On Sat, Mar 30, 2013 at 8:52 PM, Myklebust, Trond <Trond.Myklebust@xxxxxxxxxx> wrote: > On Sat, 2013-03-30 at 19:53 -0700, Andreas Dilger wrote: >> On 2013-03-30, at 16:21, Ric Wheeler <rwheeler@xxxxxxxxxx> wrote: >> >> > On 03/30/2013 05:57 PM, Myklebust, Trond wrote: >> >> On Mar 30, 2013, at 5:45 PM, Pavel Machek <pavel@xxxxxx> >> >> wrote: >> >> >> >>> On Sat 2013-03-30 13:08:39, Andreas Dilger wrote: >> >>>> On 2013-03-30, at 12:49 PM, Pavel Machek wrote: >> >>>>> Hmm, really? AFAICT it would be simple to provide an >> >>>>> open_deleted_file("directory") syscall. You'd open_deleted_file(), >> >>>>> copy source file into it, then fsync(), then link it into filesystem. >> >>>>> >> >>>>> That should have atomicity properties reflected. >> >>>> Actually, the open_deleted_file() syscall is quite useful for many >> >>>> different things all by itself. Lots of applications need to create >> >>>> temporary files that are unlinked at application failure (without a >> >>>> race if app crashes after creating the file, but before unlinking). >> >>>> It also avoids exposing temporary files into the namespace if other >> >>>> applications are accessing the directory. >> >>> Hmm. open_deleted_file() will still need to get a directory... so it >> >>> will still need a path. Perhaps open("/foo/bar/mnt", O_DELETED) would >> >>> be acceptable interface? >> >>> Pavel >> >> ...and what's the big plan to make this work on anything other than ext4 and btrfs? >> >> >> >> Cheers, >> >> Trond >> > >> > I know that change can be a good thing, but are we really solving a pressing problem given that application developers have dealt with open/rename as the way to get "atomic" file creation for several decades now ? >> >> Using open()+rename() has side effects: >> - changes ctime/mtime on parent directory >> - leaves temporary file in path during creation >> - leaves temporary file in namespace during operations, and after crash > > So what is the actual problem that is being solved? Yes, the above may > be disadvantages, but none of them have proven to be show-stoppers so > far. > > So far, I've seen no justification for Andy's atomicity requirement > other than "it would be nice if...". That's not enough IMO... ISTM vpsendfile (or whatever it's called) plus a way to create deleted files plus a way to relink deleted files gives atomic copies. Perhaps this is less efficient than would be ideal for OCFS2, though. --Andy -- 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