Re: [PATCH v4 0/5] btrfs: io_uring interface for encoded reads

[David Sterba <dsterba@suse.cz>]

On Tue, Oct 22, 2024 at 03:50:15PM +0100, Mark Harmstone wrote:
> This is version 4 of a patch series to add an io_uring interface for
> encoded reads. The principal use case for this is to eventually allow
> btrfs send and receive to operate asynchronously, the lack of io_uring
> encoded I/O being one of the main blockers for this.
> 
> I've written a test program for this, which demonstrates the ioctl and
> io_uring interface produce identical results: https://github.com/maharmstone/io_uring-encoded

We'll need a test utility for fstests too.

> Changelog:
> v4:
> * Rewritten to avoid taking function pointer
> * Removed nowait parameter, as this could be derived from iocb flags
> * Fixed structure not getting properly initialized
> * Followed ioctl by capping uncompressed reads at EOF
> * Rebased against btrfs/for-next
> * Formatting fixes
> * Rearranged structs to minimize holes
> * Published test program
> * Fixed potential data race with userspace
> * Changed to use io_uring_cmd_to_pdu helper function
> * Added comments for potentially confusing parts of the code

There are some more style issues and changelog updates but overall looks
ok to me. We're now in rc5 so we need to add it to for-next now or
postpone for next cycle (but I don't see a reason why).

I've noticed CONFIG_IO_URING is a config option, do we need some ifdef
protection or are the definitions provided unconditionally. We may also
need to ifdef out the ioctl code if io_uring is not built in.