io_uring/mock: add cmd using vectored regbufs

There is a command api allowing to import vectored registered buffers,
add a new mock command that uses the feature and simply copies the
specified registered buffer into user space or vice versa.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/229a113fd7de6b27dbef9567f7c0bf4475c9017d.1750599274.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/uapi/linux/io_uring/mock_file.h

@@ -3,6 +3,12 @@
 
 #include <linux/types.h>
 
+enum {
+	IORING_MOCK_FEAT_CMD_COPY,
+
+	IORING_MOCK_FEAT_END,
+};
+
 struct io_uring_mock_probe {
 	__u64		features;
 	__u64		__resv[9];
@@ -19,4 +25,12 @@ enum {
 	IORING_MOCK_MGR_CMD_CREATE,
 };
 
+enum {
+	IORING_MOCK_CMD_COPY_REGBUF,
+};
+
+enum {
+	IORING_MOCK_COPY_FROM			= 1,
+};
+
 #endif

io_uring/mock_file.c

@@ -9,8 +9,76 @@
 #include <linux/io_uring_types.h>
 #include <uapi/linux/io_uring/mock_file.h>
 
+#define IO_VALID_COPY_CMD_FLAGS		IORING_MOCK_COPY_FROM
+
+static int io_copy_regbuf(struct iov_iter *reg_iter, void __user *ubuf)
+{
+	size_t ret, copied = 0;
+	size_t buflen = PAGE_SIZE;
+	void *tmp_buf;
+
+	tmp_buf = kzalloc(buflen, GFP_KERNEL);
+	if (!tmp_buf)
+		return -ENOMEM;
+
+	while (iov_iter_count(reg_iter)) {
+		size_t len = min(iov_iter_count(reg_iter), buflen);
+
+		if (iov_iter_rw(reg_iter) == ITER_SOURCE) {
+			ret = copy_from_iter(tmp_buf, len, reg_iter);
+			if (ret <= 0)
+				break;
+			if (copy_to_user(ubuf, tmp_buf, ret))
+				break;
+		} else {
+			if (copy_from_user(tmp_buf, ubuf, len))
+				break;
+			ret = copy_to_iter(tmp_buf, len, reg_iter);
+			if (ret <= 0)
+				break;
+		}
+		ubuf += ret;
+		copied += ret;
+	}
+
+	kfree(tmp_buf);
+	return copied;
+}
+
+static int io_cmd_copy_regbuf(struct io_uring_cmd *cmd, unsigned int issue_flags)
+{
+	const struct io_uring_sqe *sqe = cmd->sqe;
+	const struct iovec __user *iovec;
+	unsigned flags, iovec_len;
+	struct iov_iter iter;
+	void __user *ubuf;
+	int dir, ret;
+
+	ubuf = u64_to_user_ptr(READ_ONCE(sqe->addr3));
+	iovec = u64_to_user_ptr(READ_ONCE(sqe->addr));
+	iovec_len = READ_ONCE(sqe->len);
+	flags = READ_ONCE(sqe->file_index);
+
+	if (unlikely(sqe->ioprio || sqe->__pad1))
+		return -EINVAL;
+	if (flags & ~IO_VALID_COPY_CMD_FLAGS)
+		return -EINVAL;
+
+	dir = (flags & IORING_MOCK_COPY_FROM) ? ITER_SOURCE : ITER_DEST;
+	ret = io_uring_cmd_import_fixed_vec(cmd, iovec, iovec_len, dir, &iter,
+					    issue_flags);
+	if (ret)
+		return ret;
+	ret = io_copy_regbuf(&iter, ubuf);
+	return ret ? ret : -EFAULT;
+}
+
 static int io_mock_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
 {
+	switch (cmd->cmd_op) {
+	case IORING_MOCK_CMD_COPY_REGBUF:
+		return io_cmd_copy_regbuf(cmd, issue_flags);
+	}
 	return -ENOTSUPP;
 }
 
@@ -91,7 +159,7 @@ static int io_probe_mock(struct io_uring_cmd *cmd)
 	if (!mem_is_zero(&mp, sizeof(mp)))
 		return -EINVAL;
 
-	mp.features = 0;
+	mp.features = IORING_MOCK_FEAT_END;
 
 	if (copy_to_user(uarg, &mp, uarg_size))
 		return -EFAULT;