Re: [PATCH 0/13] maps: pagemap, kpagemap, and related cleanups

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Andrew Morton wrote:
On Thu, 12 Apr 2007 16:10:50 -0700
William Lee Irwin III <[email protected]> wrote:

+       while (count > 0) {
+               chunk = min_t(size_t, count, PAGE_SIZE);
+               i = 0;
+
+               if (pfn == -1) {
+                       page[0] = 0;
+                       page[1] = 0;
+                       ((char *)page)[0] = (ntohl(1) != 1);


OK.


+                       ((char *)page)[1] = PAGE_SHIFT;


OK.

Shouldn't we just expose page size and endianness by other means? (another file or
syscall).

+               for (; i < 2 * chunk / KPMSIZE; i += 2, pfn++) {
+                       ppage = pfn_to_page(pfn);
+                       if (!ppage) {
+                               page[i] = 0;
+                               page[i + 1] = 0;
+                       } else {
+                               page[i] = ppage->flags;
+                               page[i + 1] = atomic_read(&ppage->_count);
+                       }
+               }


Not a good idea to expose raw flags in this manner - it changes at the drop
of a hat.  We'd need to also expose the kernel's PG_foo-to-bitnumber
mapping to make this viable.

I don't think it is viable because that makes the flags part of the
userspace ABI. I wonder what they are needed for.

--
SUSE Labs, Novell Inc.
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