads_set_doit
> > > > > - rename server-attr in control-plane in nfsd.yaml specs
> > > > > Changes since v1:
> > > > > - remove write_v4_end_grace command
> > > > > - add write_maxblksize and write_maxconn netlink commands
> > > > >=20
> > > > > This patch can be tested with user-space tool reported below:
> > > > > https://github.com/LorenzoBianconi/nfsd-netlink.git
> > > > > This series is based on the commit below available in net-next tr=
ee
> > > > >=20
> > > > > commit e0fadcffdd172d3a762cb3d0e2e185b8198532d9
> > > > > Author: Jakub Kicinski <kuba@kernel.org>
> > > > > Date:   Fri Oct 6 06:50:32 2023 -0700
> > > > >=20
> > > > > =A0=A0=A0=A0tools: ynl-gen: handle do ops with no input attrs
> > > > >=20
> > > > > =A0=A0=A0=A0The code supports dumps with no input attributes curr=
ently
> > > > > =A0=A0=A0=A0thru a combination of special-casing and luck.
> > > > > =A0=A0=A0=A0Clean up the handling of ops with no inputs. Create e=
mpty
> > > > > =A0=A0=A0=A0Structs, and skip printing of empty types.
> > > > > =A0=A0=A0=A0This makes dos with no inputs work.
> > > > >=20
> > > > > Lorenzo Bianconi (3):
> > > > > =A0=A0NFSD: convert write_threads to netlink commands
> > > > > =A0=A0NFSD: convert write_version to netlink commands
> > > > > =A0=A0NFSD: convert write_ports to netlink commands
> > > > >=20
> > > > > =A0Documentation/netlink/specs/nfsd.yaml |  83 ++++++++
> > > > > =A0fs/nfsd/netlink.c                     |  54 ++++++
> > > > > =A0fs/nfsd/netlink.h                     |   8 +
> > > > > =A0fs/nfsd/nfsctl.c                      | 267 ++++++++++++++++++=
+++++++-
> > > > > =A0include/uapi/linux/nfsd_netlink.h     |  30 +++
> > > > > =A0tools/net/ynl/generated/nfsd-user.c   | 254 ++++++++++++++++++=
++++++
> > > > > =A0tools/net/ynl/generated/nfsd-user.h   | 156 +++++++++++++++
> > > > > =A07 files changed, 845 insertions(+), 7 deletions(-)
> > > > >=20
> > > >=20
> > > > Nice work, Lorenzo! Now comes the bikeshedding...
> > >=20
> > > Hi Jeff,
> > >=20
> > > >=20
> > > > With the nfsdfs interface, we sort of had to split things up into
> > > > multiple files like this, but it has some drawbacks, in particular =
with
> > > > weird behavior when people do things out of order.
> > >=20
> > > what do you mean with 'weird behavior'? Something not expected?
> > >=20
> >=20
> > Yeah.
> >=20
> > For instance, if you set up sockets but never write anything to the
> > "threads" file, those sockets will sit around in perpetuity. Granted
> > most people use rpc.nfsd to start the server, so this generally doesn't
> > happen often, but it's always been a klunky interface regardless.
>=20
> If you set up sockets but *do* write something to the "threads" file,
> then those sockets will *still* sit around in perpetuity.
> i.e. until you shut down the NFS server (rpc.nfsd 0).
>=20
> I don't really see the problem.
>=20
> It is true that you can use use the interface to ask for meaningless
> things.  The maxim that applies is "If you make it fool-proof, only a
> fool will use it". :-)
>=20
> I'm not against exploring changes to the interface style in conjunction
> with moving from nfsd-fs to netlink, but I would want a bit more
> justification for any change.
>=20
>=20

Mostly my justification is that that occasionally we do add new settings
for nfsd, and having a single extensible command may make that simpler
to deal with.

> >=20
> > > >=20
> > > > Would it make more sense to instead have a single netlink command t=
hat
> > > > sets up ports and versions, and then spawns the requisite amount of
> > > > threads, all in one fell swoop?
> > >=20
> > > I do not have a strong opinion about it but I would say having a dedi=
cated
> > > set/get for each paramater allow us to have more granularity (e.g. if=
 you want
> > > to change just a parameter we do not need to send all of them to the =
kernel).
> > > What do you think?
> > >=20
> >=20
> > It's pretty rare to need to twiddle settings on the server while it's u=
p
> > and running. Restarting the server in the face of even minor changes is
> > not generally a huge problem, so I don't see this as necessary.
>=20
> Restarting the server is not zero-cost.  It restarts the grace period.
> So I would rather not require it for minor changes.
>=20
>=20

That is a good point. That said, we wouldn't necessarily need to require
restarting the server on a reconfigure. Some settings could be changed
without a server restart.

In any case, I'll withdraw my objection and we can do this with multiple
commands for now. We can always add a single command later, and just fix
up rpc.nfsd to hide all of the details of the different interfaces at
that time if we think it's helpful.

Cheers,
--
Jeff Layton <jlayton@kernel.org>