On Tue, Jun 26, 2007 at 12:14:00PM -0400, Andreas Dilger wrote: > On Jun 26, 2007 17:37 +0530, Amit K. Arora wrote: > > Hmm.. I am thinking of a scenario when the file system supports some > > individual flags, but does not support a particular combination of them. > > Just for example sake, assume we have FA_ZERO_SPACE mode also. Now, if a > > file system supports FA_ZERO_SPACE, FA_ALLOCATE, FA_DEALLOCATE and > > FA_RESV_SPACE; and no other mode (i.e. FA_UNRESV_SPACE is not supported > > for some reason). This means that although we support FA_FL_DEALLOC, > > FA_FL_KEEP_SIZE and FA_FL_DEL_DATA flags, but we do not support the > > combination of all these flags (which is nothing but FA_UNRESV_SPACE). > > That is up to the filesystem to determine then. I just thought it should > be clear to return an error for flags (or as you say combinations thereof) > that the filesystem doesn't understand. > > That said, I'd think in most cases the flags are orthogonal, so if you > support some combination of the flags (e.g. FA_FL_DEL_DATA, FA_FL_DEALLOC) > then you will also support other combinations of those flags just from > the way it is coded. Ok. > > > I also thought another proposed flag was to determine whether mtime (and > > > maybe ctime) is changed when doing prealloc/dealloc space? Default should > > > probably be to change mtime/ctime, and have FA_FL_NO_MTIME. Someone else > > > should decide if we want to allow changing the file w/o changing ctime, if > > > that is required even though the file is not visibly changing. Maybe the > > > ctime update should be implicit if the size or mtime are changing? > > > > Is it really required ? I mean, why should we allow users not to update > > ctime/mtime even if the file metadata/data gets updated ? It sounds > > a bit "unnatural" to me. > > Is there any application scenario in your mind, when you suggest of > > giving this flexibility to userspace ? > > One reason is that XFS does NOT update the mtime/ctime when doing the > XFS_IOC_* allocation ioctls. Hmm.. I personally will call it a bug in XFS code then. :) > > I think, modifying ctime/mtime should be dependent on the other flags. > > E.g., if we do not zero out data blocks on allocation/deallocation, > > update only ctime. Otherwise, update ctime and mtime both. > > I'm only being the advocate for requirements David Chinner has put > forward due to existing behaviour in XFS. This is one of the reasons > why I think the "flags" mechanism we now have - we can encode the > various different behaviours in any way we want and leave it to the > caller. I understand. May be we can confirm once more with David Chinner if this is really required. Will it really be a compatibility issue if new XFS preallocations (ie. via fallocate) update mtime/ctime ? Will old applications really get affected ? If yes, then it might be worth implementing - even though I personally don't like it. David, can you please confirm ? Thanks! -- Regards, Amit Arora - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
