[PATCH 6/8] block: add example ioctl

[Jens Axboe <axboe@xxxxxxxxx>]

Grab op == 1, BLOCK_URING_OP_IOCTL, and use it to implement basic
ioctl functionality.

Example code, to issue BLKBSZGET through IORING_OP_URING_CMD:

struct block_uring_cmd {
	__u32	ioctl_cmd;
	__u32	unused1;
	__u64	unused2[4];
};

static int get_bs(struct io_uring *ring, const char *dev)
{
	struct io_uring_cqe *cqe;
	struct io_uring_sqe *sqe;
        struct io_uring_cmd_sqe *csqe;
	struct block_uring_cmd *cmd;
	int ret, fd;

	fd = open(dev, O_RDONLY);

	sqe = io_uring_get_sqe(ring);
	csqe = (void *) sqe;
        memset(csqe, 0, sizeof(*csqe));
        csqe->hdr.opcode = IORING_OP_URING_CMD;
        csqe->hdr.fd = fd;
	csqe->user_data = 0x1234;
	csqe->op = BLOCK_URING_OP_IOCTL;

	io_uring_submit(ring);
	io_uring_wait_cqe(ring, &cqe);
	printf("bs=%d\n", cqe->res);
	io_uring_cqe_seen(ring, cqe);
	return 0;
err:
	return 1;
}

Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
 fs/block_dev.c         | 20 ++++++++++++++++++++
 include/linux/blkdev.h | 11 +++++++++++
 2 files changed, 31 insertions(+)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index cbc403ad0330..9e44f63a0fe1 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -318,11 +318,31 @@ struct blkdev_dio {
 
 static struct bio_set blkdev_dio_pool;
 
+static int blkdev_uring_ioctl(struct block_device *bdev,
+			      struct io_uring_cmd *cmd)
+{
+	struct block_uring_cmd *bcmd = (struct block_uring_cmd *) &cmd->pdu;
+
+	switch (bcmd->ioctl_cmd) {
+	case BLKBSZGET:
+		return block_size(bdev);
+	default:
+		return -ENOTTY;
+	}
+}
+
 static int blkdev_uring_cmd(struct io_uring_cmd *cmd,
 			    enum io_uring_cmd_flags flags)
 {
 	struct block_device *bdev = I_BDEV(cmd->file->f_mapping->host);
 
+	switch (cmd->op) {
+	case BLOCK_URING_OP_IOCTL:
+		return blkdev_uring_ioctl(bdev, cmd);
+	default:
+		break;
+	}
+
 	return blk_uring_cmd(bdev, cmd, flags);
 }
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 7eb993e82783..fa895aa3b51a 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -44,6 +44,17 @@ struct blk_queue_stats;
 struct blk_stat_callback;
 struct blk_keyslot_manager;
 
+enum {
+	BLOCK_URING_OP_IOCTL = 1,
+};
+
+/* This overlays struct io_uring_cmd pdu (40 bytes) */
+struct block_uring_cmd {
+	__u32	ioctl_cmd;
+	__u32	unused1;
+	__u64	unused2[4];
+};
+
 #define BLKDEV_MIN_RQ	4
 #define BLKDEV_MAX_RQ	128	/* Default maximum */
 
-- 
2.31.0