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From:   Ondrej Valousek <ondrej.valousek.xm@renesas.com>
To:     "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Subject: Patch nfs4 server to advertise usage of v4 ACLs
Thread-Topic: Patch nfs4 server to advertise usage of v4 ACLs
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Date:   Wed, 19 Oct 2022 12:46:39 +0000
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Hi list,
I was trying to address an issue described in
https://bugzilla.redhat.com/show_bug.cgi?id=3D767584
basically AFAIK RFC7530 instructs v4 NFS server to send a fake ACLs even wh=
en the there is actually no ACLs (aside of standard Unix attrs) defined.
This means the v4 client has no easy way to figure out if there are ACLs on=
 the file/directory or not, hence tools like 'ls -l' can't display the '+' =
character in front of file/directory much like on FS mounted with NFSv3.

I was trying this address this issue with this (sort of naive) patch:

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 1da721515b61..ad9324b25b7e 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -3182,7 +3182,7 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc=
_fh *fhp,
                p =3D xdr_reserve_space(xdr, 4);
                if (!p)
                        goto out_resource;
-               *p++ =3D cpu_to_be32(stat.mode & S_IALLUGO);
+               *p++ =3D cpu_to_be32((stat.mode & (S_IALLUGO | S_IFACL)));
        }
        if (bmval1 & FATTR4_WORD1_NO_TRUNC) {
                p =3D xdr_reserve_space(xdr, 4);
diff --git a/fs/stat.c b/fs/stat.c
index 28d2020ba1f4..da5b8bfbcd0f 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -20,6 +20,7 @@
=20
 #include <linux/uaccess.h>
 #include <asm/unistd.h>
+#include <linux/posix_acl.h>
=20
 #include "internal.h"
 #include "mount.h"
@@ -43,9 +44,15 @@
 void generic_fillattr(struct user_namespace *mnt_userns, struct inode *ino=
de,
                      struct kstat *stat)
 {
+       struct posix_acl *pacl =3D get_acl(inode, ACL_TYPE_ACCESS);
+
        stat->dev =3D inode->i_sb->s_dev;
        stat->ino =3D inode->i_ino;
        stat->mode =3D inode->i_mode;
+       if(pacl){       /* ACL of some kind is present */
+               stat->mode |=3D S_IFACL;
+               posix_acl_release(pacl);
+       }
        stat->nlink =3D inode->i_nlink;
        stat->uid =3D i_uid_into_mnt(mnt_userns, inode);
        stat->gid =3D i_gid_into_mnt(mnt_userns, inode);
diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
index 1500a0f58041..2ab453ed8bfb 100644
--- a/include/uapi/linux/stat.h
+++ b/include/uapi/linux/stat.h
@@ -6,6 +6,7 @@
=20
 #if defined(__KERNEL__) || !defined(__GLIBC__) || (__GLIBC__ < 2)
=20
+#define S_IFACL 00200000       /* ACL of some kind is present */
 #define S_IFMT  00170000
 #define S_IFSOCK 0140000
 #define S_IFLNK         0120000

... which aims to inform the remote nfs client about that no real ACLs are =
present.
Question - is something similar possible or doable?

Many thanks.