/dev/null: add IORING_OP_URING_CMD support

This patch adds support for the io_uring command pass through, aka
IORING_OP_URING_CMD, to the /dev/null driver.  As with all of the
/dev/null functionality, the implementation is just a simple sink
where commands go to die, but it should be useful for developers who
need a simple IORING_OP_URING_CMD test device that doesn't require
any special hardware.

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Paul Moore <paul@paul-moore.com>

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 84ca98e..32a932a 100644 (file)
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -480,6 +480,11 @@ static ssize_t splice_write_null(struct pipe_inode_info *pipe, struct file *out,
        return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_null);
 }
 
+static int uring_cmd_null(struct io_uring_cmd *ioucmd, unsigned int issue_flags)
+{
+       return 0;
+}
+
 static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
 {
        size_t written = 0;
@@ -663,6 +668,7 @@ static const struct file_operations null_fops = {
        .read_iter      = read_iter_null,
        .write_iter     = write_iter_null,
        .splice_write   = splice_write_null,
+       .uring_cmd      = uring_cmd_null,
 };
 
 static const struct file_operations __maybe_unused port_fops = {