fs: convert core functions to zero_user_page

It's very common for file systems to need to zero part or all of a page,
the simplist way is just to use kmap_atomic() and memset().  There's
actually a library function in include/linux/highmem.h that does exactly
that, but it's confusingly named memclear_highpage_flush(), which is
descriptive of *how* it does the work rather than what the *purpose* is.
So this patchset renames the function to zero_user_page(), and calls it
from the various places that currently open code it.

This first patch introduces the new function call, and converts all the
core kernel callsites, both the open-coded ones and the old
memclear_highpage_flush() ones.  Following this patch is a series of
conversions for each file system individually, per AKPM, and finally a
patch deprecating the old call.  The diffstat below shows the entire
patchset.

[akpm@linux-foundation.org: fix a few things]
Signed-off-by: Nate Diller <nate.diller@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 19 insertions, 9 deletions

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index a515eb0afdfb..b5f2ab42d984 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -94,17 +94,27 @@ static inline void clear_highpage(struct page *page)
 
 /*
  * Same but also flushes aliased cache contents to RAM.
+ *
+ * This must be a macro because KM_USER0 and friends aren't defined if
+ * !CONFIG_HIGHMEM
  */
-static inline void memclear_highpage_flush(struct page *page, unsigned int offset, unsigned int size)
+#define zero_user_page(page, offset, size, km_type)             \
+        do {                                                    \
+                void *kaddr;                                    \
+                                                                \
+                BUG_ON((offset) + (size) > PAGE_SIZE);          \
+                                                                \
+                kaddr = kmap_atomic(page, km_type);             \
+                memset((char *)kaddr + (offset), 0, (size));    \
+                flush_dcache_page(page);                        \
+                kunmap_atomic(kaddr, (km_type));                \
+        } while (0)
+
+
+static inline void memclear_highpage_flush(struct page *page,
+                        unsigned int offset, unsigned int size)
 {
-        void *kaddr;
-
-        BUG_ON(offset + size > PAGE_SIZE);
-
-        kaddr = kmap_atomic(page, KM_USER0);
-        memset((char *)kaddr + offset, 0, size);
-        flush_dcache_page(page);
-        kunmap_atomic(kaddr, KM_USER0);
+        zero_user_page(page, offset, size, KM_USER0);
 }
 
 #ifndef __HAVE_ARCH_COPY_USER_HIGHPAGE