Wrong comment due to pte_file()

Wrong comment due to pte_file()

[Pete Zaitcev]

The comment above other bit tests says "if pte_present is true",
but the pte_file is backwards. A classic case of code changing
from under comments. How about abolishing all comments? :-)

diff -urN -X dontdiff linux-2.5.66/include/asm-i386/pgtable.h linux-2.5.66-sparc/include/asm-i386/pgtable.h
--- linux-2.5.66/include/asm-i386/pgtable.h	2003-03-24 14:01:14.000000000 -0800
+++ linux-2.5.66-sparc/include/asm-i386/pgtable.h	2003-03-30 16:35:04.000000000 -0800
@@ -188,6 +188,10 @@
 static inline int pte_dirty(pte_t pte)		{ return (pte).pte_low & _PAGE_DIRTY; }
 static inline int pte_young(pte_t pte)		{ return (pte).pte_low & _PAGE_ACCESSED; }
 static inline int pte_write(pte_t pte)		{ return (pte).pte_low & _PAGE_RW; }
+
+/*
+ * The following only works if pte_present() is not true.
+ */
 static inline int pte_file(pte_t pte)		{ return (pte).pte_low & _PAGE_FILE; }
 
 static inline pte_t pte_rdprotect(pte_t pte)	{ (pte).pte_low &= ~_PAGE_USER; return pte; }

Re: Wrong comment due to pte_file()

[Andrew Morton]

Pete Zaitcev <zaitcev@redhat.com> wrote:
>
> How about abolishing all comments?

Or all code.

> --- linux-2.5.66/include/asm-i386/pgtable.h	2003-03-24 14:01:14.000000000 -0800
> +++ linux-2.5.66-sparc/include/asm-i386/pgtable.h	2003-03-30 16:35:04.000000000 -0800

Thanks.  There's another bogus comment doing the rounds as well:

#define _PAGE_FILE      0x040   /* pagecache or swap */

This is exactly wrong - this bit is used to distinguish pagecache from swap. 
See handle_pte_fault():


	if (pte_file(entry))
		return do_file_page(mm, vma, address, write_access, pte, pmd);
	return do_swap_page(mm, vma, address, pte, pmd, entry, write_access);


Some architectures got sneaky:

#define _PAGE_FILE  0x80000 /* pagecache or swap? */

ah-hah!  That question mark *totally* changes the meaning and reveals all.

Pity those who follow after us.  I shall fix it up.