f2fs: support revoking atomic written pages

f2fs support atomic write with following semantics:
1. open db file
2. ioctl start atomic write
3. (write db file) * n
4. ioctl commit atomic write
5. close db file

With this flow we can avoid file becoming corrupted when abnormal power
cut, because we hold data of transaction in referenced pages linked in
inmem_pages list of inode, but without setting them dirty, so these data
won't be persisted unless we commit them in step 4.

But we should still hold journal db file in memory by using volatile
write, because our semantics of 'atomic write support' is incomplete, in
step 4, we could fail to submit all dirty data of transaction, once
partial dirty data was committed in storage, then after a checkpoint &
abnormal power-cut, db file will be corrupted forever.

So this patch tries to improve atomic write flow by adding a revoking flow,
once inner error occurs in committing, this gives another chance to try to
revoke these partial submitted data of current transaction, it makes
committing operation more like aotmical one.

If we're not lucky, once revoking operation was failed, EAGAIN will be
reported to user for suggesting doing the recovery with held journal file,
or retrying current transaction again.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index d8caf0c86593..0d2b1ba9660e 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -686,6 +686,7 @@ enum page_type {
         META_FLUSH,
         INMEM,          /* the below types are used by tracepoints only. */
         INMEM_DROP,
+        INMEM_REVOKE,
         IPU,
         OPU,
 };
@@ -695,6 +696,7 @@ struct f2fs_io_info {
         enum page_type type;    /* contains DATA/NODE/META/META_FLUSH */
         int rw;                 /* contains R/RS/W/WS with REQ_META/REQ_PRIO */
         block_t blk_addr;       /* block address to be written */
+        block_t old_blkaddr;    /* old block address before Cow */
         struct page *page;      /* page to be written */
         struct page *encrypted_page;    /* encrypted page */
 };
@@ -1853,7 +1855,7 @@ void write_node_page(unsigned int, struct f2fs_io_info *);
 void write_data_page(struct dnode_of_data *, struct f2fs_io_info *);
 void rewrite_data_page(struct f2fs_io_info *);
 void f2fs_replace_block(struct f2fs_sb_info *, struct dnode_of_data *,
-                                block_t, block_t, unsigned char, bool);
+                                block_t, block_t, unsigned char, bool, bool);
 void allocate_data_block(struct f2fs_sb_info *, struct page *,
                 block_t, block_t *, struct f2fs_summary *, int);
 void f2fs_wait_on_page_writeback(struct page *, enum page_type, bool);