This patch fixes in st.c the bug in the signed/unsigned int comparison

reported by Doug Gilbert and fixed by him in sg.c (see [PATCH] sg direct
io/mmap oops). Doug fixed the comparison in sg.c. This fix for st.c does not
touch the comparison but makes both arguments signed to remove the
problem. The new code is adapted from linux/fs/bio.c.
Signed-off-by: Kai Makisara <kai.makisara@kolumbus.fi>

Rejections fixed up and
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/st.c

@@ -17,7 +17,7 @@
    Last modified: 18-JAN-1998 Richard Gooch <rgooch@atnf.csiro.au> Devfs support
  */
 
-static char *verstr = "20050802";
+static char *verstr = "20050830";
 
 #include <linux/module.h>
 
@@ -4444,12 +4444,12 @@ static int st_map_user_pages(struct scatterlist *sgl, const unsigned int max_pag
 static int sgl_map_user_pages(struct scatterlist *sgl, const unsigned int max_pages, 
 			      unsigned long uaddr, size_t count, int rw)
 {
+	unsigned long end = (uaddr + count + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	unsigned long start = uaddr >> PAGE_SHIFT;
+	const int nr_pages = end - start;
 	int res, i, j;
-	unsigned int nr_pages;
 	struct page **pages;
 
-	nr_pages = ((uaddr & ~PAGE_MASK) + count + ~PAGE_MASK) >> PAGE_SHIFT;
-
 	/* User attempted Overflow! */
 	if ((uaddr + count) < uaddr)
 		return -EINVAL;