diff --git a/include/sys/fs/zfs.h b/include/sys/fs/zfs.h
index e7fc2f459..6c0463e13 100644
--- a/include/sys/fs/zfs.h
+++ b/include/sys/fs/zfs.h
@@ -1709,7 +1709,6 @@ typedef enum {
 #define	ZFS_EV_HIST_DSID	"history_dsid"
 #define	ZFS_EV_RESILVER_TYPE	"resilver_type"
 
-
 /*
  * We currently support block sizes from 512 bytes to 16MB.
  * The benefits of larger blocks, and thus larger IO, need to be weighed
@@ -1731,7 +1730,6 @@ typedef enum {
 #define	SPA_OLD_MAXBLOCKSIZE	(1ULL << SPA_OLD_MAXBLOCKSHIFT)
 #define	SPA_MAXBLOCKSIZE	(1ULL << SPA_MAXBLOCKSHIFT)
 
-
 /* supported encryption algorithms */
 enum zio_encrypt {
 	ZIO_CRYPT_INHERIT = 0,
@@ -1749,6 +1747,34 @@ enum zio_encrypt {
 #define	ZIO_CRYPT_ON_VALUE	ZIO_CRYPT_AES_256_GCM
 #define	ZIO_CRYPT_DEFAULT	ZIO_CRYPT_OFF
 
+/*
+ * xattr namespace prefixes.  These are forbidden in xattr names.
+ *
+ * For cross-platform compatibility, xattrs in the user namespace should not be
+ * prefixed with the namespace name, but for backwards compatibility with older
+ * ZFS on Linux versions we do prefix the namespace.
+ */
+#define	ZFS_XA_NS_FREEBSD_PREFIX		"freebsd:"
+#define	ZFS_XA_NS_FREEBSD_PREFIX_LEN		strlen("freebsd:")
+#define	ZFS_XA_NS_LINUX_SECURITY_PREFIX		"security."
+#define	ZFS_XA_NS_LINUX_SECURITY_PREFIX_LEN	strlen("security.")
+#define	ZFS_XA_NS_LINUX_SYSTEM_PREFIX		"system."
+#define	ZFS_XA_NS_LINUX_SYSTEM_PREFIX_LEN	strlen("system.")
+#define	ZFS_XA_NS_LINUX_TRUSTED_PREFIX		"trusted."
+#define	ZFS_XA_NS_LINUX_TRUSTED_PREFIX_LEN	strlen("trusted.")
+#define	ZFS_XA_NS_LINUX_USER_PREFIX		"user."
+#define	ZFS_XA_NS_LINUX_USER_PREFIX_LEN		strlen("user.")
+
+#define	ZFS_XA_NS_PREFIX_MATCH(ns, name) \
+	(strncmp(name, ZFS_XA_NS_##ns##_PREFIX, \
+	ZFS_XA_NS_##ns##_PREFIX_LEN) == 0)
+
+#define	ZFS_XA_NS_PREFIX_FORBIDDEN(name) \
+	(ZFS_XA_NS_PREFIX_MATCH(FREEBSD, name) || \
+	    ZFS_XA_NS_PREFIX_MATCH(LINUX_SECURITY, name) || \
+	    ZFS_XA_NS_PREFIX_MATCH(LINUX_SYSTEM, name) || \
+	    ZFS_XA_NS_PREFIX_MATCH(LINUX_TRUSTED, name) || \
+	    ZFS_XA_NS_PREFIX_MATCH(LINUX_USER, name))
 
 #ifdef	__cplusplus
 }
diff --git a/man/man4/zfs.4 b/man/man4/zfs.4
index b2e850f84..bb3cd2243 100644
--- a/man/man4/zfs.4
+++ b/man/man4/zfs.4
@@ -2129,6 +2129,30 @@ When enabled, the maximum number of pending allocations per top-level vdev
 is limited by
 .Sy zfs_vdev_queue_depth_pct .
 .
+.It Sy zfs_xattr_compat Ns = Ns 0 Ns | Ns 1 Pq int
+Control the naming scheme used when setting new xattrs in the user namespace.
+If
+.Sy 0
+.Pq the default on Linux ,
+user namespace xattr names are prefixed with the namespace, to be backwards
+compatible with previous versions of ZFS on Linux.
+If
+.Sy 1
+.Pq the default on Fx ,
+user namespace xattr names are not prefixed, to be backwards compatible with
+previous versions of ZFS on illumos and
+.Fx .
+.Pp
+Either naming scheme can be read on this and future versions of ZFS, regardless
+of this tunable, but legacy ZFS on illumos or
+.Fx
+are unable to read user namespace xattrs written in the Linux format, and
+legacy versions of ZFS on Linux are unable to read user namespace xattrs written
+in the legacy ZFS format.
+.Pp
+An existing xattr with the alternate naming scheme is removed when overwriting
+the xattr so as to not accumulate duplicates.
+.
 .It Sy zio_requeue_io_start_cut_in_line Ns = Ns Sy 0 Ns | Ns 1 Pq int
 Prioritize requeued I/O.
 .
diff --git a/module/os/freebsd/zfs/zfs_vnops_os.c b/module/os/freebsd/zfs/zfs_vnops_os.c
index 55e22cb91..b36862bba 100644
--- a/module/os/freebsd/zfs/zfs_vnops_os.c
+++ b/module/os/freebsd/zfs/zfs_vnops_os.c
@@ -5253,43 +5253,56 @@ zfs_freebsd_pathconf(struct vop_pathconf_args *ap)
 	}
 }
 
+static int zfs_xattr_compat = 1;
+
+static int
+zfs_check_attrname(const char *name)
+{
+	/* We don't allow '/' character in attribute name. */
+	if (strchr(name, '/') != NULL)
+		return (SET_ERROR(EINVAL));
+	/* We don't allow attribute names that start with a namespace prefix. */
+	if (ZFS_XA_NS_PREFIX_FORBIDDEN(name))
+		return (SET_ERROR(EINVAL));
+	return (0);
+}
+
 /*
  * FreeBSD's extended attributes namespace defines file name prefix for ZFS'
  * extended attribute name:
  *
- *	NAMESPACE	PREFIX
- *	system		freebsd:system:
- *	user		(none, can be used to access ZFS fsattr(5) attributes
- *			created on Solaris)
+ *	NAMESPACE	XATTR_COMPAT	PREFIX
+ *	system		*		freebsd:system:
+ *	user		1		(none, can be used to access ZFS
+ *					fsattr(5) attributes created on Solaris)
+ *	user		0		user.
  */
 static int
 zfs_create_attrname(int attrnamespace, const char *name, char *attrname,
-    size_t size)
+    size_t size, boolean_t compat)
 {
 	const char *namespace, *prefix, *suffix;
 
-	/* We don't allow '/' character in attribute name. */
-	if (strchr(name, '/') != NULL)
-		return (SET_ERROR(EINVAL));
-	/* We don't allow attribute names that start with "freebsd:" string. */
-	if (strncmp(name, "freebsd:", 8) == 0)
-		return (SET_ERROR(EINVAL));
-
 	bzero(attrname, size);
 
 	switch (attrnamespace) {
 	case EXTATTR_NAMESPACE_USER:
-#if 0
-		prefix = "freebsd:";
-		namespace = EXTATTR_NAMESPACE_USER_STRING;
-		suffix = ":";
-#else
-		/*
-		 * This is the default namespace by which we can access all
-		 * attributes created on Solaris.
-		 */
-		prefix = namespace = suffix = "";
-#endif
+		if (compat) {
+			/*
+			 * This is the default namespace by which we can access
+			 * all attributes created on Solaris.
+			 */
+			prefix = namespace = suffix = "";
+		} else {
+			/*
+			 * This is compatible with the user namespace encoding
+			 * on Linux prior to xattr_compat, but nothing
+			 * else.
+			 */
+			prefix = "";
+			namespace = "user";
+			suffix = ".";
+		}
 		break;
 	case EXTATTR_NAMESPACE_SYSTEM:
 		prefix = "freebsd:";
@@ -5411,6 +5424,27 @@ zfs_getextattr_sa(struct vop_getextattr_args *ap, const char *attrname)
 	return (0);
 }
 
+static int
+zfs_getextattr_impl(struct vop_getextattr_args *ap, boolean_t compat)
+{
+	znode_t *zp = VTOZ(ap->a_vp);
+	zfsvfs_t *zfsvfs = ZTOZSB(zp);
+	char attrname[EXTATTR_MAXNAMELEN+1];
+	int error;
+
+	error = zfs_create_attrname(ap->a_attrnamespace, ap->a_name, attrname,
+	    sizeof (attrname), compat);
+	if (error != 0)
+		return (error);
+
+	error = ENOENT;
+	if (zfsvfs->z_use_sa && zp->z_is_sa)
+		error = zfs_getextattr_sa(ap, attrname);
+	if (error == ENOENT)
+		error = zfs_getextattr_dir(ap, attrname);
+	return (error);
+}
+
 /*
  * Vnode operation to retrieve a named extended attribute.
  */
@@ -5419,7 +5453,6 @@ zfs_getextattr(struct vop_getextattr_args *ap)
 {
 	znode_t *zp = VTOZ(ap->a_vp);
 	zfsvfs_t *zfsvfs = ZTOZSB(zp);
-	char attrname[EXTATTR_MAXNAMELEN+1];
 	int error;
 
 	/*
@@ -5433,8 +5466,7 @@ zfs_getextattr(struct vop_getextattr_args *ap)
 	if (error != 0)
 		return (SET_ERROR(error));
 
-	error = zfs_create_attrname(ap->a_attrnamespace, ap->a_name, attrname,
-	    sizeof (attrname));
+	error = zfs_check_attrname(ap->a_name);
 	if (error != 0)
 		return (error);
 
@@ -5442,10 +5474,17 @@ zfs_getextattr(struct vop_getextattr_args *ap)
 	ZFS_ENTER(zfsvfs);
 	ZFS_VERIFY_ZP(zp)
 	rw_enter(&zp->z_xattr_lock, RW_READER);
-	if (zfsvfs->z_use_sa && zp->z_is_sa)
-		error = zfs_getextattr_sa(ap, attrname);
-	if (error == ENOENT)
-		error = zfs_getextattr_dir(ap, attrname);
+
+	error = zfs_getextattr_impl(ap, zfs_xattr_compat);
+	if ((error == ENOENT || error == ENOATTR) &&
+	    ap->a_attrnamespace == EXTATTR_NAMESPACE_USER) {
+		/*
+		 * Fall back to the alternate namespace format if we failed to
+		 * find a user xattr.
+		 */
+		error = zfs_getextattr_impl(ap, !zfs_xattr_compat);
+	}
+
 	rw_exit(&zp->z_xattr_lock);
 	ZFS_EXIT(zfsvfs);
 	if (error == ENOENT)
@@ -5528,6 +5567,27 @@ zfs_deleteextattr_sa(struct vop_deleteextattr_args *ap, const char *attrname)
 	return (error);
 }
 
+static int
+zfs_deleteextattr_impl(struct vop_deleteextattr_args *ap, boolean_t compat)
+{
+	znode_t *zp = VTOZ(ap->a_vp);
+	zfsvfs_t *zfsvfs = ZTOZSB(zp);
+	char attrname[EXTATTR_MAXNAMELEN+1];
+	int error;
+
+	error = zfs_create_attrname(ap->a_attrnamespace, ap->a_name, attrname,
+	    sizeof (attrname), compat);
+	if (error != 0)
+		return (error);
+
+	error = ENOENT;
+	if (zfsvfs->z_use_sa && zp->z_is_sa)
+		error = zfs_deleteextattr_sa(ap, attrname);
+	if (error == ENOENT)
+		error = zfs_deleteextattr_dir(ap, attrname);
+	return (error);
+}
+
 /*
  * Vnode operation to remove a named attribute.
  */
@@ -5536,7 +5596,6 @@ zfs_deleteextattr(struct vop_deleteextattr_args *ap)
 {
 	znode_t *zp = VTOZ(ap->a_vp);
 	zfsvfs_t *zfsvfs = ZTOZSB(zp);
-	char attrname[EXTATTR_MAXNAMELEN+1];
 	int error;
 
 	/*
@@ -5550,32 +5609,24 @@ zfs_deleteextattr(struct vop_deleteextattr_args *ap)
 	if (error != 0)
 		return (SET_ERROR(error));
 
-	error = zfs_create_attrname(ap->a_attrnamespace, ap->a_name, attrname,
-	    sizeof (attrname));
+	error = zfs_check_attrname(ap->a_name);
 	if (error != 0)
 		return (error);
 
-	size_t size = 0;
-	struct vop_getextattr_args vga = {
-		.a_vp = ap->a_vp,
-		.a_size = &size,
-		.a_cred = ap->a_cred,
-		.a_td = ap->a_td,
-	};
-	error = ENOENT;
 	ZFS_ENTER(zfsvfs);
 	ZFS_VERIFY_ZP(zp);
 	rw_enter(&zp->z_xattr_lock, RW_WRITER);
-	if (zfsvfs->z_use_sa && zp->z_is_sa) {
-		error = zfs_getextattr_sa(&vga, attrname);
-		if (error == 0)
-			error = zfs_deleteextattr_sa(ap, attrname);
-	}
-	if (error == ENOENT) {
-		error = zfs_getextattr_dir(&vga, attrname);
-		if (error == 0)
-			error = zfs_deleteextattr_dir(ap, attrname);
+
+	error = zfs_deleteextattr_impl(ap, zfs_xattr_compat);
+	if ((error == ENOENT || error == ENOATTR) &&
+	    ap->a_attrnamespace == EXTATTR_NAMESPACE_USER) {
+		/*
+		 * Fall back to the alternate namespace format if we failed to
+		 * find a user xattr.
+		 */
+		error = zfs_deleteextattr_impl(ap, !zfs_xattr_compat);
 	}
+
 	rw_exit(&zp->z_xattr_lock);
 	ZFS_EXIT(zfsvfs);
 	if (error == ENOENT)
@@ -5675,6 +5726,56 @@ zfs_setextattr_sa(struct vop_setextattr_args *ap, const char *attrname)
 	return (error);
 }
 
+static int
+zfs_setextattr_impl(struct vop_setextattr_args *ap, boolean_t compat)
+{
+	znode_t *zp = VTOZ(ap->a_vp);
+	zfsvfs_t *zfsvfs = ZTOZSB(zp);
+	char attrname[EXTATTR_MAXNAMELEN+1];
+	int error;
+
+	error = zfs_create_attrname(ap->a_attrnamespace, ap->a_name, attrname,
+	    sizeof (attrname), compat);
+	if (error != 0)
+		return (error);
+
+	struct vop_deleteextattr_args vda = {
+		.a_vp = ap->a_vp,
+		.a_attrnamespace = ap->a_attrnamespace,
+		.a_name = ap->a_name,
+		.a_cred = ap->a_cred,
+		.a_td = ap->a_td,
+	};
+	error = ENOENT;
+	if (zfsvfs->z_use_sa && zp->z_is_sa && zfsvfs->z_xattr_sa) {
+		error = zfs_setextattr_sa(ap, attrname);
+		if (error == 0) {
+			/*
+			 * Successfully put into SA, we need to clear the one
+			 * in dir if present.
+			 */
+			zfs_deleteextattr_dir(&vda, attrname);
+		}
+	}
+	if (error != 0) {
+		error = zfs_setextattr_dir(ap, attrname);
+		if (error == 0 && zp->z_is_sa) {
+			/*
+			 * Successfully put into dir, we need to clear the one
+			 * in SA if present.
+			 */
+			zfs_deleteextattr_sa(&vda, attrname);
+		}
+	}
+	if (error == 0 && ap->a_attrnamespace == EXTATTR_NAMESPACE_USER) {
+		/*
+		 * Also clear all versions of the alternate compat name.
+		 */
+		zfs_deleteextattr_impl(&vda, !compat);
+	}
+	return (error);
+}
+
 /*
  * Vnode operation to set a named attribute.
  */
@@ -5683,7 +5784,6 @@ zfs_setextattr(struct vop_setextattr_args *ap)
 {
 	znode_t *zp = VTOZ(ap->a_vp);
 	zfsvfs_t *zfsvfs = ZTOZSB(zp);
-	char attrname[EXTATTR_MAXNAMELEN+1];
 	int error;
 
 	/*
@@ -5697,38 +5797,16 @@ zfs_setextattr(struct vop_setextattr_args *ap)
 	if (error != 0)
 		return (SET_ERROR(error));
 
-	error = zfs_create_attrname(ap->a_attrnamespace, ap->a_name, attrname,
-	    sizeof (attrname));
+	error = zfs_check_attrname(ap->a_name);
 	if (error != 0)
 		return (error);
 
-	struct vop_deleteextattr_args vda = {
-		.a_vp = ap->a_vp,
-		.a_cred = ap->a_cred,
-		.a_td = ap->a_td,
-	};
-	error = ENOENT;
 	ZFS_ENTER(zfsvfs);
 	ZFS_VERIFY_ZP(zp);
 	rw_enter(&zp->z_xattr_lock, RW_WRITER);
-	if (zfsvfs->z_use_sa && zp->z_is_sa && zfsvfs->z_xattr_sa) {
-		error = zfs_setextattr_sa(ap, attrname);
-		if (error == 0)
-			/*
-			 * Successfully put into SA, we need to clear the one
-			 * in dir if present.
-			 */
-			zfs_deleteextattr_dir(&vda, attrname);
-	}
-	if (error) {
-		error = zfs_setextattr_dir(ap, attrname);
-		if (error == 0 && zp->z_is_sa)
-			/*
-			 * Successfully put into dir, we need to clear the one
-			 * in SA if present.
-			 */
-			zfs_deleteextattr_sa(&vda, attrname);
-	}
+
+	error = zfs_setextattr_impl(ap, zfs_xattr_compat);
+
 	rw_exit(&zp->z_xattr_lock);
 	ZFS_EXIT(zfsvfs);
 	return (error);
@@ -5808,7 +5886,7 @@ zfs_listextattr_dir(struct vop_listextattr_args *ap, const char *attrprefix)
 			if (dp->d_type != DT_REG && dp->d_type != DT_UNKNOWN)
 				continue;
 			else if (plen == 0 &&
-			    strncmp(dp->d_name, "freebsd:", 8) == 0)
+			    ZFS_XA_NS_PREFIX_FORBIDDEN(dp->d_name))
 				continue;
 			else if (strncmp(dp->d_name, attrprefix, plen) != 0)
 				continue;
@@ -5856,7 +5934,7 @@ zfs_listextattr_sa(struct vop_listextattr_args *ap, const char *attrprefix)
 		ASSERT3U(nvpair_type(nvp), ==, DATA_TYPE_BYTE_ARRAY);
 
 		const char *name = nvpair_name(nvp);
-		if (plen == 0 && strncmp(name, "freebsd:", 8) == 0)
+		if (plen == 0 && ZFS_XA_NS_PREFIX_FORBIDDEN(name))
 			continue;
 		else if (strncmp(name, attrprefix, plen) != 0)
 			continue;
@@ -5883,6 +5961,26 @@ zfs_listextattr_sa(struct vop_listextattr_args *ap, const char *attrprefix)
 	return (error);
 }
 
+static int
+zfs_listextattr_impl(struct vop_listextattr_args *ap, boolean_t compat)
+{
+	znode_t *zp = VTOZ(ap->a_vp);
+	zfsvfs_t *zfsvfs = ZTOZSB(zp);
+	char attrprefix[16];
+	int error;
+
+	error = zfs_create_attrname(ap->a_attrnamespace, "", attrprefix,
+	    sizeof (attrprefix), compat);
+	if (error != 0)
+		return (error);
+
+	if (zfsvfs->z_use_sa && zp->z_is_sa)
+		error = zfs_listextattr_sa(ap, attrprefix);
+	if (error == 0)
+		error = zfs_listextattr_dir(ap, attrprefix);
+	return (error);
+}
+
 /*
  * Vnode operation to retrieve extended attributes on a vnode.
  */
@@ -5891,7 +5989,6 @@ zfs_listextattr(struct vop_listextattr_args *ap)
 {
 	znode_t *zp = VTOZ(ap->a_vp);
 	zfsvfs_t *zfsvfs = ZTOZSB(zp);
-	char attrprefix[16];
 	int error;
 
 	if (ap->a_size != NULL)
@@ -5908,18 +6005,16 @@ zfs_listextattr(struct vop_listextattr_args *ap)
 	if (error != 0)
 		return (SET_ERROR(error));
 
-	error = zfs_create_attrname(ap->a_attrnamespace, "", attrprefix,
-	    sizeof (attrprefix));
-	if (error != 0)
-		return (error);
-
 	ZFS_ENTER(zfsvfs);
 	ZFS_VERIFY_ZP(zp);
 	rw_enter(&zp->z_xattr_lock, RW_READER);
-	if (zfsvfs->z_use_sa && zp->z_is_sa)
-		error = zfs_listextattr_sa(ap, attrprefix);
-	if (error == 0)
-		error = zfs_listextattr_dir(ap, attrprefix);
+
+	error = zfs_listextattr_impl(ap, zfs_xattr_compat);
+	if (error == 0 && ap->a_attrnamespace == EXTATTR_NAMESPACE_USER) {
+		/* Also list user xattrs with the alternate format. */
+		error = zfs_listextattr_impl(ap, !zfs_xattr_compat);
+	}
+
 	rw_exit(&zp->z_xattr_lock);
 	ZFS_EXIT(zfsvfs);
 	return (error);
@@ -6257,3 +6352,6 @@ struct vop_vector zfs_shareops = {
 #endif
 };
 VFS_VOP_VECTOR_REGISTER(zfs_shareops);
+
+ZFS_MODULE_PARAM(zfs, zfs_, xattr_compat, INT, ZMOD_RW,
+	"Use legacy ZFS xattr naming for writing new user namespace xattrs");
diff --git a/module/os/linux/zfs/zpl_xattr.c b/module/os/linux/zfs/zpl_xattr.c
index a1921ed08..ce1815771 100644
--- a/module/os/linux/zfs/zpl_xattr.c
+++ b/module/os/linux/zfs/zpl_xattr.c
@@ -84,6 +84,12 @@
 #include <sys/vfs.h>
 #include <sys/zpl.h>
 
+enum xattr_permission {
+	XAPERM_DENY,
+	XAPERM_ALLOW,
+	XAPERM_COMPAT,
+};
+
 typedef struct xattr_filldir {
 	size_t size;
 	size_t offset;
@@ -91,33 +97,10 @@ typedef struct xattr_filldir {
 	struct dentry *dentry;
 } xattr_filldir_t;
 
-static const struct xattr_handler *zpl_xattr_handler(const char *);
+static enum xattr_permission zpl_xattr_permission(xattr_filldir_t *,
+    const char *, int);
 
-static int
-zpl_xattr_permission(xattr_filldir_t *xf, const char *name, int name_len)
-{
-	static const struct xattr_handler *handler;
-	struct dentry *d = xf->dentry;
-
-	handler = zpl_xattr_handler(name);
-	if (!handler)
-		return (0);
-
-	if (handler->list) {
-#if defined(HAVE_XATTR_LIST_SIMPLE)
-		if (!handler->list(d))
-			return (0);
-#elif defined(HAVE_XATTR_LIST_DENTRY)
-		if (!handler->list(d, NULL, 0, name, name_len, 0))
-			return (0);
-#elif defined(HAVE_XATTR_LIST_HANDLER)
-		if (!handler->list(handler, d, NULL, 0, name, name_len))
-			return (0);
-#endif
-	}
-
-	return (1);
-}
+static int zfs_xattr_compat = 0;
 
 /*
  * Determine is a given xattr name should be visible and if so copy it
@@ -126,10 +109,27 @@ zpl_xattr_permission(xattr_filldir_t *xf, const char *name, int name_len)
 static int
 zpl_xattr_filldir(xattr_filldir_t *xf, const char *name, int name_len)
 {
+	enum xattr_permission perm;
+
 	/* Check permissions using the per-namespace list xattr handler. */
-	if (!zpl_xattr_permission(xf, name, name_len))
+	perm = zpl_xattr_permission(xf, name, name_len);
+	if (perm == XAPERM_DENY)
 		return (0);
 
+	/* Prefix the name with "user." if it does not have a namespace. */
+	if (perm == XAPERM_COMPAT) {
+		if (xf->buf) {
+			if (xf->offset + XATTR_USER_PREFIX_LEN + 1 > xf->size)
+				return (-ERANGE);
+
+			memcpy(xf->buf + xf->offset, XATTR_USER_PREFIX,
+			    XATTR_USER_PREFIX_LEN);
+			xf->buf[xf->offset + XATTR_USER_PREFIX_LEN] = '\0';
+		}
+
+		xf->offset += XATTR_USER_PREFIX_LEN;
+	}
+
 	/* When xf->buf is NULL only calculate the required size. */
 	if (xf->buf) {
 		if (xf->offset + name_len + 1 > xf->size)
@@ -706,19 +706,28 @@ static int
 __zpl_xattr_user_get(struct inode *ip, const char *name,
     void *value, size_t size)
 {
-	char *xattr_name;
 	int error;
 	/* xattr_resolve_name will do this for us if this is defined */
 #ifndef HAVE_XATTR_HANDLER_NAME
 	if (strcmp(name, "") == 0)
 		return (-EINVAL);
 #endif
+	if (ZFS_XA_NS_PREFIX_FORBIDDEN(name))
+		return (-EINVAL);
 	if (!(ITOZSB(ip)->z_flags & ZSB_XATTR))
 		return (-EOPNOTSUPP);
 
-	xattr_name = kmem_asprintf("%s%s", XATTR_USER_PREFIX, name);
+	/*
+	 * Try to look up the name with the namespace prefix first for
+	 * compatibility with xattrs from this platform.  If that fails,
+	 * try again without the namespace prefix for compatibility with
+	 * other platforms.
+	 */
+	char *xattr_name = kmem_asprintf("%s%s", XATTR_USER_PREFIX, name);
 	error = zpl_xattr_get(ip, xattr_name, value, size);
 	kmem_strfree(xattr_name);
+	if (error == -ENODATA)
+		error = zpl_xattr_get(ip, name, value, size);
 
 	return (error);
 }
@@ -728,20 +737,59 @@ static int
 __zpl_xattr_user_set(struct inode *ip, const char *name,
     const void *value, size_t size, int flags)
 {
-	char *xattr_name;
-	int error;
+	int error = 0;
 	/* xattr_resolve_name will do this for us if this is defined */
 #ifndef HAVE_XATTR_HANDLER_NAME
 	if (strcmp(name, "") == 0)
 		return (-EINVAL);
 #endif
+	if (ZFS_XA_NS_PREFIX_FORBIDDEN(name))
+		return (-EINVAL);
 	if (!(ITOZSB(ip)->z_flags & ZSB_XATTR))
 		return (-EOPNOTSUPP);
 
-	xattr_name = kmem_asprintf("%s%s", XATTR_USER_PREFIX, name);
-	error = zpl_xattr_set(ip, xattr_name, value, size, flags);
-	kmem_strfree(xattr_name);
-
+	/*
+	 * Remove alternate compat version of the xattr so we only set the
+	 * version specified by the zfs_xattr_compat tunable.
+	 *
+	 * The following flags must be handled correctly:
+	 *
+	 *   XATTR_CREATE: fail if xattr already exists
+	 *   XATTR_REPLACE: fail if xattr does not exist
+	 */
+	char *prefixed_name = kmem_asprintf("%s%s", XATTR_USER_PREFIX, name);
+	const char *clear_name, *set_name;
+	if (zfs_xattr_compat) {
+		clear_name = prefixed_name;
+		set_name = name;
+	} else {
+		clear_name = name;
+		set_name = prefixed_name;
+	}
+	/*
+	 * Clear the old value with the alternative name format, if it exists.
+	 */
+	error = zpl_xattr_set(ip, clear_name, NULL, 0, flags);
+	/*
+	 * XATTR_CREATE was specified and we failed to clear the xattr
+	 * because it already exists.  Stop here.
+	 */
+	if (error == -EEXIST)
+		goto out;
+	/*
+	 * If XATTR_REPLACE was specified and we succeeded to clear
+	 * an xattr, we don't need to replace anything when setting
+	 * the new value.  If we failed with -ENODATA that's fine,
+	 * there was nothing to be cleared and we can ignore the error.
+	 */
+	if (error == 0)
+		flags &= ~XATTR_REPLACE;
+	/*
+	 * Set the new value with the configured name format.
+	 */
+	error = zpl_xattr_set(ip, set_name, value, size, flags);
+out:
+	kmem_strfree(prefixed_name);
 	return (error);
 }
 ZPL_XATTR_SET_WRAPPER(zpl_xattr_user_set);
@@ -1411,6 +1459,42 @@ zpl_xattr_handler(const char *name)
 	return (NULL);
 }
 
+static enum xattr_permission
+zpl_xattr_permission(xattr_filldir_t *xf, const char *name, int name_len)
+{
+	const struct xattr_handler *handler;
+	struct dentry *d __maybe_unused = xf->dentry;
+	enum xattr_permission perm = XAPERM_ALLOW;
+
+	handler = zpl_xattr_handler(name);
+	if (handler == NULL) {
+		/* Do not expose FreeBSD system namespace xattrs. */
+		if (ZFS_XA_NS_PREFIX_MATCH(FREEBSD, name))
+			return (XAPERM_DENY);
+		/*
+		 * Anything that doesn't match a known namespace gets put in the
+		 * user namespace for compatibility with other platforms.
+		 */
+		perm = XAPERM_COMPAT;
+		handler = &zpl_xattr_user_handler;
+	}
+
+	if (handler->list) {
+#if defined(HAVE_XATTR_LIST_SIMPLE)
+		if (!handler->list(d))
+			return (XAPERM_DENY);
+#elif defined(HAVE_XATTR_LIST_DENTRY)
+		if (!handler->list(d, NULL, 0, name, name_len, 0))
+			return (XAPERM_DENY);
+#elif defined(HAVE_XATTR_LIST_HANDLER)
+		if (!handler->list(handler, d, NULL, 0, name, name_len))
+			return (XAPERM_DENY);
+#endif
+	}
+
+	return (perm);
+}
+
 #if !defined(HAVE_POSIX_ACL_RELEASE) || defined(HAVE_POSIX_ACL_RELEASE_GPL_ONLY)
 struct acl_rel_struct {
 	struct acl_rel_struct *next;
@@ -1510,3 +1594,6 @@ zpl_posix_acl_release_impl(struct posix_acl *acl)
 		    NULL, TQ_SLEEP, ddi_get_lbolt() + ACL_REL_SCHED);
 }
 #endif
+
+ZFS_MODULE_PARAM(zfs, zfs_, xattr_compat, INT, ZMOD_RW,
+	"Use legacy ZFS xattr naming for writing new user namespace xattrs");
diff --git a/tests/runfiles/common.run b/tests/runfiles/common.run
index a7c34d0ea..0dfac459d 100644
--- a/tests/runfiles/common.run
+++ b/tests/runfiles/common.run
@@ -925,7 +925,7 @@ tags = ['functional', 'write_dirs']
 [tests/functional/xattr]
 tests = ['xattr_001_pos', 'xattr_002_neg', 'xattr_003_neg', 'xattr_004_pos',
     'xattr_005_pos', 'xattr_006_pos', 'xattr_007_neg',
-    'xattr_011_pos', 'xattr_012_pos', 'xattr_013_pos']
+    'xattr_011_pos', 'xattr_012_pos', 'xattr_013_pos', 'xattr_compat']
 tags = ['functional', 'xattr']
 
 [tests/functional/zvol/zvol_ENOSPC]
diff --git a/tests/runfiles/sanity.run b/tests/runfiles/sanity.run
index 8057d8148..383308bb5 100644
--- a/tests/runfiles/sanity.run
+++ b/tests/runfiles/sanity.run
@@ -602,7 +602,7 @@ tags = ['functional', 'vdev_zaps']
 [tests/functional/xattr]
 tests = ['xattr_001_pos', 'xattr_002_neg', 'xattr_003_neg', 'xattr_004_pos',
     'xattr_005_pos', 'xattr_006_pos', 'xattr_007_neg',
-    'xattr_011_pos', 'xattr_013_pos']
+    'xattr_011_pos', 'xattr_013_pos', 'xattr_compat']
 tags = ['functional', 'xattr']
 
 [tests/functional/zvol/zvol_ENOSPC]
diff --git a/tests/zfs-tests/include/tunables.cfg b/tests/zfs-tests/include/tunables.cfg
index fff43e469..eea2af2ed 100644
--- a/tests/zfs-tests/include/tunables.cfg
+++ b/tests/zfs-tests/include/tunables.cfg
@@ -87,6 +87,7 @@ VDEV_VALIDATE_SKIP		vdev.validate_skip		vdev_validate_skip
 VOL_INHIBIT_DEV			UNSUPPORTED			zvol_inhibit_dev
 VOL_MODE			vol.mode			zvol_volmode
 VOL_RECURSIVE			vol.recursive			UNSUPPORTED
+XATTR_COMPAT			xattr_compat			zfs_xattr_compat
 ZEVENT_LEN_MAX			zevent.len_max			zfs_zevent_len_max
 ZEVENT_RETAIN_MAX		zevent.retain_max		zfs_zevent_retain_max
 ZIO_SLOW_IO_MS			zio.slow_io_ms			zio_slow_io_ms
diff --git a/tests/zfs-tests/tests/functional/xattr/Makefile.am b/tests/zfs-tests/tests/functional/xattr/Makefile.am
index 17001885f..0cbd799aa 100644
--- a/tests/zfs-tests/tests/functional/xattr/Makefile.am
+++ b/tests/zfs-tests/tests/functional/xattr/Makefile.am
@@ -14,7 +14,8 @@ dist_pkgdata_SCRIPTS = \
 	xattr_010_neg.ksh \
 	xattr_011_pos.ksh \
 	xattr_012_pos.ksh \
-	xattr_013_pos.ksh
+	xattr_013_pos.ksh \
+	xattr_compat.ksh
 
 dist_pkgdata_DATA = \
 	xattr_common.kshlib \
diff --git a/tests/zfs-tests/tests/functional/xattr/xattr_compat.ksh b/tests/zfs-tests/tests/functional/xattr/xattr_compat.ksh
new file mode 100755
index 000000000..2f74ffe35
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/xattr/xattr_compat.ksh
@@ -0,0 +1,92 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# The contents of this file are subject to the terms of the
+# Common Development and Distribution License (the "License").
+# You may not use this file except in compliance with the License.
+#
+# You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+# or http://www.opensolaris.org/os/licensing.
+# See the License for the specific language governing permissions
+# and limitations under the License.
+#
+# When distributing Covered Code, include this CDDL HEADER in each
+# file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+# If applicable, add the following below this CDDL HEADER, with the
+# fields enclosed by brackets "[]" replaced with your own identifying
+# information: Portions Copyright [yyyy] [name of copyright owner]
+#
+# CDDL HEADER END
+#
+# Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
+# Use is subject to license terms.
+#
+
+#
+# Copyright 2022 iXsystems, Inc.
+#
+
+. $STF_SUITE/include/libtest.shlib
+
+#
+# DESCRIPTION:
+# The zfs_xattr_compat tunable and fallback works as expected.
+#
+# STRATEGY:
+#	For both of xattr=sa and xattr=dir:
+#	1. Create a filesystem with the native zfs_xattr_compat
+#	2. Create a file on the filesystem and add some xattrs to it
+#	3. Change the zfs_xattr_compat to the alternative setting
+#	4. Verify that the xattrs can still be accessed and modified
+#	5. Change zfs_xattr_compat back to the native setting
+#	6. Verify that the xattrs can still be accessed and modified
+#
+
+function cleanup {
+	rm -f $TESTFILE $TMPFILE
+	zfs set xattr=sa $TESTPOOL/$TESTFS
+	set_tunable32 XATTR_COMPAT $NATIVE_XATTR_COMPAT
+}
+
+log_assert "The zfs_xattr_compat tunable and fallback works as expected"
+log_onexit cleanup
+
+TESTFILE=$TESTDIR/testfile.$$
+TMPFILE=$TEST_BASE_DIR/tmpfile.$$
+NATIVE_XATTR_COMPAT=$(get_tunable XATTR_COMPAT)
+ALTERNATIVE_XATTR_COMPAT=$((1 - NATIVE_XATTR_COMPAT))
+
+for x in sa dir; do
+	log_must zfs set xattr=$x $TESTPOOL/$TESTFS
+	log_must touch $TESTFILE
+	log_must set_xattr testattr1 value1 $TESTFILE
+	log_must set_xattr testattr2 value2 $TESTFILE
+	log_must set_xattr testattr3 value3 $TESTFILE
+	log_must ls_xattr $TESTFILE
+
+	log_must set_tunable32 XATTR_COMPAT $ALTERNATIVE_XATTR_COMPAT
+	log_must ls_xattr $TESTFILE
+	log_must eval "get_xattr testattr1 $TESTFILE > $TMPFILE"
+	log_must test $(<$TMPFILE) = value1
+	log_must set_xattr testattr2 newvalue2 $TESTFILE
+	log_must rm_xattr testattr3 $TESTFILE
+	log_must set_xattr testattr4 value4 $TESTFILE
+	log_must ls_xattr $TESTFILE
+
+	log_must set_tunable32 XATTR_COMPAT $NATIVE_XATTR_COMPAT
+	log_must ls_xattr $TESTFILE
+	log_must eval "get_xattr testattr1 $TESTFILE > $TMPFILE"
+	log_must test $(<$TMPFILE) = value1
+	log_must eval "get_xattr testattr2 $TESTFILE > $TMPFILE"
+	log_must test $(<$TMPFILE) = newvalue2
+	log_mustnot get_xattr testattr3 $TESTFILE
+	log_must set_xattr testattr3 value3 $TESTFILE
+	log_must eval "get_xattr testattr4 $TESTFILE > $TMPFILE"
+	log_must test $(<$TMPFILE) = value4
+	log_must ls_xattr $TESTFILE
+
+	log_must rm $TESTFILE
+done
+
+log_pass "The zfs_xattr_compat tunable and fallback works as expected"