On Tue, 12 Jun 2007, Luck, Tony wrote:
> Raising the PAGE_SIZE to 64k does generate a couple of
> new warnings in the build:
>
> drivers/usb/core/devio.c:632: warning: comparison is always false due to
> limited range of data type
> fs/fat/inode.c:1227: warning: comparison is always false due to limited range
> of data type
>
> Both of these are due to range comparisons of u16 data types
> with PAGE_SIZE. They both look harmless ... we'll get an
> infinitessimal performance boost from the compiler dropping
> the code, but it is annoying to add these to the (already
> large) list of warnings to ignore.
>
> Anyone got any cute ideas on how to make these warnings
> go away?
Talk to the powerpc guys? They also support 64k page size.
The obvious solution is to put an (ugly) #ifdef around it:
Index: linux-2.6/drivers/usb/core/devio.c
===================================================================
--- linux-2.6.orig/drivers/usb/core/devio.c 2007-06-12 10:58:57.000000000
-0700
+++ linux-2.6/drivers/usb/core/devio.c 2007-06-12 11:02:19.000000000 -0700
@@ -629,8 +629,14 @@ static int proc_control(struct dev_state
return -EFAULT;
if ((ret = check_ctrlrecip(ps, ctrl.bRequestType, ctrl.wIndex)))
return ret;
+#if PAGE_SIZE < 65536
+ /*
+ * ctrl.wLength is a 16 bit value that cannot be greater
+ * than page size if PAGE_SIZE >= 64k.
+ */
if (ctrl.wLength > PAGE_SIZE)
return -EINVAL;
+#endif
if (!(tbuf = (unsigned char *)__get_free_page(GFP_KERNEL)))
return -ENOMEM;
tmo = ctrl.timeout;
Index: linux-2.6/fs/fat/inode.c
===================================================================
--- linux-2.6.orig/fs/fat/inode.c 2007-06-12 10:59:53.000000000 -0700
+++ linux-2.6/fs/fat/inode.c 2007-06-12 11:01:17.000000000 -0700
@@ -1223,8 +1223,15 @@ int fat_fill_super(struct super_block *s
logical_sector_size =
le16_to_cpu(get_unaligned((__le16 *)&b->sector_size));
if (!is_power_of_2(logical_sector_size)
- || (logical_sector_size < 512)
- || (PAGE_CACHE_SIZE < logical_sector_size)) {
+#if PAGE_SIZE < 65536
+ /*
+ * Logical sector size is a 16 bit value.
+ * If the page size is 64k or higher then the comparison
+ * is always true.
+ */
+ || (PAGE_CACHE_SIZE < logical_sector_size)
+#endif
+ || (logical_sector_size < 512)) {
if (!silent)
printk(KERN_ERR "FAT: bogus logical sector size %u\n",
logical_sector_size);
-
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