[PATCH 2/6] f2fs: do not expose unwritten blocks to user by DIO

[Jaegeuk Kim]

DIO preallocates physical blocks before writing data, but if an error occurrs
or power-cut happens, we can see block contents from the disk. This patch tries
to fix it by 1) turning to buffered writes for DIO into holes, 2) truncating
unwritten blocks from error or power-cut.

Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
---
 fs/f2fs/data.c |  5 ++++-
 fs/f2fs/f2fs.h |  5 +++++
 fs/f2fs/file.c | 24 +++++++++++++++++++++++-
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 3b27fb7daa8b..7ac1a39fcad2 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1543,8 +1543,11 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map,
 					flag != F2FS_GET_BLOCK_DIO);
 				err = __allocate_data_block(&dn,
 							map->m_seg_type);
-				if (!err)
+				if (!err) {
+					if (flag == F2FS_GET_BLOCK_PRE_DIO)
+						file_need_truncate(inode);
 					set_inode_flag(inode, FI_APPEND_WRITE);
+				}
 			}
 			if (err)
 				goto sync_out;
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index be871a79c634..14bea669f87e 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -654,6 +654,7 @@ enum {
 #define FADVISE_KEEP_SIZE_BIT	0x10
 #define FADVISE_HOT_BIT		0x20
 #define FADVISE_VERITY_BIT	0x40
+#define FADVISE_TRUNC_BIT	0x80
 
 #define FADVISE_MODIFIABLE_BITS	(FADVISE_COLD_BIT | FADVISE_HOT_BIT)
 
@@ -681,6 +682,10 @@ enum {
 #define file_is_verity(inode)	is_file(inode, FADVISE_VERITY_BIT)
 #define file_set_verity(inode)	set_file(inode, FADVISE_VERITY_BIT)
 
+#define file_should_truncate(inode)	is_file(inode, FADVISE_TRUNC_BIT)
+#define file_need_truncate(inode)	set_file(inode, FADVISE_TRUNC_BIT)
+#define file_dont_truncate(inode)	clear_file(inode, FADVISE_TRUNC_BIT)
+
 #define DEF_DIR_LEVEL		0
 
 enum {
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 4bf77a5bf998..ec8de0662437 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -960,10 +960,21 @@ int f2fs_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 		down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
 		filemap_invalidate_lock(inode->i_mapping);
 
+		/*
+		 * Truncate stale preallocated blocks used by the previous DIO.
+		 */
+		if (file_should_truncate(inode)) {
+			err = f2fs_truncate(inode);
+			if (err)
+				goto out_unlock;
+			file_dont_truncate(inode);
+		}
+
 		truncate_setsize(inode, attr->ia_size);
 
 		if (attr->ia_size <= old_size)
 			err = f2fs_truncate(inode);
+out_unlock:
 		/*
 		 * do not trim all blocks after i_size if target size is
 		 * larger than i_size.
@@ -4257,6 +4268,13 @@ static int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *iter)
 	/* If it will be an out-of-place direct write, don't bother. */
 	if (dio && f2fs_lfs_mode(sbi))
 		return 0;
+	/*
+	 * Don't preallocate holes aligned to DIO_SKIP_HOLES which turns into
+	 * buffered IO, if DIO meets any holes.
+	 */
+	if (dio && i_size_read(inode) &&
+		(F2FS_BYTES_TO_BLK(pos) < F2FS_BLK_ALIGN(i_size_read(inode))))
+		return 0;
 
 	/* No-wait I/O can't allocate blocks. */
 	if (iocb->ki_flags & IOCB_NOWAIT)
@@ -4366,10 +4384,14 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		if (preallocated > 0 && i_size_read(inode) < target_size) {
 			down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
 			filemap_invalidate_lock(inode->i_mapping);
-			f2fs_truncate(inode);
+			if (!f2fs_truncate(inode))
+				file_dont_truncate(inode);
 			filemap_invalidate_unlock(inode->i_mapping);
 			up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
+		} else {
+			file_dont_truncate(inode);
 		}
+
 		clear_inode_flag(inode, FI_PREALLOCATED_ALL);
 
 		if (ret > 0)
-- 
2.34.0.rc1.387.gb447b232ab-goog