Before this change all exports were exported as root and the --uid and
--gid flags of the VFS were ignored.
This fixes the issue by exporting the UID and GID correctly which
default to the current user and group unless set explicitly.
Before this change, writing files to an `nfsmount` via Finder on macOS would
cause critical errors, rendering `nfsmount` effectively unusable on macOS. This
change fixes the issue so that writes via Finder should be possible.
The issue was primarily caused by the handler's HandleLimit being set to -1. -1 is
the correct default for a NullAuthHandler, but not for a CachingHandler, which
interprets -1 not as "no limit" but as "no cache".
This change sets a high default of 1000000, and gives the user control over it
with a new --nfs-cache-handle-limit flag (available in both `serve nfs` and
`nfsmount`. A minimum of 5 is enforced, as any lower than this will be
insufficient to support directory listing.
Summary:
Adding a new command to serve any remote over NFS. This is only useful for new macOS versions where FUSE mounts are not available.
* Added willscot/go-nfs dependency and updated go.mod and go.sum
Test Plan:
```
go run rclone.go serve nfs --http-url https://beta.rclone.org :http:
```
Test that it is serving correctly by mounting the NFS directory.
```
mkdir nfs-test
mount -oport=58654,mountport=58654 localhost: nfs-test
```
Then we can list the mounted directory to see it is working.
```
ls nfs-test
```
