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, 2 insertions, 6 deletions

diff --git a/fs/direct-io.c b/fs/direct-io.c
index d9d0833444f..8aa2d8b04ef 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -867,7 +867,6 @@ static int do_direct_IO(struct dio *dio)
 do_holes:
 			/* Handle holes */
 			if (!buffer_mapped(map_bh)) {
-				char *kaddr;
 				loff_t i_size_aligned;
 
 				/* AKPM: eargh, -ENOTBLK is a hack */
@@ -888,11 +887,8 @@ do_holes:
 					page_cache_release(page);
 					goto out;
 				}
-				kaddr = kmap_atomic(page, KM_USER0);
-				memset(kaddr + (block_in_page << blkbits),
-						0, 1 << blkbits);
-				flush_dcache_page(page);
-				kunmap_atomic(kaddr, KM_USER0);
+				zero_user_page(page, block_in_page << blkbits,
+						1 << blkbits, KM_USER0);
 				dio->block_in_file++;
 				block_in_page++;
 				goto next_block;