Hi Jens,
I'm currently trying to prototype for an IORING_POLL_CANCEL_ON_CLOSE
flag that can be passed to POLL_ADD. With that we'll register
the request in &req->file->f_uring_poll (similar to the file->f_ep list for epoll)
Then we only get a real reference to the file during the call to
vfs_poll() otherwise we drop the fget/fput reference and rely on
an io_uring_poll_release_file() (similar to eventpoll_release_file())
to cancel our registered poll request.
Yes, this is a bit tricky as we hold the file ref across the operation. I'd
be interested in seeing your approach to this, and also how it would
interact with registered files...
It should work fine with fixed files, but I haven't tested it.
But from reading the code I'm wondering what happens in general with pending
requests on a closed fixed file? There's no referencing in io_file_get_fixed(),
or is it done via io_req_set_rsrc_node() together with the
io_rsrc_node_switch_start()/io_queue_rsrc_removal()/io_rsrc_node_switch()
within io_fixed_fd_remove()?
But IORING_POLL_CANCEL_ON_CLOSE doesn't have any effect together with
REQ_F_FIXED_FILE (in my current code). Maybe a io_fixed_fd_remove()
should call __io_async_cancel with IORING_ASYNC_CANCEL_FD_FIXED.
I was also thinking if any pending could be canceled by a close(),
because they all have the registered in the struct file list...
But that might be overkill and io_uring aware applications can just use
IORING_ASYNC_CANCEL_FD_* explicitly. Also fixed files are also only
used by io_uring aware code.
metze
