linux-ext4 - [PATCH, RFC] ext4: add EXT4_IOC_ALLOC_DA

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Message-Id: <1235451952-2726-5-git-send-email-tytso@mit.edu>
Date:	Tue, 24 Feb 2009 00:05:50 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	linux-ext4@...r.kernel.org
Cc:	aneesh.kumar@...ux.vnet.ibm.com, Theodore Ts'o <tytso@....edu>
Subject: [PATCH, RFC] 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@....edu>
---
 fs/ext4/ext4.h  |    2 ++
 fs/ext4/inode.c |   42 ++++++++++++++++++++++++++++++++++++++++++
 fs/ext4/ioctl.c |   13 +++++++++++++
 3 files changed, 57 insertions(+), 0 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 9840cad..626bda7 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -316,6 +316,7 @@ struct ext4_new_group_data {
 #define EXT4_IOC_GROUP_EXTEND		_IOW('f', 7, unsigned long)
 #define EXT4_IOC_GROUP_ADD		_IOW('f', 8, struct ext4_new_group_input)
 #define EXT4_IOC_MIGRATE		_IO('f', 9)
+#define EXT4_IOC_ALLOC_DA_BLKS		_IO('f', 10)
  /* note ioctl 11 reserved for filesystem-independent FIEMAP ioctl */
 
 /*
@@ -1094,6 +1095,7 @@ extern int ext4_chunk_trans_blocks(struct inode *, int nrblocks);
 extern int ext4_block_truncate_page(handle_t *handle,
 		struct address_space *mapping, loff_t from);
 extern int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page);
+extern int ext4_alloc_da_blocks(struct inode *inode);
 
 /* ioctl.c */
 extern long ext4_ioctl(struct file *, unsigned int, unsigned long);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 1216fb9..c66af1c 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2807,6 +2807,48 @@ out:
 	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
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 22dd29f..0d59f5f 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -262,6 +262,19 @@ setversion_out:
 		return err;
 	}
 
+	case EXT4_IOC_ALLOC_DA_BLKS:
+	{
+		int err;
+		if (!is_owner_or_cap(inode))
+			return -EACCES;
+
+		err = mnt_want_write(filp->f_path.mnt);
+		if (err)
+			return err;
+		err = ext4_alloc_da_blocks(inode);
+		return err;
+	}
+
 	default:
 		return -ENOTTY;
 	}
-- 
1.5.6.3

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