Updated comments

fs/vfs/fs_ioctl.c

@@ -69,7 +69,7 @@
  *
  * Return:
  *   >=0 on success (positive non-zero values are cmd-specific)
- *   -1 on failure withi errno set properly:
+ *   -1 on failure with errno set properly:
  *
  *   EBADF
  *     'fd' is not a valid descriptor.

include/nuttx/fs/fs.h

@@ -638,7 +638,7 @@ int close_blockdriver(FAR struct inode *inode);
  *
  * Return:
  *   >=0 on success (positive non-zero values are cmd-specific)
- *   -1 on failure withi errno set properly:
+ *   -1 on failure with errno set properly:
  *
  *   EBADF
  *     'fd' is not a valid descriptor.

include/sys/ioctl.h

@@ -84,7 +84,7 @@ extern "C"
  *
  * Return:
  *   >=0 on success (positive non-zero values are cmd-specific)
- *   -1 on failure withi errno set properly:
+ *   -1 on failure with errno set properly:
  *
  *   EBADF
  *     'fd' is not a valid descriptor.

libc/Kconfig

@@ -76,7 +76,20 @@ config LIBC_IOCTL_VARIADIC
 
 		WARNING:  Use of this option could cause subtle system errors is
 		the third argument is omitted or if the sizeof the thread argument
-		is anything other than sizeof (unsigned long).
+		is anything other than sizeof (unsigned long).  Most small integers
+		will be promoted to 'int'.  The following assertion appears in ioctl():
+
+			DEBUGASSERT(sizeof(int)        == sizeof(unsigned long) &&
+			            sizeof(FAR void *) == sizeof(unsigned long));
+
+		Do not enable this option if the above is not true.  32-bit ARM
+		should pass this test with all three types having sizeof(type) == 4
+		bytes.  'float' should also be tested.  But 'long long' and 'double'
+		are out of the question!  Don't event try to pass them.
+
+		And what will happen if no third argument is passed?  In most cases,
+		this should just result in a garbage value for arg.  But you may
+		discover cases where something worse happens!
 
 config LIB_RAND_ORDER
 	int "Order of the random number generate"

libc/misc/lib_ioctl.c

@@ -42,6 +42,7 @@
 #include <sys/ioctl.h>
 #include <stdarg.h>
 #include <errno.h>
+#include <assert.h>
 
 #include <nuttx/fs/fs.h>
 
@@ -66,7 +67,7 @@
  *
  * Return:
  *   >=0 on success (positive non-zero values are cmd-specific)
- *   -1 on failure withi errno set properly:
+ *   -1 on failure with errno set properly:
  *
  *   EBADF
  *     'fd' is not a valid descriptor.
@@ -84,15 +85,26 @@
 
 int ioctl(int fd, int req, ...)
 {
-  va_list ap;
   unsigned long arg;
+  va_list ap;
 
   /* Get the unsigned long argument.
    *
-   * REVISIT:  This could cause of the crash down the road if the actual size
+   * REVISIT:  This could be the cause of the crash down the road if the
-   * of the argument is anything other than sizeof(unsigned long);
+   * actual size of the argument is anything other than sizeof(unsigned long).
+   * Most small integers will be promoted to 'int'.  ARM should pass the
+   * following test with all three types having sizeof(type) == 4 bytes.
+   * 'float' should also be tested.  But 'long long' and 'double' are out of
+   * the question!  Don't try to pass them.
+   *
+   * And what will happen if no third argument is passed?  In most cases,
+   * this should just result in a garbage value for arg.  But you may
+   * discover cases where something worse happens!
    */
 
+  DEBUGASSERT(sizeof(int)        == sizeof(unsigned long) &&
+              sizeof(FAR void *) == sizeof(unsigned long));
+
   va_start(ap, req);
   arg = va_arg(ap, unsigned long);
   va_end(ap);