1 files changed, 49 insertions, 2 deletions

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index a10dc7742aec..1c81509f5bd9 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -93,9 +93,13 @@ static ssize_t
 ext4_file_dio_write(struct kiocb *iocb, const struct iovec *iov,
                     unsigned long nr_segs, loff_t pos)
 {
-        struct inode *inode = iocb->ki_filp->f_path.dentry->d_inode;
+        struct file *file = iocb->ki_filp;
+        struct inode *inode = file->f_mapping->host;
+        struct blk_plug plug;
         int unaligned_aio = 0;
         ssize_t ret;
+        int overwrite = 0;
+        size_t length = iov_length(iov, nr_segs);
 
         if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) &&
             !is_sync_kiocb(iocb))
@@ -115,7 +119,50 @@ ext4_file_dio_write(struct kiocb *iocb, const struct iovec *iov,
                 ext4_aiodio_wait(inode);
         }
 
-        ret = generic_file_aio_write(iocb, iov, nr_segs, pos);
+        BUG_ON(iocb->ki_pos != pos);
+
+        mutex_lock(&inode->i_mutex);
+        blk_start_plug(&plug);
+
+        iocb->private = &overwrite;
+
+        /* check whether we do a DIO overwrite or not */
+        if (ext4_should_dioread_nolock(inode) && !unaligned_aio &&
+            !file->f_mapping->nrpages && pos + length <= i_size_read(inode)) {
+                struct ext4_map_blocks map;
+                unsigned int blkbits = inode->i_blkbits;
+                int err, len;
+
+                map.m_lblk = pos >> blkbits;
+                map.m_len = (EXT4_BLOCK_ALIGN(pos + length, blkbits) >> blkbits)
+                        - map.m_lblk;
+                len = map.m_len;
+
+                err = ext4_map_blocks(NULL, inode, &map, 0);
+                /*
+                 * 'err==len' means that all of blocks has been preallocated no
+                 * matter they are initialized or not.  For excluding
+                 * uninitialized extents, we need to check m_flags.  There are
+                 * two conditions that indicate for initialized extents.
+                 * 1) If we hit extent cache, EXT4_MAP_MAPPED flag is returned;
+                 * 2) If we do a real lookup, non-flags are returned.
+                 * So we should check these two conditions.
+                 */
+                if (err == len && (map.m_flags & EXT4_MAP_MAPPED))
+                        overwrite = 1;
+        }
+
+        ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
+        mutex_unlock(&inode->i_mutex);
+
+        if (ret > 0 || ret == -EIOCBQUEUED) {
+                ssize_t err;
+
+                err = generic_write_sync(file, pos, ret);
+                if (err < 0 && ret > 0)
+                        ret = err;
+        }
+        blk_finish_plug(&plug);
 
         if (unaligned_aio)
                 mutex_unlock(ext4_aio_mutex(inode));