[PATCH storage v6 0/2] nfs: use rpcinfo as a showmount fallback for nfs3

[Maximiliano Sandoval <m.sandoval@proxmox.com>]

See the respective commit messages.

This came up in enterprise support. In this case the NFS appliance only
supported NFSv3 and the showmount command failed, but rpcbind
succeeded (with -T tcp).

This possibility was discussed with Friedrich and Fiona off-list.

Tested:
 - Created a NFS share on host "B"
 - On host "A" a NFS storage was added (using B's share) with --options vers=3
 - Ran `ss -tulpn4 |grep mountd` on host B to see ports used by showmount
 - The ports listed were blocked on host "A", so that showmount fails:

   /sbin/showmount --no-headers --exports $B
   rpc mount export: RPC: Unable to send; errno = Operation not permitted

 - Ran `pvesm status` on A and checked that the NFS storage is available
 - Created a VM on A with a disk image in the the NFS storage

The later two operations would have failed without the changes here.

Differences from v5:
 - Move note regarding timeout to fallback

Differences from v4:
 - Use proper FIXME: MAJOR VERSION comment
 - Simplify the FIXME comment
 - Move the NFSv4-only note to the fallback branch

Differences from v3:
 - Fix some typos
 - Turn TODO note into FIXME
 - Moved the pitfalls mentioned in the commit message to the FIXME

Differences from v2:
 - add PVE 10 prefix to TODO note
 - rename the rpcinfo helper
 - make the rpcinfo helper private
 - Always run the fallback branch when v4 != 4.
 - Leave nfsv4+rpcinfo comment on call-site

Differences from v1:
 - the name of the helper function was fixed

Maximiliano Sandoval (2):
  nfs: create a helper to get rpcinfo commands
  nfs: use rpcinfo as a showmount fallback for nfs3

 src/PVE/Storage/NFSPlugin.pm | 33 +++++++++++++++++++++++++--------
 1 file changed, 25 insertions(+), 8 deletions(-)

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2.47.3