On Mon, Dec 05, 2016 at 10:28:18AM +0100, Miklos Szeredi wrote: > [Added a few more CCs] > > On Mon, Dec 5, 2016 at 1:51 AM, Patrick Plagwitz > <Patrick_Plagwitz@xxxxxx> wrote: > > Mounting an overlayfs with an NFSv4 lowerdir and an ext4 upperdir causes copy_up operations, specifically the function copy_up.c:ovl_copy_xattr, to fail with EOPNOTSUPP. > > For example, having the following folders: > > > > |- nfs <- NFSv4 is mounted here > > |--|- folder > > |- root <- ext4 is mounted here > > |- work <- also ext4 > > |- merged <- overlay is mounted here with > > lowerdir=nfs,upperdir=root,workdir=work > > > > And calling > > # touch merged/folder/file > > will print > > touch: cannot touch 'merged/folder/file': Operation not supported > > > > This is because NFS returns the xattr system.nfs4_acl with an empty value even if no NFS ACLs are in use in the lower filesystem. Trying to set this xattr in the upperdir > > fails because ext4 does not support it. > > > > Fix this by explicitly checking for the name of the xattr and an empty value and ignoring EOPNOTSUPP if both things match. > > > > Signed-off-by: Patrick Plagwitz <patrick_plagwitz@xxxxxx> > > --- > > Maybe NFS could be changed to not return empty system.nfs4_acl values, I don't know. In any case, to support upperdir ext4 + lowerdir NFSv4, returning the error code from > > vfs_setxattr with this xattr name must be avoided as long as the value is empty. > > > > diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c > > index 36795ee..505b86e 100644 > > --- a/fs/overlayfs/copy_up.c > > +++ b/fs/overlayfs/copy_up.c > > @@ -123,6 +123,9 @@ int ovl_copy_xattr(struct dentry *old, struct dentry *new) > > continue; /* Discard */ > > } > > error = vfs_setxattr(new, name, value, size, 0); > > + if (error == -EOPNOTSUPP && *value == '\0' && > > + strcmp(name, "system.nfs4_acl") == 0) > > + error = 0; > > if (error) > > break; > > } > > I agree that this should be fixed, but adding such exceptions for > certain filesystems or xattrs is not the proper way, IMO. > > Can NFS people comment on this? Where does the nfs4_acl come from? This is the interface the NFS client provides for applications to modify NFSv4 ACLs on servers that support them. > What can overlayfs do if it's a non-empty ACL? As little as possible. You can't copy it up, can you? So any attempt to support it is going to be incomplete. > Does knfsd translate posix ACL into NFS acl? If so, we can translate > back. Should we do a generic POSIX<->NFS acl translator? knsd does translate between POSIX and NFSv4 ACLs. It's a complicated algorithm, and lossy (in the NFSv4->POSIX direction). The client developers have been understandably reluctant to have anything to do with it. So, I think listxattr should omit system.nfs4_acl, and attempts to set/get the attribute should error out. The same should apply to any "system." attribute not supported by both filesystems, I think? I don't understand overlayfs very well, though. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
