On Thu, 13 May 2010 16:09:55 +1000, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > On Thu, May 13, 2010 at 09:44:22AM +1000, Neil Brown wrote: > > On Wed, 12 May 2010 21:20:39 +0530 > > "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote: > > > > > + filp->f_flags |= O_NOATIME; > > > + filp->f_mode |= FMODE_NOCMTIME; > > > + } > > > > I think you need a comment here explaining the rational for these setting. > > If you've never seen how applications use the XFS handle interface > in conjunction with other XFS functionality, then I guess if would > seem like bad voodoo. > > > Why is O_NOATIME important IFREG but not for IFDIR? > > No application has ever required directory access or modification > via the handle interface to be invisible to the rest of the system. > > > Why is it not sufficient to honour O_NOATIME that is passed in. > > Because the XFS handle library is cross platform and predates > O_NOATIME on linux. Hence the library it has never set that flag and > always relied on the kernel implementation of the API to ensure > atime was never updated on fds derived from handles.. > > > How can you ever justify setting FMODE_NOCMTIME ? > > Quite easily. ;) > > The XFS handle interface was designed specifically to allow > applications to execute silent/invisible movement of data in, out > and around the filesystem without leaving user visible traces in > file metadata. This enables backup or filesysetm utilities that > operate on active filesystems need to be able to access or modify > inodes and data without affecting running applications. It's a > feature of the handle interface, and used by xfs_dump, xfs_fsr, > SGI's HSM, etc to do stuff that isn't otherwise possible. > > FWIW, if you are curious, here's the initial commit of the XFS > handle code into Irix tree from 3 Sep 1994, showing that the initial > XFS open_by_handle() implementation sets the FINVIS flag to trigger > invisible IO semantics: > > http://oss.sgi.com/cgi-bin/gitweb.cgi?p=archive/xfs-import.git;a=commitdiff;h=575b66fae833429a51fcadb204d45521c2dfc26f Thanks for sharing this. I haven't looked at the details you mentioned here. > > > I guess you are just copying from xfs code, but it still needs justification. > > "They are intended for use by a limited set of system > utilities such as backup programs." > > - open_by_handle(3) man page > Should we retain all the above behaviour in the new syscall ?. Or just do what a normal open(2) call does ? -aneesh -- 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
