On Tue, Jan 07, 2014 at 07:59:15PM +0000, Chris Mason wrote: > On Tue, 2014-01-07 at 11:43 -0800, Darrick J. Wong wrote: > > On Tue, Jan 07, 2014 at 12:04:30PM -0500, Theodore Ts'o wrote: > > > On Tue, Jan 07, 2014 at 07:49:35AM -0800, Christoph Hellwig wrote: > > > > On Tue, Jan 07, 2014 at 01:48:31PM +0100, Jan Kara wrote: > > > > > I have to say I'm not thrilled by the idea of juggling strings in > > > > > userspace and in kernel to set a flag for an inode... > > > > > > > > Nevermind the massive amounts of code that sit in the filesystem. > > > > > > The reason for this patch was to address what Dave Chinner has called > > > "a shitty interface"[1]. Using bitfields that need to be coordinated > > > across file systems, when sometimes a bit assignment is validly a fs > > > specific thing, and then later becomes something that gets shared > > > across file systems. > > > > > > [1] http://thread.gmane.org/gmane.linux.file-systems/80164/focus=80396 > > > > > > If we don't go about it this way, there are alternatives: we could > > > create new ioctls (or a new syscall) as we start running out of bits > > > used by FS_IOC_[GS]ETFLAGS. We can create new ioctls for bits which > > > are intended for fs-specific flags, which then later get promoted to > > > the new syscall when some functionality starts to get shared accross > > > other file systems (probably with a different bit assignment). This > > > is certainly less code, but it does mean more complexity outside of > > > the code when we try to coordinate new functionality across file > > > systems. > > > > I had thought of indexed inode flags as an alternative to the xattr/string > > parsing thing. Feature flags make their first appearance as part of a per-FS > > flag-space and are migrated to the common flag-space when there is demand. > > It would also avoid the need for each fs to create its own flag ioctl. > > > > On the other hand, someone suggested I try remaking IOC_[GS]ETFLAG as an xattr, > > so off I went. :) > > > > At least in btrfs xattrs are more expensive than something right in the > inode. We can cache it when we load the inode (it'll be right next to > the inode most of the time) but for performance critical things I do > like the good old fashioned flags. Just to clarify -- I wasn't proposing any on-disk changes for any filesystems, merely creating virtual xattrs that wrap the inode flags. > It's also possible to turn xattrs off, so we have to deal with > filesystems that are mounted with them off and then back on again. I > can't think of huge problems from that right now, just something to be > aware of. Just to satisfy my curiosity: are xattrs always separate objects in btrfs? --D > > -chris > > -- > 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 -- 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
