lib: Add 'prefs' API

This defines and reads configuration files that can be used to customize
UHD's behaviour. On Unix systems, they default to:

/etc/uhd/uhd.conf
$APPDATA/.uhd/uhd.conf

On Windows systems, it will look in:

%ProgramData%/uhd/uhd.conf
%AppData%/.uhd/uhd.conf

1 files changed, 54 insertions, 0 deletions

diff --git a/host/lib/include/uhdlib/utils/prefs.hpp b/host/lib/include/uhdlib/utils/prefs.hpp
new file mode 100644
index 000000000..62831a875
--- /dev/null
+++ b/host/lib/include/uhdlib/utils/prefs.hpp
@@ -0,0 +1,54 @@
+//
+// Copyright 2018 Ettus Research, a National Instruments Company
+//
+// SPDX-License-Identifier: GPL-3.0+
+//
+
+#ifndef INCLUDED_LIBUHD_UTILS_PREFS_HPP
+#define INCLUDED_LIBUHD_UTILS_PREFS_HPP
+
+#include <uhd/types/device_addr.hpp>
+#include <uhdlib/utils/config_parser.hpp>
+#include <string>
+
+namespace uhd { namespace prefs {
+
+    /*! Return a reference to an object representing the UHD config file
+     *  state.
+     *
+     * Note: Don't call this in static initializers.
+     */
+    config_parser& get_uhd_config();
+
+    /*! Convenience function to update device args with settings from
+     *  config files.
+     *
+     * Assume the user has a configuration file as such:
+     * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.ini}
+     * [type=b200]
+     * master_clock_rate=20e6
+     *
+     * [serial=f42f9b] ; Let's assume this is another B200
+     * master_clock_rate=10e6
+     * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+     * If get_usrp_args() gets called with "type" key equal to "b200", it will
+     * first apply the `master_clock_rate=20e6` settings, as if they had been
+     * passed in as device args into the initialization sequence. If the device
+     * happens to have the serial number listed above, i.e., "serial" equals
+     * "f42f9b", then the new value `master_clock_rate=10e6` will get applied.
+     *
+     * If the user actually specified their own value of `master_clock_rate`,
+     * that value would get applied.
+     *
+     *
+     * \param user_args After getting the device args from the config
+     *                  files, all of these key/value pairs will be applied
+     *                  and will overwrite the settings from config files
+     *                  if they exist.
+     */
+    uhd::device_addr_t get_usrp_args(const uhd::device_addr_t &user_args);
+
+}} /* namespace uhd::prefs */
+
+#endif /* INCLUDED_LIBUHD_UTILS_PREFS_HPP */
+