+/**
+ * Write a buffer to a non-blocking file descriptor.
+ *
+ * \param fd The file descriptor.
+ * \param buf the buffer to write.
+ * \param len the number of bytes of \a buf.
+ * \param max_bytes_per_write Do not write more than that many bytes at once.
+ *
+ * If \a max_bytes_per_write is non-zero, do not send more than that many bytes
+ * per write().
+ *
+ * EAGAIN is not considered an error condition. For example CCID3 has a
+ * sending wait queue which fills up and is emptied asynchronously. The EAGAIN
+ * case means that there is currently no space in the wait queue, but this can
+ * change at any moment.
+ *
+ * \return Negative on errors, number of bytes written else.
+ */
+int write_nonblock(int fd, const char *buf, size_t len,
+ size_t max_bytes_per_write)
+{
+ size_t written = 0;
+ int ret = 0;
+
+ while (written < len) {
+ size_t num = len - written;
+
+ if (max_bytes_per_write && max_bytes_per_write < num)
+ num = max_bytes_per_write;
+ ret = write(fd, buf + written, num);
+ if (ret < 0 && errno == EAGAIN)
+ return written;
+ if (ret < 0)
+ return -ERRNO_TO_PARA_ERROR(errno);
+ written += ret;
+ }
+ return written;
+}
+
+/**
+ * Simple wrapper for readv().
+ *
+ * \param fd The file descriptor to read from.
+ * \param iov Scatter/gather array used in readv().
+ * \param iovcnt Number of elements in \a iov.
+ *
+ * \return A negative error code on errors, the return value of the underlying
+ * call to readv() otherwise.
+ *
+ * \sa readv(2).
+ */
+int para_readv(int fd, struct iovec *iov, int iovcnt)
+{
+ int ret = readv(fd, iov, iovcnt);
+
+ if (ret < 0)
+ return -ERRNO_TO_PARA_ERROR(errno);
+ return ret;
+}
+