Date: Mon, 7 Nov 2016 12:14:10 +0000 From: Rick Macklem <rmacklem@uoguelph.ca> To: Doug Rabson <dfr@rabson.org> Cc: "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org> Subject: Re: Mount protocol/showmount vs NFSv4 Message-ID: <YTXPR01MB0189A45745319639B9A31CDFDDA70@YTXPR01MB0189.CANPRD01.PROD.OUTLOOK.COM> In-Reply-To: <CACA0VUiZ0v0js42oAkNBADfOyQV0S5BHCXwW2foV_UXG9o1Jkw@mail.gmail.com> References: <YTXPR01MB01893AD86D5F1280DC63CA4BDDA40@YTXPR01MB0189.CANPRD01.PROD.OUTLOOK.COM>, <CACA0VUiZ0v0js42oAkNBADfOyQV0S5BHCXwW2foV_UXG9o1Jkw@mail.gmail.com>
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Doug Rabson wrote:
>
>It seems like a reasonably good idea to disable disable the mount protocol=
if its not >needed. For NFSv4, mountd really doesn't do much other than re=
ad the exports files and >push them into the kernel - does it even need to =
keep running after that for NFSv4?
Probably so that /etc/exports can be reloaded, but that would be the only r=
eason,
assuming "showmount" isn't being supported.
>
>On the subject of showmount, we do have some information on connected clie=
nts which I >suppose you could try to expose but its probably not worth the=
effort.
Some clients (Solaris, I think) don't maintain TCP connections for inactive=
mounts, so
the connections aren't a direct indication of mounts.
Thanks for the comments, rick
On 6 November 2016 at 20:51, Rick Macklem <rmacklem@uoguelph.ca<mailto:rmac=
klem@uoguelph.ca>> wrote:
Hi,
NFSv2 and NFSv3 use a protocol called Mount (implemented by mountd) to try =
and
track mounts/unmounts and report exports to clients. Except for the one RPC=
that
maps a directory path to a File Handle, none of this is needed by NFS. The =
rest is
reported (and never guaranteed to be correct) by showmount(8).
There are a couple of issues related to the Mount protocol.
1 - It uses a dynamically assigned port# via rpcbind (which means hassles f=
or firewalls, etc).
2 - umount(8) currently assumes that it is supported over UDP and fails if =
it is
configured to work over TCP only.
3 - A recent issue was reported where there is a delay for systems configur=
ed for IP6
only related to the handling of localhost. (I'll admit I didn't unders=
tand quite why
there was this 2sec delay, but others familiar with networking confirm=
ed it was
correct behaviour.)
NFSv4 doesn't use the Mount protocol at all and does everything via the NFS=
v4 protocol
serviced at port #2049.
I have never done anything about this, since most were still using NFSv3, b=
ut it seems
that maybe something should be done now?
- What do people think of having a new option on mountd(8) that would be us=
ed for
NFSv4 only servers that disables servicing of Mount RPCs.
--> This would imply that "showmount" would no longer work for it.
--> Note that "showmount" returns nothing useful for NFSv4 mounts,=
since mountd
doesn't know about NFSv4 mounts (and the NFSv4 server doesn'=
t know either,
because there is no concept of a "mount" in the NFSv4 protoc=
ol).
--> It does imply that "showmount -e" will stop working and that in=
fo might be
useful w.r.t. NFSv4 servers.
Umount(8) for NFSv3 is a slightly different problem. It has (for 30years) j=
ust talked to
UDP. If that doesn't work, there is a delay, but the umount still works (an=
d the info
from "showmount" is no longer correct, but it is never guaranteed to be cor=
rect anyhow).
- Should umount(8) use TCP if the NFSv3 mount is using TCP?
--> This could cause it to break for a case where only UDP is supported f=
or the Mount
protocol on the server, but that would be a rare/broken case, I'd g=
uess.
Anyhow, any/all comments on this would be appreciated, rick
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