[Bug 1954716] Re: rpi nfsroot vers=4 not supported anymore?

[Stephen Winnall]

Whilst trying to understand the problem I looked at the source of
nfsmount in klibc. Nfsmount has a switch statement in which it checks
the value of nfsvers and only proceeds if it is 2 or 3. Given that my
version of nfsmount, compiled with klcc, can indeed mount using NFSv4 I
suspect that in libc's version the switch statement only needs to be
extended with the cases 4, 4.0, 4.1 and 4.2. It's not entirely trivial,
but it's hard to understand why it hasn't been done sometime during the
last 15 years.

I may take a closer look when I've fixed my next bug.

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https://bugs.launchpad.net/bugs/1954716

Title:
  rpi nfsroot vers=4 not supported anymore?

Status in klibc package in Ubuntu:
  Confirmed
Status in linux-raspi package in Ubuntu:
  Invalid

Bug description:
  I'm running `5.13.0-1011-raspi #13-Ubuntu SMP PREEMPT Fri Nov 19
  18:40:23 UTC 2021 aarch64 aarch64 aarch64 GNU/Linux` and have
  successfully set up netbooting on my RPi 4B (4GB). When I do not
  specify a `vers=` in cmdline.txt, NFS version 3 is used. I'd like to
  move to version 4, but unlike the setup described in
  https://forums.raspberrypi.com/viewtopic.php?p=1751741#p1751741, I
  cannot get `vers=4` (or any sub-version to work): the console logs
  `invalid value for vers.` for whatever I try.

  Current working cmdline.txt:
  ```
  dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=/dev/nfs nfsroot=192.168.3.101:/srv/pinet/root,tcp ro ip=dhcp rootwait fixrtc splash
  ```

  Nonworking cmdline.txt:
  ```
  dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=/dev/nfs nfsroot=192.168.3.101:/srv/pinet/root,tcp,vers=4 ro ip=dhcp rootwait fixrtc splash
  ```

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