sys/shell: initial XFA support

sys/include/shell.h

@@ -24,6 +24,7 @@
 #include "periph/pm.h"
 
 #include "kernel_defines.h"
+#include "xfa.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -196,6 +197,37 @@ static inline void shell_run(const shell_command_t *commands,
     shell_run_forever(commands, line_buf, len);
 }
 
+/**
+ * @brief   Define shell command
+ *
+ * This macro is a helper for defining a shell command and adding it to the
+ * shell commands XFA (cross file array).
+ *
+ * Shell commands added using this macros will be sorted *after* builtins and
+ * commands passed via parameter to `shell_run_once()`. If a command with the
+ * same name exists in any of those, they will make a command added via this
+ * macro inaccassible.
+ *
+ * Commands added with this macro will be sorted alphanumerically by `name`.
+ *
+ * @experimental This should be considered experimental API, subject to change
+ *               without notice!
+ *
+ * Example:
+ *
+ * ```.c
+ * #include "shell.h"
+ * static int _my_command(int argc, char **argv) {
+ *   // ...
+ * }
+ * SHELL_COMMAND(my_command, "my command help text", _my_command);
+ * ```
+ */
+#define SHELL_COMMAND(name, help, func) \
+    XFA_USE_CONST(shell_command_t*, shell_commands_xfa); \
+    static const shell_command_t _xfa_ ## name ## _cmd = { #name, help, &func }; \
+    XFA_ADD_PTR(shell_commands_xfa, name, name, &_xfa_ ## name ## _cmd)
+
 #ifdef __cplusplus
 }
 #endif

sys/shell/shell.c

@@ -36,9 +36,13 @@
 #include <errno.h>
 
 #include "kernel_defines.h"
+#include "xfa.h"
 #include "shell.h"
 #include "shell_commands.h"
 
+/* define shell command cross file array */
+XFA_INIT_CONST(shell_command_t*, shell_commands_xfa);
+
 #define ETX '\x03'  /** ASCII "End-of-Text", or Ctrl-C */
 #define EOT '\x04'  /** ASCII "End-of-Transmission", or Ctrl-D */
 #define BS  '\x08'  /** ASCII "Backspace" */
@@ -92,6 +96,19 @@ static shell_command_handler_t search_commands(const shell_command_t *entry,
     return NULL;
 }
 
+static shell_command_handler_t search_commands_xfa(char *command)
+{
+    unsigned n = XFA_LEN(shell_command_t*, shell_commands_xfa);
+
+    for (unsigned i = 0; i < n; i++) {
+        const volatile shell_command_t *entry = shell_commands_xfa[i];
+        if (strcmp(entry->name, command) == 0) {
+            return entry->handler;
+        }
+    }
+    return NULL;
+}
+
 static shell_command_handler_t find_handler(
         const shell_command_t *command_list, char *command)
 {
@@ -104,6 +121,10 @@ static shell_command_handler_t find_handler(
         handler = search_commands(_builtin_cmds, command);
     }
 
+    if (handler == NULL) {
+        handler = search_commands_xfa(command);
+    }
+
     return handler;
 }
 
@@ -114,6 +135,15 @@ static void print_commands(const shell_command_t *entry)
     }
 }
 
+static void print_commands_xfa(void)
+{
+    unsigned n = XFA_LEN(shell_command_t*, shell_commands_xfa);
+    for (unsigned i = 0; i < n; i++) {
+        const volatile shell_command_t *entry = shell_commands_xfa[i];
+        printf("%-20s %s\n", entry->name, entry->desc);
+    }
+}
+
 static void print_help(const shell_command_t *command_list)
 {
     puts("Command              Description"
@@ -125,6 +155,8 @@ static void print_help(const shell_command_t *command_list)
     if (_builtin_cmds != NULL) {
         print_commands(_builtin_cmds);
     }
+
+    print_commands_xfa();
 }
 
 /**