`cargo test` is always failing on FreeBSD, the following is one of the
errors:
```
---- tests::test_simple_overflow_page stdout ----
thread 'tests::test_simple_overflow_page' panicked at test/src/lib.rs:32:84:
called `Result::unwrap()` on an `Err` value: IOError(Os { code: 2, kind: NotFound, message: "No such file or directory" })
```
After some digging, I found that the `open_file` function in
`core/io/generic.rs` does not respect the `OpenFlags::Create` flag. This
commit adds support for file creation in the `open_file` function.
`cargo test` now passes on FreeBSD.
Adds a struct WrappedIOUring which contains a IoUring and a pending_ops
field. Entry submission and popping from the queue is done through
functions operating on it, which also maintains pending_ops count
NOTE: This is a bit weird/hacky since in get_completion we create a
CompletionQueue and just call its next(). If it were a normal iterator
it would always return the same first item. However it is a queue posing
as an iterator which makes this work.
Add a `pending_ops` field to `InnerLinuxIO` struct which is incremented
for each operation submitted to the ring and decremented when they are
taken off the completion queue. With this, we can exit from run_once if
there are no pending operations. Otherwise, in that case, it would hang
indefinitely due to call of `ring.submit_and_wait(1)`
...but keep going if the filesystem does not support it. Fixes Limbo on
older Linux kernels that have io_uring but don't support direct I/O on
all filesystems, such as tmpfs or encryptfs.
