On Thu, 2012-01-05 at 14:49 -0500, Mimi Zohar wrote: > On Thu, 2012-01-05 at 13:14 -0500, Christoph Hellwig wrote: > > On Thu, Jan 05, 2012 at 03:53:54PM +1100, Dave Chinner wrote: > > > That's seems like a rather unreliable way of detecting that a file > > > has changed to me. I mean, only ext4 uses inode_inc_version() when > > > it internally dirties an inode, and only ext4 sets the MS_I_VERSION > > > so that inode_inc_version is only called for ext4 inodes when > > > timestamps change. > > > > And even ext4 only does it when using the non-default "i_version" > > mount option. > > > > > Hence just adding an increment to the truncate case doesn't seem to > > > be sufficient to me. e.g. what about the equivalent case of having a > > > hole punched in the file via fallocate? The file has definitely > > > changed, but i_version won't change.... > > > > > > Perhaps bumping i_version in __mark_inode_dirty() might be the best > > > way to capture all changes (other than timestamp updates) to any > > > inode regardless of the filesystem type? > > > > It has the same problem as the timestamp updates doing that right now - > > the fs can't do locking around it, and it can't return errors. That's > > something affecting at least btrfs, xfs and IIRC ubifs, and probably > > the cluster filesystems as well. The right answer is to replace the > > timestmap updates which are the only places doing that with a method > > as Josef had planned to do, and then we can include the i_version > > updates in there. > > > > That assumes we figure out a coherent way to do it - except for the > > conditional abuse in file_updates_times it's currently entirely under > > fs control. So the best way to fix it would be to: > > > > - move the fs-private use into those filesystems actually using it. > > Note that a lot less actually check for it rather than just updating > > it based on some cargo cult, and most only do so for directories. > > - figure a why what exact change count semantics NFS (and IMA) want > > and find a way to implement them so that the fs can tell the callers > > that they don't exist. > > > > Btw, does IMA care about these beeing persistent? > > By 'persistent' I assume you mean across boots. IMA (and IMA-appraisal) > measure and appraise files the first time they're accessed/executed. So > no, it does not need to be persistent. IMA/IMA-appraisal just need some > way to detect file change in order to know whether the file needs to be > re-measured/appraised on subsequent access. One other IMA requirement would be the ability to detect if a file mmapped executable, after the point that it has been locked from modification, has changed since the last time measured/appraised. The concern here, in particular, is the ability to detect file change while holding the mmap_sem. thanks, Mimi -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
