This patch uses heuristics that seem dangerous to me:

> The 9P filesystem protocol relies on stateful file opens which map protocol-level FIDs to host file descriptors. The FreeBSD vnode interface doesn't really support this and we use heuristics to guess the right FID to use for file operations. This can be confused by privilege lowering and does not guarantee that the FID created for a given file open is always used for file operations, even if the calling process is using the file descriptor from the original open call. Improving this would involve changes to the vnode interface which is out-of-scope for this import.

Where would you use something with such unreliable heuristics??