f2fs: support atomic writes

This patch introduces a very limited functionality for atomic write support.
In order to support atomic write, this patch adds two ioctls:
 o F2FS_IOC_START_ATOMIC_WRITE
 o F2FS_IOC_COMMIT_ATOMIC_WRITE

The database engine should be aware of the following sequence.
1. open
 -> ioctl(F2FS_IOC_START_ATOMIC_WRITE);
2. writes
  : all the written data will be treated as atomic pages.
3. commit
 -> ioctl(F2FS_IOC_COMMIT_ATOMIC_WRITE);
  : this flushes all the data blocks to the disk, which will be shown all or
  nothing by f2fs recovery procedure.
4. repeat to #2.

The IO pattens should be:

  ,- START_ATOMIC_WRITE                  ,- COMMIT_ATOMIC_WRITE
 CP | D D D D D D | FSYNC | D D D D | FSYNC ...
                      `- COMMIT_ATOMIC_WRITE

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index afb73627a8ec..2495bec1c621 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -175,6 +175,11 @@ struct segment_allocation {
 	void (*allocate_segment)(struct f2fs_sb_info *, int, bool);
 };
 
+struct inmem_pages {
+	struct list_head list;
+	struct page *page;
+};
+
 struct sit_info {
 	const struct segment_allocation *s_ops;
 
@@ -504,7 +509,7 @@ static inline bool need_inplace_update(struct inode *inode)
 	unsigned int policy = SM_I(sbi)->ipu_policy;
 
 	/* IPU can be done only for the user data */
-	if (S_ISDIR(inode->i_mode))
+	if (S_ISDIR(inode->i_mode) || f2fs_is_atomic_file(inode))
 		return false;
 
 	if (policy & (0x1 << F2FS_IPU_FORCE))