https://github.com/torvalds/linux/blob/0b5547c51827e053cc754db47d3ec3e6c2c45... 9p has different behavior if you request `O_NONBLOCK` - the blocking behavior just calls the nonblocking function in a loop. This behaviour was explicitly added in https://lore.kernel.org/all/20200205003457.24340-2-l29ah@cock.li/T/#u with the stated reasoning being:
I want to interface with synthetic file systems that represent arbitrary data streams. The one where i've hit the problem is reading the log of a XMPP chat client that blocks if there's no new data available.
Given this, I don't think it's likely reverting this will be accepted. If this is a WONTFIX from the position of the wine project, where is best for me to document that 9p is an unsupported filesystem to run wine from?