Hello Pip, Pip Cet: > I've had a look at the relevant code in fs/namei.c, and it appears to me > the problem is that lookup_open(), in the absence of an ->atomic_open > method, falls back to creating a file with vfs_create, then opening it with > vfs_open, which fails in this case. It's not clear to me what a good fix > would be, though implementing ->atomic_open should work.
You analized very well. I've tried implementing aufs atomic_open several years before, but it was complicated and I decided that aufs doesn't support atomic_open. It was not a big issue until now and I have not received such mail. Something might changed recently? - nfs4 becomes popular - vfs or nfs4 internal implementation changed No, the changes in outer world should not be related to this problem. You reported other versions of aufs failed similarly. And I guess aufs have never succeeded open(O_WRONLY|O_CREAT, 0400) on nfs4 branch. Probably it is just a matter of fact that who report first. > As an experiment, I've disabled nfs4's ->atomic_open method, and the result > was that with the modified kernel, my test program fails even directly on > the nfs file system. It still succeeds both directly on a ramfs and on an > aufs using said ramfs, but that appears to be because ramfs has no ->open > at all Right. I've confirmed nfs fh_verify() rejects open(O_WRONLY) for the already created readonly file. I think aufs should try supporting atomic_open (while it is complicated) now. As a first step, would you try this patch? It is just to confirm the scenario and prints a kern.info log where aufs should call ->atomic_open(). I'd ask you to try verious patterns. By this patch aufs will prints a msg. In other words, when you see an error without the aufs log msg, it means this first step is not good. Thanx for good analysis and report J. R. Okajima
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