Re: [PATCH v2] btrfs: add io_uring interface for encoded writes

[David Sterba <dsterba@suse.cz>]

On Fri, Jan 10, 2025 at 05:23:52PM +0000, Mark Harmstone wrote:
> Add an io_uring interface for encoded writes, with the same parameters
> as the BTRFS_IOC_ENCODED_WRITE ioctl.
> 
> As with the encoded reads code, there's a test program for this at
> https://github.com/maharmstone/io_uring-encoded, and I'll get this
> worked into an fstest.
> 
> How io_uring works is that it initially calls btrfs_uring_cmd with the
> IO_URING_F_NONBLOCK flag set, and if we return -EAGAIN it tries again in
> a kthread with the flag cleared.
> 
> Ideally we'd honour this and call try_lock etc., but there's still a lot
> of work to be done to create non-blocking versions of all the functions
> in our write path. Instead, just validate the input in
> btrfs_uring_encoded_write() on the first pass and return -EAGAIN, with a
> view to properly optimizing the happy path later on.
> 
> Signed-off-by: Mark Harmstone <maharmstone@fb.com>
> ---
> Changelog:
> * Version 2: switched to using io_uring_cmd_get_async_data, so that we
> only copy from userspace once

I've added this to for-next now, it hasn't been in linux-next so far but
we have at least one week before the merge window. The io_uring+read is
about to be released and there's no reason to delay the write for one
whole dev cycle. Any fixups please send as separate patches. Thanks.