f2fs: allocate blocks for pinned file

This patch allows fallocate to allocate physical blocks for pinned file.
Reviewed-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

Documentation/filesystems/f2fs.txt

@@ -804,3 +804,28 @@ WRITE_LIFE_NOT_SET    WARM_DATA                WRITE_LIFE_NOT_SET
 WRITE_LIFE_NONE       "                        WRITE_LIFE_NONE
 WRITE_LIFE_MEDIUM     "                        WRITE_LIFE_MEDIUM
 WRITE_LIFE_LONG       "                        WRITE_LIFE_LONG
+
+Fallocate(2) Policy
+-------------------
+
+The default policy follows the below posix rule.
+
+Allocating disk space
+    The default operation (i.e., mode is zero) of fallocate() allocates
+    the disk space within the range specified by offset and len.  The
+    file size (as reported by stat(2)) will be changed if offset+len is
+    greater than the file size.  Any subregion within the range specified
+    by offset and len that did not contain data before the call will be
+    initialized to zero.  This default behavior closely resembles the
+    behavior of the posix_fallocate(3) library function, and is intended
+    as a method of optimally implementing that function.
+
+However, once F2FS receives ioctl(fd, F2FS_IOC_SET_PIN_FILE) in prior to
+fallocate(fd, DEFAULT_MODE), it allocates on-disk blocks addressess having
+zero or random data, which is useful to the below scenario where:
+ 1. create(fd)
+ 2. ioctl(fd, F2FS_IOC_SET_PIN_FILE)
+ 3. fallocate(fd, 0, 0, size)
+ 4. address = fibmap(fd, offset)
+ 5. open(blkdev)
+ 6. write(blkdev, address)

fs/f2fs/file.c

@@ -1528,7 +1528,12 @@ static int expand_inode_data(struct inode *inode, loff_t offset,
 	if (off_end)
 		map.m_len++;
 
-	err = f2fs_map_blocks(inode, &map, 1, F2FS_GET_BLOCK_PRE_AIO);
+	if (f2fs_is_pinned_file(inode))
+		map.m_seg_type = CURSEG_COLD_DATA;
+
+	err = f2fs_map_blocks(inode, &map, 1, (f2fs_is_pinned_file(inode) ?
+						F2FS_GET_BLOCK_PRE_DIO :
+						F2FS_GET_BLOCK_PRE_AIO));
 	if (err) {
 		pgoff_t last_off;