[RFC nfs-utils PATCH 0/2] add systemd generator for the rpc_pipefs mountpoint

[Scott Mayhew <smayhew@redhat.com>]

These patches aim to make it a little easier to change the mountpoint.
Right now if you change the pipefs-directory in /etc/nfs.conf, you still
need to manually override the dependencies in the systemd unit files in
order for the change to actually work.  

The first patch moves rpc.idmapd's (mostly) undocumented
pipefs-directory from /etc/idmapd.conf to /etc/nfs.conf, which rpc.gssd
already can use for it's pipefs-directory configuration.

The second patch adds a systemd generator that reads the
pipefs-directory configurations from /etc/nfs.conf, and if they differ
from the default it will automatically 1) create a systemd mount unit
file for the pipefs mountpoint and 2) it will create a drop-in
configuration file to override the Requires= and After= directives for
that service.

I did run into a bit of a snag though.  Depsite overriding the
dependencies for both idmapd and gssd, I wind up with two pipefs
filesystems mounted:

[root@coeurl ~]# grep pipefs /proc/mounts
sunrpc /var/lib/nfs/rpc_pipefs rpc_pipefs rw,relatime 0 0
sunrpc /run/rpc_pipefs rpc_pipefs rw,relatime 0 0

systemd still shows the dependency on the default pipefs mountpoint:

[root@coeurl ~]# systemctl list-dependencies --before var-lib-nfs-rpc_pipefs.mount
var-lib-nfs-rpc_pipefs.mount
● ├─nfs-idmapd.service
● └─rpc-gssd.service

as well as the new one:

[root@coeurl ~]# systemctl list-dependencies --before run-rpc_pipefs.mount
run-rpc_pipefs.mount
● ├─nfs-idmapd.service
● └─rpc-gssd.service

The drop-in configs to override the pipefs mountpoint look correct.  I'm
clearing both Requires= and After= before setting them:

[root@coeurl ~]# cat /run/systemd/generator/nfs-idmapd.service.d/10-pipefs.conf 
# Automatically generated by rpc-pipefs-generator

[Unit]
Requires=
Requires=run-rpc_pipefs.mount
After=
After=run-rpc_pipefs.mount local-fs.target

[root@coeurl ~]# cat /run/systemd/generator/rpc-gssd.service.d/10-pipefs.conf 
# Automatically generated by rpc-pipefs-generator

[Unit]
Requires=
Requires=run-rpc_pipefs.mount
After=
After=run-rpc_pipefs.mount

The generated mount unit file also looks correct:

[root@coeurl ~]# cat /run/systemd/generator/run-rpc_pipefs.mount 
# Automatically generated by rpc-pipefs-generator

[Unit]
Description=RPC Pipe File System
DefaultDependencies=no
After=systemd-tmpfiles-setup.service
Conflicts=umount.target

[Mount]
What=sunrpc
Where=/run/rpc_pipefs
Type=rpc_pipefs

systemd shows that the drop-in config was picked up:

[root@coeurl ~]# systemctl status nfs-idmapd
● nfs-idmapd.service - NFSv4 ID-name mapping service
   Loaded: loaded (/usr/lib/systemd/system/nfs-idmapd.service; static; vendor preset: disabled)
  Drop-In: /run/systemd/generator/nfs-idmapd.service.d
           └─10-pipefs.conf
   Active: active (running) since Fri 2017-03-31 16:54:24 EDT; 5min ago
  Process: 27831 ExecStart=/usr/sbin/rpc.idmapd $RPCIDMAPDARGS (code=exited, status=0/SUCCESS)
 Main PID: 27832 (rpc.idmapd)
    Tasks: 1 (limit: 4915)
   CGroup: /system.slice/nfs-idmapd.service
           └─27832 /usr/sbin/rpc.idmapd

and lsof shows that the correct mountpoint is being used:

[root@coeurl ~]# lsof -p 27832 2>/dev/null | grep pipefs
rpc.idmap 27832 root   10r      DIR               0,42        0        103 /run/rpc_pipefs/nfs

The same for gssd:

[root@coeurl ~]# systemctl status rpc-gssd
● rpc-gssd.service - RPC security service for NFS client and server
   Loaded: loaded (/usr/lib/systemd/system/rpc-gssd.service; static; vendor preset: disabled)
  Drop-In: /run/systemd/generator/rpc-gssd.service.d
           └─10-pipefs.conf
   Active: active (running) since Fri 2017-03-31 16:54:29 EDT; 6min ago
  Process: 27839 ExecStart=/usr/sbin/rpc.gssd $RPCGSSDARGS (code=exited, status=0/SUCCESS)
 Main PID: 27840 (rpc.gssd)
    Tasks: 1 (limit: 4915)
   CGroup: /system.slice/rpc-gssd.service
           └─27840 /usr/sbin/rpc.gssd

[root@coeurl ~]# lsof -p 27840 2>/dev/null | grep pipefs
rpc.gssd 27840 root  cwd       DIR               0,42        0   24637 /run/rpc_pipefs
rpc.gssd 27840 root    7r      DIR               0,42        0   24637 /run/rpc_pipefs
rpc.gssd 27840 root   11u     FIFO               0,42      0t0     112 /run/rpc_pipefs/gssd/clntXX/gssd

So it looks like systemd is using both sets of dependencies, even though
the programs themselves are only looking for what's specified in
/etc/nfs.conf.  I'm not sure what to do about that.  Maybe remove the
var-lib-nfs-rpc_pipefs.mount unit as well as the dependencies in the
nfs-idmapd.service and rpc-gssd.service files, and have the generator
create those automatically as well?

-Scott

Scott Mayhew (2):
  idmapd: move the pipefs-directory config option to nfs.conf
  systemd: add a generator for the rpc_pipefs mountpoint

 .gitignore                     |   1 +
 nfs.conf                       |   3 +
 systemd/Makefile.am            |   4 +-
 systemd/nfs.conf.man           |   9 ++
 systemd/rpc-pipefs-generator.c | 256 +++++++++++++++++++++++++++++++++++++++++
 systemd/rpc-svcgssd.service    |   3 +-
 utils/idmapd/idmapd.c          |  35 +++---
 utils/idmapd/idmapd.man        |  19 ++-
 8 files changed, 305 insertions(+), 25 deletions(-)
 create mode 100644 systemd/rpc-pipefs-generator.c

-- 
2.9.3