I'm writing three filesystems for my applications needs. For the first the whole tflush, tversion (which is far more dangerous than tflush for a backend server) isn't important because this is a read-only bootfilesystem which replaces the boot infrastructure (9fat, nvram, kfs/fossil/paqfs/...) with a single partition (without the need to search for plan9.ini, boot, the kernel aso).

The second filesystem is my fileserver/database front-end which resides on a host in the internet. And 9p is poison for this task (as defined in man 5 section). The current 9p protocol resembles in my opinion some kind of a transaction system while lacking the most important message "commit". Tversion starts a transaction (called session in the manual) and Tflush and Tversion are aquivalents to a "rollback" while there is no way to "commit" changes to the server. If the client loses his connection a real world backend would have to rollback all changes. Also Tflush, Tversion would make it necessary to store all changes temporarily while there the only message that represents a semi-commit would be Tclunk.

The fileservers used on plan9 aren't affected by the lack of a session commit cause kfs as well as fossil are journaling filesystems (at least operatable in this way) but 9p enpowers the client while endangering the server.

I rewrote fcall, lib9p to understand the 9p protocol and decided to write a front-end for my hosted fileserver(database+filesystem) based on a tcp protocol. While a plan9 client establishes a connection with sending Tversion I send a "begin" to the main server. After each Tclunk I send "commit" and "begin" and after a Tflush or Tversion I send a "rollback" and a "begin" to the Server for Tflush an immediate Rflush to the client. I'm not happy with this cause Tclunk as the marker for "commit" and "begin" isn't right but thats the way I did it now.

While at it I would also reduce the amount of information a client can aquire by a tstat or write with a twstat. I would also make ntags 64 bit or at least 32 bit.

To summarize : I think the lack of a "commit" while starting a session with Tversion rolling it back with Tflush or Tversion has caused me some headache.