ext4: add EXT4_IOC_ALLOC_DA_BLKS ioctl
Add an ioctl which forces all of the delay allocated blocks to be
allocated. This also provides a function ext4_alloc_da_blocks() which
will be used by the following commits to force files to be fully
allocated to preserve application-expected ext3 behaviour.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 24d0f9d..8dd3d5d 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2837,6 +2837,48 @@
return;
}
+/*
+ * Force all delayed allocation blocks to be allocated for a given inode.
+ */
+int ext4_alloc_da_blocks(struct inode *inode)
+{
+ if (!EXT4_I(inode)->i_reserved_data_blocks &&
+ !EXT4_I(inode)->i_reserved_meta_blocks)
+ return 0;
+
+ /*
+ * We do something simple for now. The filemap_flush() will
+ * also start triggering a write of the data blocks, which is
+ * not strictly speaking necessary (and for users of
+ * laptop_mode, not even desirable). However, to do otherwise
+ * would require replicating code paths in:
+ *
+ * ext4_da_writepages() ->
+ * write_cache_pages() ---> (via passed in callback function)
+ * __mpage_da_writepage() -->
+ * mpage_add_bh_to_extent()
+ * mpage_da_map_blocks()
+ *
+ * The problem is that write_cache_pages(), located in
+ * mm/page-writeback.c, marks pages clean in preparation for
+ * doing I/O, which is not desirable if we're not planning on
+ * doing I/O at all.
+ *
+ * We could call write_cache_pages(), and then redirty all of
+ * the pages by calling redirty_page_for_writeback() but that
+ * would be ugly in the extreme. So instead we would need to
+ * replicate parts of the code in the above functions,
+ * simplifying them becuase we wouldn't actually intend to
+ * write out the pages, but rather only collect contiguous
+ * logical block extents, call the multi-block allocator, and
+ * then update the buffer heads with the block allocations.
+ *
+ * For now, though, we'll cheat by calling filemap_flush(),
+ * which will map the blocks, and start the I/O, but not
+ * actually wait for the I/O to complete.
+ */
+ return filemap_flush(inode->i_mapping);
+}
/*
* bmap() is special. It gets used by applications such as lilo and by