[PATCH v4] UDF: Add support for O_DIRECT

[Ian Abbott <abbotti@mev.co.uk>]

Add support for the O_DIRECT flag.  There are two cases to deal with:

1. Small files stored in the ICB (inode control block?): just return 0
from the new udf_adinicb_direct_IO() handler to fall back to buffered
I/O.

2. Larger files, not stored in the ICB: nothing special here.  Just call
blockdev_direct_IO() from our new udf_direct_IO() handler and tidy up
any blocks instantiated outside i_size on error.  This is pretty
standard.  Factor error handling code out of udf_write_begin() into new
function udf_write_failed() so it can also be called by udf_direct_IO().

Also change the whitespace in udf_aops to make it a bit neater.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
---
v2: Rework error handling in udf_direct_IO to avoid calling deprecated
    vmtruncate().
v3: Rebased to next-20120904.
v4: Removed special handling in udf_adinicb_writepage() as that turned
    out to be a bug in the handling of buffered writes for files in ICB,
    fixed by Jan Kara's patch "udf: Fix data corruption for files in
    ICB", dated 2012-09-05.  I've tested it with that patch and it seems
    to work without corrupting file data in the ICB.
---
 fs/udf/file.c  |  9 +++++++++
 fs/udf/inode.c | 52 ++++++++++++++++++++++++++++++++++++----------------
 2 files changed, 45 insertions(+), 16 deletions(-)

diff --git a/fs/udf/file.c b/fs/udf/file.c
index d1c6093..77b5953 100644
--- a/fs/udf/file.c
+++ b/fs/udf/file.c
@@ -118,11 +118,20 @@ static int udf_adinicb_write_end(struct file *file,
 	return simple_write_end(file, mapping, pos, len, copied, page, fsdata);
 }
 
+static ssize_t udf_adinicb_direct_IO(int rw, struct kiocb *iocb,
+				     const struct iovec *iov,
+				     loff_t offset, unsigned long nr_segs)
+{
+	/* Fallback to buffered I/O. */
+	return 0;
+}
+
 const struct address_space_operations udf_adinicb_aops = {
 	.readpage	= udf_adinicb_readpage,
 	.writepage	= udf_adinicb_writepage,
 	.write_begin	= udf_adinicb_write_begin,
 	.write_end	= udf_adinicb_write_end,
+	.direct_IO	= udf_adinicb_direct_IO,
 };
 
 static ssize_t udf_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index 1a0588e..b905448 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -95,6 +95,22 @@ void udf_evict_inode(struct inode *inode)
 	}
 }
 
+static void udf_write_failed(struct address_space *mapping, loff_t to)
+{
+	struct inode *inode = mapping->host;
+	struct udf_inode_info *iinfo = UDF_I(inode);
+	loff_t isize = inode->i_size;
+
+	if (to > isize) {
+		truncate_pagecache(inode, to, isize);
+		if (iinfo->i_alloc_type != ICBTAG_FLAG_AD_IN_ICB) {
+			down_write(&iinfo->i_data_sem);
+			udf_truncate_extents(inode);
+			up_write(&iinfo->i_data_sem);
+		}
+	}
+}
+
 static int udf_writepage(struct page *page, struct writeback_control *wbc)
 {
 	return block_write_full_page(page, udf_get_block, wbc);
@@ -124,21 +140,24 @@ static int udf_write_begin(struct file *file, struct address_space *mapping,
 	int ret;
 
 	ret = block_write_begin(mapping, pos, len, flags, pagep, udf_get_block);
-	if (unlikely(ret)) {
-		struct inode *inode = mapping->host;
-		struct udf_inode_info *iinfo = UDF_I(inode);
-		loff_t isize = inode->i_size;
-
-		if (pos + len > isize) {
-			truncate_pagecache(inode, pos + len, isize);
-			if (iinfo->i_alloc_type != ICBTAG_FLAG_AD_IN_ICB) {
-				down_write(&iinfo->i_data_sem);
-				udf_truncate_extents(inode);
-				up_write(&iinfo->i_data_sem);
-			}
-		}
-	}
+	if (unlikely(ret))
+		udf_write_failed(mapping, pos + len);
+	return ret;
+}
 
+static ssize_t udf_direct_IO(int rw, struct kiocb *iocb,
+			     const struct iovec *iov,
+			     loff_t offset, unsigned long nr_segs)
+{
+	struct file *file = iocb->ki_filp;
+	struct address_space *mapping = file->f_mapping;
+	struct inode *inode = mapping->host;
+	ssize_t ret;
+
+	ret = blockdev_direct_IO(rw, iocb, inode, iov, offset, nr_segs,
+				  udf_get_block);
+	if (unlikely(ret < 0 && (rw && WRITE)))
+		udf_write_failed(mapping, offset + iov_length(iov, nr_segs));
 	return ret;
 }
 
@@ -152,8 +171,9 @@ const struct address_space_operations udf_aops = {
 	.readpages	= udf_readpages,
 	.writepage	= udf_writepage,
 	.writepages	= udf_writepages,
-	.write_begin		= udf_write_begin,
-	.write_end		= generic_write_end,
+	.write_begin	= udf_write_begin,
+	.write_end	= generic_write_end,
+	.direct_IO	= udf_direct_IO,
 	.bmap		= udf_bmap,
 };
 
-- 
1.7.12