Add the concept of a "user pointer" (similar to the void __user * in

the kernel), which encapsulates the information needed to refer to an
external buffer.  Under normal operation, this can just be a void *
equivalent, but under -DKEEP_IT_REAL it would be a segoff_t equivalent.

Use this concept to avoid the need for bounce buffers in int13.c,
which reduces memory usage and opens up the possibility of using
multi-sector reads.

Extend the block-device API and the SCSI block device implementation
to support multi-sector reads.

Update iscsi.c to use user buffers.

Move the obsolete portions of realmode.h to old_realmode.h.

MS-DOS now boots an order of magnitude faster over iSCSI (~10 seconds
from power-up to C:> prompt in bochs).

src/arch/i386/include/bits/uaccess.h

@@ -0,0 +1,6 @@
+#ifndef _BITS_UACCESS_H
+#define _BITS_UACCESS_H
+
+#include <realmode.h>
+
+#endif /* _BITS_UACCESS_H */

src/arch/i386/include/librm.h

@@ -92,6 +92,69 @@ copy_from_real_librm ( void *dest, unsigned int src_seg,
 #define put_real put_real_librm
 #define get_real get_real_librm
 
+/**
+ * A pointer to a user buffer
+ *
+ * Even though we could just use a void *, we use an intptr_t so that
+ * attempts to use normal pointers show up as compiler warnings.  Such
+ * code is actually valid for librm, but not for libkir (i.e. under
+ * KEEP_IT_REAL), so it's good to have the warnings even under librm.
+ */
+typedef intptr_t userptr_t;
+
+/**
+ * Copy data to user buffer
+ *
+ * @v buffer	User buffer
+ * @v offset	Offset within user buffer
+ * @v src	Source
+ * @v len	Length
+ */
+static inline __attribute__ (( always_inline )) void
+copy_to_user ( userptr_t buffer, off_t offset, const void *src, size_t len ) {
+	memcpy ( ( void * ) buffer + offset, src, len );
+}
+
+/**
+ * Copy data from user buffer
+ *
+ * @v dest	Destination
+ * @v buffer	User buffer
+ * @v offset	Offset within user buffer
+ * @v len	Length
+ */
+static inline __attribute__ (( always_inline )) void
+copy_from_user ( void *dest, userptr_t buffer, off_t offset, size_t len ) {
+	memcpy ( dest, ( void * ) buffer + offset, len );
+}
+
+/**
+ * Convert virtual address to user buffer
+ *
+ * @v virtual	Virtual address
+ * @ret buffer	User buffer
+ *
+ * This constructs a user buffer from an ordinary pointer.  Use it
+ * when you need to pass a pointer to an internal buffer to a function
+ * that expects a @c userptr_t.
+ */
+static inline __attribute__ (( always_inline )) userptr_t
+virt_to_user ( void * virtual ) {
+	return ( ( intptr_t ) virtual );
+}
+
+/**
+ * Convert segment:offset address to user buffer
+ *
+ * @v segment	Real-mode segment
+ * @v offset	Real-mode offset
+ * @ret buffer	User buffer
+ */
+static inline __attribute__ (( always_inline )) userptr_t
+real_to_user ( unsigned int segment, unsigned int offset ) {
+	return virt_to_user ( VIRTUAL ( segment, offset ) );
+}
+
 /* Copy to/from real-mode stack */
 extern uint16_t copy_to_rm_stack ( void *data, size_t size );
 extern void remove_from_rm_stack ( void *data, size_t size );

src/arch/i386/include/old_realmode.h

@@ -0,0 +1,22 @@
+#ifndef _OLD_REALMODE_H
+#define _OLD_REALMODE_H
+
+#include <realmode.h>
+
+#warning "Anything including this header is obsolete and must be rewritten"
+
+/* Just for now */
+#define SEGMENT(x) ( virt_to_phys ( x ) >> 4 )
+#define OFFSET(x) ( virt_to_phys ( x ) & 0xf )
+#define SEGOFF(x) { OFFSET(x), SEGMENT(x) }
+
+/* To make basemem.c compile */
+extern int lock_real_mode_stack;
+extern char *real_mode_stack;
+extern char real_mode_stack_size[];
+
+#define RM_FRAGMENT(name,asm) \
+	void name ( void ) {} \
+	extern char name ## _size[];
+
+#endif /* _OLD_REALMODE_H */

src/arch/i386/include/realmode.h

@@ -149,25 +149,6 @@ typedef struct segoff segoff_t;
  * "(discard)" in the above code.
  */
 
-#warning "realmode.h contains placeholders for obsolete macros"
-
-
-/* Just for now */
-#define SEGMENT(x) ( virt_to_phys ( x ) >> 4 )
-#define OFFSET(x) ( virt_to_phys ( x ) & 0xf )
-#define SEGOFF(x) { OFFSET(x), SEGMENT(x) }
-
-/* To make basemem.c compile */
-extern int lock_real_mode_stack;
-extern char *real_mode_stack;
-extern char real_mode_stack_size[];
-
-#define RM_FRAGMENT(name,asm) \
-	void name ( void ) {} \
-	extern char name ## _size[];
-
-
-
 #endif /* ASSEMBLY */
 
 #endif /* REALMODE_H */