• Chao Yu's avatar
    f2fs: support revoking atomic written pages · 28bc106b
    Chao Yu authored
    
    
    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: default avatarChao Yu <chao2.yu@samsung.com>
    Signed-off-by: default avatarJaegeuk Kim <jaegeuk@kernel.org>
    28bc106b
file.c 44.7 KB