> > > > > + err = jbd2_journal_flush(EXT4_SB(sb)->s_journal, > > > > > > Huh. So we don't flush the filesystem at all, just the journal? I > > > don't see anything in the documentation saying that syncfs() is a > > > prerequisite. > > This is just for the journal, good point, I'll update the documentation. It just occurred to me this morning that we need to ensure that a *full* commit happens before IOC_CHECKPOINT and not a *fast* commit. Fast commits cannot be checkpointed, they rely on full commits for checkpoint operation. So, if a syncfs call results in a fast commit, the following sequence of events will happen: * Ext4 writes fast commit information in fast commit area * When user calls EXT4_IOC_CHECKPOINT, the checkpoint operation would result in checkpointing everything in the main journal, except things written in fast commit area * During the discard phase of EXT4_IOC_CHECKPOINT, fast commit area will be discarded and thus we'll lose the log updates present in the fast commit area However, this isn't a problem today. Syncfs doesn't result in a fast commit but results in a full commit. But, that can change at some point in the future. So, unless we can either come up with syncfs() variant that can induce a full commit (which would be a little ugly - I don't think the user needs to know what kind of journal commit file system is doing) or add checkpointing support in fast commits, we should just do a full commit from the IOCTL code. - Harshad
