On 1/8/17 8:11 PM, Qu Wenruo wrote: > > > At 01/08/2017 09:16 PM, Goldwyn Rodrigues wrote: >> >> 1. Motivation >> While fixing user space tools for btrfs-progs, I found a couple of bugs >> which are already solved in kernel space but were not ported to user >> space. User space is a little ignored when it comes to fixing bugs in >> the core functionality. XFS developers have already performed this and >> the userspace and kernel code walks in lockstep for libxfs. > > Personally speaking, I'm not a fan of re-using kernel code in btrfs-progs.
But it already does re-use kernel code, it's just that the re-use is extremely stale, with unfixed bugs in both directions as a result (at least last time I looked.) > In fact, in btrfs-progs, we don't need a lot of kernel facilities, > like page/VFS/lock(btrfs-progs works in single thread under most > case). > > And that should make btrfs-progs easier to maintain. But as Goldwyn already pointed out, many bugs have gone un-fixed in userspace, in code which was forked long ago from kernelspace. For things like locking it's trivial to define that away. xfsprogs does i.e. - /* miscellaneous kernel routines not in user space */ #define down_read(a) ((void) 0) #define up_read(a) ((void) 0) #define spin_lock_init(a) ((void) 0) #define spin_lock(a) ((void) 0) #define spin_unlock(a) ((void) 0) #define likely(x) (x) #define unlikely(x) (x) #define rcu_read_lock() ((void) 0) #define rcu_read_unlock() ((void) 0) #define WARN_ON_ONCE(expr) ((void) 0) > Furthermore, there are cases while kernel is doing things wrong while > btrfs-progs does it right. All the more reason to sync it up, fixes should always be in both places, right? I had looked at this a few years ago, and started trying to sync things up, but got daunted and busy and never completed anything. :( I sent a few fixups back in April 2013 to get things /slightly/ closer. The libxfs sync in xfs has borne fruit; I'm of the opinion that similar work would help btrfs too, though it can be a long road. (e2fsprogs has gone the other way, and has a completely separate re-implementation in userspace; it works, I guess, but I have to say that I really like the code commonality in xfs.) Thanks, -Eric -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
