Add a callback function to userboot.so to fetch a list of environment

variables and pass them to the kernel.

Bump up the userboot version to USERBOOT_VERSION_3. This takes into account
the bump to USERBOOT_VERSION_2 that has already happened in head (but not
propagated to this branch yet).

Reviewed by:	dfr@
Obtained from:	NetApp

sys/boot/userboot/test/test.c

@@ -339,6 +339,18 @@ test_getmem(void *arg, uint64_t *lowmem, uint64_t *highmem)
         *highmem = 0;
 }
 
+const char *
+test_getenv(void *arg, int idx)
+{
+	static const char *vars[] = {
+		"foo=bar",
+		"bar=barbar",
+		NULL
+	};
+
+	return (vars[idx]);
+}
+
 struct loader_callbacks_v1 cb = {
 	.putc = test_putc,
 	.getc = test_getc,
@@ -365,6 +377,8 @@ struct loader_callbacks_v1 cb = {
 	.delay = test_delay,
 	.exit = test_exit,
         .getmem = test_getmem,
+
+	.getenv = test_getenv,
 };
 
 void
@@ -424,5 +438,5 @@ main(int argc, char** argv)
 	term.c_lflag &= ~(ICANON|ECHO);
 	tcsetattr(0, TCSAFLUSH, &term);
 
-	func(&cb, NULL, USERBOOT_VERSION_1, disk_fd >= 0);
+	func(&cb, NULL, USERBOOT_VERSION_3, disk_fd >= 0);
 }

sys/boot/userboot/userboot.h

@@ -29,7 +29,7 @@
 /*
  * USERBOOT interface versions
  */
-#define	USERBOOT_VERSION_1      1
+#define	USERBOOT_VERSION_3      3
 
 /*
  * Exit codes from the loader
@@ -175,4 +175,16 @@ struct loader_callbacks_v1 {
          */
 	void		(*getmem)(void *arg, uint64_t *lowmem,
             uint64_t *highmem);
+
+	/*
+	 * Returns an environment variable in the form "name=value".
+	 *
+	 * If there are no more variables that need to be set in the
+	 * loader environment then return NULL.
+	 *
+	 * 'num' is used as a handle for the callback to identify which
+	 * environment variable to return next. It will begin at 0 and
+	 * each invocation will add 1 to the previous value of 'num'.
+	 */
+	const char *	(*getenv)(void *arg, int num);
 };

sys/boot/userboot/userboot/main.c

@@ -68,9 +68,10 @@ void
 loader_main(struct loader_callbacks_v1 *cb, void *arg, int version, int ndisks)
 {
 	static char malloc[1024*1024];
+	const char *var;
 	int i;
 
-        if (version != USERBOOT_VERSION_1)
+        if (version != USERBOOT_VERSION_3)
                 abort();
 
 	callbacks = cb;
@@ -105,6 +106,17 @@ loader_main(struct loader_callbacks_v1 *cb, void *arg, int version, int ndisks)
 
 	setenv("LINES", "24", 1);	/* optional */
 
+	/*
+	 * Set custom environment variables
+	 */
+	i = 0;
+	while (1) {
+		var = CALLBACK(getenv, i++);
+		if (var == NULL)
+			break;
+		putenv(var);
+	}
+
 	archsw.arch_autoload = userboot_autoload;
 	archsw.arch_getdev = userboot_getdev;
 	archsw.arch_copyin = userboot_copyin;