On Fri, Jan 14, 2011 at 3:18 AM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > On Thu, 13 Jan 2011, Miklos Szeredi wrote: >> On Sat, 8 Jan 2011, Nick Piggin wrote: >> > The vfs-scale branch is now upstream. If you haven't >> > looked yet, your filesystem is likely to have been >> > touched, so check it out. >> > >> > Also look at Documentation/filesystems/porting and >> > path-lookup.txt. >> > >> > The dcache_lock stuff should have been all done for you >> > (for in-tree filesystems, I can help out of tree fses with >> > conversions there if you ping me offline). >> > >> > The rcu-walk stuff can be more tricky for your filesystem >> > to take advantage of. >> > >> > If you supply a .d_revalidate, .permission, or .check_acl, >> > then path walking is going to be slow and unscalable for >> > you. >> > >> > Out of tree filesystems: you _have_ to at least add a line >> > of code to the above functions in order to specify that >> > you don't want to participate in rcu-walk. >> > >> > Otherwise, you don't have to care about rcu-walk if you >> > have a legacy or special filesystem like configfs then I'd >> > advise against anything fancy. But if you have a >> > userbase and you expect them to actually do any path >> > lookups into your filesystem, please take a look. >> >> One other thing: I know ECHILD is safe since no sane filesystem will >> return it in its permission or revalidate callbacks, and even if it >> does that's just a loss of optimization. > > And it's not entirely safe either. A fuse filesystem returning ECHILD > would make nameidata_dentry_drop_rcu() to BUG. So some sort of errno > filter is necessary in the fuse kernel module. Surely you'd need some filtering anyway? I don't think any function involving path lookup could sanely return -ECHILD. That said, it probably is a good idea to have a new errno. -- 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
