NAS-115465 / 22.12 / expose ZFS_ACL_TRIVIAL to users (openzfs#52)

Add ACL_IS_TRIVIAL and ACL_IS_DIR flags as ACL-wide flags
in the system.nfs4_acl_xdr generated on getxattr requests.

This are non-RFC flags that are useful for userspace applications
(especially the ACL_IS_TRIVIAL flag as it can be used to avoid
relatively expensive ACL-related operations).

Also add system.nfs4_acl_xdr to xattr results if ACL is not trivial.
This duplicates POSIX ACL behavior where whether an ACL is
set on a path can be determined via listxattr(). Since the ACL
is not actually removed, we check whether the ZFS_ACL_TRIVIAL
is set. If the flag is not set, then we omit the xattr name from
the list. This allows users to determine whether ACL is trivial from
listxattr().

Signed-off-by: Andrew Walker <awalker@ixsystems.com>

include/os/linux/spl/sys/acl.h

@@ -83,6 +83,8 @@ typedef struct ace_object {
 #define	ACL_PROTECTED					0x0002
 #define	ACL_DEFAULTED					0x0004
 #define	ACL_FLAGS_ALL	(ACL_AUTO_INHERIT|ACL_PROTECTED|ACL_DEFAULTED)
+#define	ACL_IS_TRIVIAL					0x10000
+#define	ACL_IS_DIR					0x20000
 
 #define	ACE_ACCESS_ALLOWED_COMPOUND_ACE_TYPE		0x04
 #define	ACE_ACCESS_ALLOWED_OBJECT_ACE_TYPE		0x05

module/os/linux/zfs/zfs_acl.c

@@ -2032,6 +2032,10 @@ zfs_getacl(znode_t *zp, vsecattr_t *vsecp, boolean_t skipaclchk, cred_t *cr)
 			vsecp->vsa_aclflags |= ACL_PROTECTED;
 		if (zp->z_pflags & ZFS_ACL_AUTO_INHERIT)
 			vsecp->vsa_aclflags |= ACL_AUTO_INHERIT;
+		if (zp->z_pflags & ZFS_ACL_TRIVIAL)
+			vsecp->vsa_aclflags |= ACL_IS_TRIVIAL;
+		if (S_ISDIR(ZTOI(zp)->i_mode))
+			vsecp->vsa_aclflags |= ACL_IS_DIR;
 	}
 
 	mutex_exit(&zp->z_acl_lock);

module/os/linux/zfs/zpl_xattr.c

@@ -274,6 +274,14 @@ zpl_xattr_list(struct dentry *dentry, char *buffer, size_t buffer_size)
 	ZPL_VERIFY_ZP(zp);
 	rw_enter(&zp->z_xattr_lock, RW_READER);
 
+	if ((zfsvfs->z_acl_type == ZFS_ACLTYPE_NFSV4) &&
+	    ((zp->z_pflags & ZFS_ACL_TRIVIAL) == 0)) {
+		error = zpl_xattr_filldir(&xf, NFS41ACL_XATTR,
+		    sizeof (NFS41ACL_XATTR) - 1);
+		if (error)
+			goto out;
+	}
+
 	if (zfsvfs->z_use_sa && zp->z_is_sa) {
 		error = zpl_xattr_list_sa(&xf);
 		if (error)
@@ -1705,7 +1713,7 @@ nfsacl41i_to_zfsacl(const nfsacl41i *nacl, vsecattr_t *_vsecp)
 	vsecattr_t vsecp;
 
 	vsecp.vsa_aclcnt = nacl->na41_aces.na41_aces_len;
-	vsecp.vsa_aclflags = nacl->na41_flag;
+	vsecp.vsa_aclflags = nacl->na41_flag & ACL_FLAGS_ALL;
 	vsecp.vsa_aclentsz = vsecp.vsa_aclcnt * sizeof (ace_t);
 	vsecp.vsa_mask = (VSA_ACE | VSA_ACE_ACLFLAGS);
 	vsecp.vsa_aclentp = kmem_alloc(vsecp.vsa_aclentsz, KM_SLEEP);