Re: [PATCH v1 0/3] Allow knfsd to use atomic_open()

[Benjamin Coddington]

On 26 Nov 2025, at 19:36, NeilBrown wrote:
> It isn't so much that the change is incomplete.  Rather, the change
> introduces a regression.
>
> The old code was
>
> -	error = vfs_create(mnt_idmap(path->mnt),
> -			   d_inode(path->dentry->d_parent),
> -			   path->dentry, mode, true);
>
>
> Note the "true" at the end.  This instructs nfs_create() to pass O_EXCL
> to nfs_do_create() so an over-the-wire exclusive create is performed.
>
> The new code is
>
> +		dentry = atomic_open(path, dentry, file, flags, mode);
>
> Where "flags" is oflags from nfsd4_vfs_create() which is
>    O_CREAT| O_LARGEFILE | O_(read/write/rdwr)
> and no O_EXCL.
> (When atomic_open is called by lookup_open, "open_flag" is passed which
> might contain O_EXCL).

Of course, you're quite right, I should put more effort into trying to
understand your very first reply.

Fixing this up seems simple enough, I think we just need to do this on top
of what's here:

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 7e39234e0649..6990ba92bca1 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -202,6 +202,9 @@ nfsd4_vfs_create(struct svc_fh *fhp, struct dentry **child,
        int oflags;

        oflags = O_CREAT | O_LARGEFILE;
+       if (nfsd4_create_is_exclusive(open->op_createmode))
+               oflags |= O_EXCL;
+
        switch (open->op_share_access & NFS4_SHARE_ACCESS_BOTH) {
        case NFS4_SHARE_ACCESS_WRITE:
                oflags |= O_WRONLY;

I will send this through my re-export testing, but I don't think that its
going to produce different results because we lack a multi-client test to
detect cases for O_EXCL.

Ben