introduce __block_write_begin

Split up the block_write_begin implementation - __block_write_begin is a new
trivial wrapper for block_prepare_write that always takes an already
allocated page and can be either called from block_write_begin or filesystem
code that already has a page allocated.  Remove the handling of already
allocated pages from block_write_begin after switching all callers that
do it to __block_write_begin.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 26 insertions, 43 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index 14529ec759b9..c319c49da511 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1833,9 +1833,10 @@ void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
 }
 EXPORT_SYMBOL(page_zero_new_buffers);
 
-static int __block_prepare_write(struct inode *inode, struct page *page,
-                unsigned from, unsigned to, get_block_t *get_block)
+int block_prepare_write(struct page *page, unsigned from, unsigned to,
+                get_block_t *get_block)
 {
+        struct inode *inode = page->mapping->host;
         unsigned block_start, block_end;
         sector_t block;
         int err = 0;
@@ -1908,10 +1909,13 @@ static int __block_prepare_write(struct inode *inode, struct page *page,
                 if (!buffer_uptodate(*wait_bh))
                         err = -EIO;
         }
-        if (unlikely(err))
+        if (unlikely(err)) {
                 page_zero_new_buffers(page, from, to);
+                ClearPageUptodate(page);
+        }
         return err;
 }
+EXPORT_SYMBOL(block_prepare_write);
 
 static int __block_commit_write(struct inode *inode, struct page *page,
                 unsigned from, unsigned to)
@@ -1948,6 +1952,15 @@ static int __block_commit_write(struct inode *inode, struct page *page,
         return 0;
 }
 
+int __block_write_begin(struct page *page, loff_t pos, unsigned len,
+                get_block_t *get_block)
+{
+        unsigned start = pos & (PAGE_CACHE_SIZE - 1);
+
+        return block_prepare_write(page, start, start + len, get_block);
+}
+EXPORT_SYMBOL(__block_write_begin);
+
 /*
  * Filesystems implementing the new truncate sequence should use the
  * _newtrunc postfix variant which won't incorrectly call vmtruncate.
@@ -1958,41 +1971,22 @@ int block_write_begin_newtrunc(struct file *file, struct address_space *mapping,
                         struct page **pagep, void **fsdata,
                         get_block_t *get_block)
 {
-        struct inode *inode = mapping->host;
-        int status = 0;
+        pgoff_t index = pos >> PAGE_CACHE_SHIFT;
         struct page *page;
-        pgoff_t index;
-        unsigned start, end;
-        int ownpage = 0;
+        int status;
 
-        index = pos >> PAGE_CACHE_SHIFT;
-        start = pos & (PAGE_CACHE_SIZE - 1);
-        end = start + len;
-
-        page = *pagep;
-        if (page == NULL) {
-                ownpage = 1;
-                page = grab_cache_page_write_begin(mapping, index, flags);
-                if (!page) {
-                        status = -ENOMEM;
-                        goto out;
-                }
-                *pagep = page;
-        } else
-                BUG_ON(!PageLocked(page));
+        page = grab_cache_page_write_begin(mapping, index, flags);
+        if (!page)
+                return -ENOMEM;
 
-        status = __block_prepare_write(inode, page, start, end, get_block);
+        status = __block_write_begin(page, pos, len, get_block);
         if (unlikely(status)) {
-                ClearPageUptodate(page);
-
-                if (ownpage) {
-                        unlock_page(page);
-                        page_cache_release(page);
-                        *pagep = NULL;
-                }
+                unlock_page(page);
+                page_cache_release(page);
+                page = NULL;
         }
 
-out:
+        *pagep = page;
         return status;
 }
 EXPORT_SYMBOL(block_write_begin_newtrunc);
@@ -2379,17 +2373,6 @@ out:
 }
 EXPORT_SYMBOL(cont_write_begin);
 
-int block_prepare_write(struct page *page, unsigned from, unsigned to,
-                        get_block_t *get_block)
-{
-        struct inode *inode = page->mapping->host;
-        int err = __block_prepare_write(inode, page, from, to, get_block);
-        if (err)
-                ClearPageUptodate(page);
-        return err;
-}
-EXPORT_SYMBOL(block_prepare_write);
-
 int block_commit_write(struct page *page, unsigned from, unsigned to)
 {
         struct inode *inode = page->mapping->host;