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>

7 files changed, 42 insertions, 81 deletions

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index af6d7274a7cc..18cdd8c77626 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -243,17 +243,13 @@ static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec,
                 transfer_result = lo_do_transfer(lo, WRITE, page, offset,
                                 bvec->bv_page, bv_offs, size, IV);
                 if (unlikely(transfer_result)) {
-                        char *kaddr;
-
                         /*
                          * The transfer failed, but we still write the data to
                          * keep prepare/commit calls balanced.
                          */
                         printk(KERN_ERR "loop: transfer error block %llu\n",
                                (unsigned long long)index);
-                        kaddr = kmap_atomic(page, KM_USER0);
-                        memset(kaddr + offset, 0, size);
-                        kunmap_atomic(kaddr, KM_USER0);
+                        zero_user_page(page, offset, size, KM_USER0);
                 }
                 flush_dcache_page(page);
                 ret = aops->commit_write(file, page, offset,
diff --git a/fs/buffer.c b/fs/buffer.c
index eb820b82a636..fc2d763a8d78 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1846,13 +1846,8 @@ static int __block_prepare_write(struct inode *inode, struct page *page,
                 if (block_start >= to)
                         break;
                 if (buffer_new(bh)) {
-                        void *kaddr;
-
                         clear_buffer_new(bh);
-                        kaddr = kmap_atomic(page, KM_USER0);
-                        memset(kaddr+block_start, 0, bh->b_size);
-                        flush_dcache_page(page);
-                        kunmap_atomic(kaddr, KM_USER0);
+                        zero_user_page(page, block_start, bh->b_size, KM_USER0);
                         set_buffer_uptodate(bh);
                         mark_buffer_dirty(bh);
                 }
@@ -1940,10 +1935,8 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
                                         SetPageError(page);
                         }
                         if (!buffer_mapped(bh)) {
-                                void *kaddr = kmap_atomic(page, KM_USER0);
-                                memset(kaddr + i * blocksize, 0, blocksize);
-                                flush_dcache_page(page);
-                                kunmap_atomic(kaddr, KM_USER0);
+                                zero_user_page(page, i * blocksize, blocksize,
+                                                KM_USER0);
                                 if (!err)
                                         set_buffer_uptodate(bh);
                                 continue;
@@ -2086,7 +2079,6 @@ int cont_prepare_write(struct page *page, unsigned offset,
         long status;
         unsigned zerofrom;
         unsigned blocksize = 1 << inode->i_blkbits;
-        void *kaddr;
 
         while(page->index > (pgpos = *bytes>>PAGE_CACHE_SHIFT)) {
                 status = -ENOMEM;
@@ -2108,10 +2100,8 @@ int cont_prepare_write(struct page *page, unsigned offset,
                                                 PAGE_CACHE_SIZE, get_block);
                 if (status)
                         goto out_unmap;
-                kaddr = kmap_atomic(new_page, KM_USER0);
-                memset(kaddr+zerofrom, 0, PAGE_CACHE_SIZE-zerofrom);
-                flush_dcache_page(new_page);
-                kunmap_atomic(kaddr, KM_USER0);
+                zero_user_page(page, zerofrom, PAGE_CACHE_SIZE - zerofrom,
+                                KM_USER0);
                 generic_commit_write(NULL, new_page, zerofrom, PAGE_CACHE_SIZE);
                 unlock_page(new_page);
                 page_cache_release(new_page);
@@ -2138,10 +2128,7 @@ int cont_prepare_write(struct page *page, unsigned offset,
         if (status)
                 goto out1;
         if (zerofrom < offset) {
-                kaddr = kmap_atomic(page, KM_USER0);
-                memset(kaddr+zerofrom, 0, offset-zerofrom);
-                flush_dcache_page(page);
-                kunmap_atomic(kaddr, KM_USER0);
+                zero_user_page(page, zerofrom, offset - zerofrom, KM_USER0);
                 __block_commit_write(inode, page, zerofrom, offset);
         }
         return 0;
@@ -2340,10 +2327,7 @@ failed:
          * Error recovery is pretty slack.  Clear the page and mark it dirty
          * so we'll later zero out any blocks which _were_ allocated.
          */
-        kaddr = kmap_atomic(page, KM_USER0);
-        memset(kaddr, 0, PAGE_CACHE_SIZE);
-        flush_dcache_page(page);
-        kunmap_atomic(kaddr, KM_USER0);
+        zero_user_page(page, 0, PAGE_CACHE_SIZE, KM_USER0);
         SetPageUptodate(page);
         set_page_dirty(page);
         return ret;
@@ -2382,7 +2366,6 @@ int nobh_writepage(struct page *page, get_block_t *get_block,
         loff_t i_size = i_size_read(inode);
         const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
         unsigned offset;
-        void *kaddr;
         int ret;
 
         /* Is the page fully inside i_size? */
@@ -2413,10 +2396,7 @@ int nobh_writepage(struct page *page, get_block_t *get_block,
          * the  page size, the remaining memory is zeroed when mapped, and
          * writes to that region are not written out to the file."
          */
-        kaddr = kmap_atomic(page, KM_USER0);
-        memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
-        flush_dcache_page(page);
-        kunmap_atomic(kaddr, KM_USER0);
+        zero_user_page(page, offset, PAGE_CACHE_SIZE - offset, KM_USER0);
 out:
         ret = mpage_writepage(page, get_block, wbc);
         if (ret == -EAGAIN)
@@ -2437,7 +2417,6 @@ int nobh_truncate_page(struct address_space *mapping, loff_t from)
         unsigned to;
         struct page *page;
         const struct address_space_operations *a_ops = mapping->a_ops;
-        char *kaddr;
         int ret = 0;
 
         if ((offset & (blocksize - 1)) == 0)
@@ -2451,10 +2430,8 @@ int nobh_truncate_page(struct address_space *mapping, loff_t from)
         to = (offset + blocksize) & ~(blocksize - 1);
         ret = a_ops->prepare_write(NULL, page, offset, to);
         if (ret == 0) {
-                kaddr = kmap_atomic(page, KM_USER0);
-                memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
-                flush_dcache_page(page);
-                kunmap_atomic(kaddr, KM_USER0);
+                zero_user_page(page, offset, PAGE_CACHE_SIZE - offset,
+                                KM_USER0);
                 /*
                  * It would be more correct to call aops->commit_write()
                  * here, but this is more efficient.
@@ -2480,7 +2457,6 @@ int block_truncate_page(struct address_space *mapping,
         struct inode *inode = mapping->host;
         struct page *page;
         struct buffer_head *bh;
-        void *kaddr;
         int err;
 
         blocksize = 1 << inode->i_blkbits;
@@ -2534,11 +2510,7 @@ int block_truncate_page(struct address_space *mapping,
                         goto unlock;
         }
 
-        kaddr = kmap_atomic(page, KM_USER0);
-        memset(kaddr + offset, 0, length);
-        flush_dcache_page(page);
-        kunmap_atomic(kaddr, KM_USER0);
-
+        zero_user_page(page, offset, length, KM_USER0);
         mark_buffer_dirty(bh);
         err = 0;
 
@@ -2559,7 +2531,6 @@ int block_write_full_page(struct page *page, get_block_t *get_block,
         loff_t i_size = i_size_read(inode);
         const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
         unsigned offset;
-        void *kaddr;
 
         /* Is the page fully inside i_size? */
         if (page->index < end_index)
@@ -2585,10 +2556,7 @@ int block_write_full_page(struct page *page, get_block_t *get_block,
          * the  page size, the remaining memory is zeroed when mapped, and
          * writes to that region are not written out to the file."
          */
-        kaddr = kmap_atomic(page, KM_USER0);
-        memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
-        flush_dcache_page(page);
-        kunmap_atomic(kaddr, KM_USER0);
+        zero_user_page(page, offset, PAGE_CACHE_SIZE - offset, KM_USER0);
         return __block_write_full_page(inode, page, get_block, wbc);
 }
 
diff --git a/fs/direct-io.c b/fs/direct-io.c
index d9d0833444f5..8aa2d8b04ef1 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;
diff --git a/fs/mpage.c b/fs/mpage.c
index fa2441f57b41..0fb914fc2ee0 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -284,11 +284,9 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
         }
 
         if (first_hole != blocks_per_page) {
-                char *kaddr = kmap_atomic(page, KM_USER0);
-                memset(kaddr + (first_hole << blkbits), 0,
-                                PAGE_CACHE_SIZE - (first_hole << blkbits));
-                flush_dcache_page(page);
-                kunmap_atomic(kaddr, KM_USER0);
+                zero_user_page(page, first_hole << blkbits,
+                                PAGE_CACHE_SIZE - (first_hole << blkbits),
+                                KM_USER0);
                 if (first_hole == 0) {
                         SetPageUptodate(page);
                         unlock_page(page);
@@ -576,14 +574,11 @@ page_is_mapped:
                  * written out to the file."
                  */
                 unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
-                char *kaddr;
 
                 if (page->index > end_index || !offset)
                         goto confused;
-                kaddr = kmap_atomic(page, KM_USER0);
-                memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
-                flush_dcache_page(page);
-                kunmap_atomic(kaddr, KM_USER0);
+                zero_user_page(page, offset, PAGE_CACHE_SIZE - offset,
+                                KM_USER0);
         }
 
         /*
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
diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
index cbb335813ec0..1b49dab9b25d 100644
--- a/mm/filemap_xip.c
+++ b/mm/filemap_xip.c
@@ -434,7 +434,6 @@ xip_truncate_page(struct address_space *mapping, loff_t from)
         unsigned blocksize;
         unsigned length;
         struct page *page;
-        void *kaddr;
 
         BUG_ON(!mapping->a_ops->get_xip_page);
 
@@ -458,11 +457,7 @@ xip_truncate_page(struct address_space *mapping, loff_t from)
                 else
                         return PTR_ERR(page);
         }
-        kaddr = kmap_atomic(page, KM_USER0);
-        memset(kaddr + offset, 0, length);
-        kunmap_atomic(kaddr, KM_USER0);
-
-        flush_dcache_page(page);
+        zero_user_page(page, offset, length, KM_USER0);
         return 0;
 }
 EXPORT_SYMBOL_GPL(xip_truncate_page);
diff --git a/mm/truncate.c b/mm/truncate.c
index 0f4b6d18ab0e..4fbe1a2da5fb 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -12,6 +12,7 @@
 #include <linux/swap.h>
 #include <linux/module.h>
 #include <linux/pagemap.h>
+#include <linux/highmem.h>
 #include <linux/pagevec.h>
 #include <linux/task_io_accounting_ops.h>
 #include <linux/buffer_head.h>  /* grr. try_to_release_page,
@@ -46,7 +47,7 @@ void do_invalidatepage(struct page *page, unsigned long offset)
 
 static inline void truncate_partial_page(struct page *page, unsigned partial)
 {
-        memclear_highpage_flush(page, partial, PAGE_CACHE_SIZE-partial);
+        zero_user_page(page, partial, PAGE_CACHE_SIZE - partial, KM_USER0);
         if (PagePrivate(page))
                 do_invalidatepage(page, partial);
 }