WIP xattr_compat for FreeBSD

include/os/freebsd/zfs/sys/zfs_vfsops_os.h

@@ -240,7 +240,9 @@ struct zfsvfs {
 	RW_WRITE_HELD(&(zfsvfs)->z_teardown_inactive_lock)
 #endif
 
-#define	ZSB_XATTR	0x0001		/* Enable user xattrs */
+#define	ZSB_XATTR		0x0001	/* Enable user xattrs */
+#define	ZSB_XATTR_COMPAT	0x0002	/* Enable cross-platform user xattrs */
+
 /*
  * Normal filesystems (those not under .zfs/snapshot) have a total
  * file ID size limited to 12 bytes (including the length field) due to

module/os/freebsd/zfs/zfs_vfsops.c

@@ -56,6 +56,7 @@
 #include <sys/sa_impl.h>
 #include <sys/policy.h>
 #include <sys/atomic.h>
+#include <sys/zfeature.h>
 #include <sys/zfs_ioctl.h>
 #include <sys/zfs_ctldir.h>
 #include <sys/zfs_fuid.h>
@@ -478,6 +479,31 @@ xattr_changed_cb(void *arg, uint64_t newval)
 	}
 }
 
+static void
+xattr_compat_changed_cb(void *arg, uint64_t newval)
+{
+	zfsvfs_t *zfsvfs = arg;
+
+	/*
+	 *  Force the old cross-platform compatible behavior if
+	 *  feature@xattr_compat is disabled.  This contrasts with
+	 *  Linux where the behavior prior to feature@xattr_compat
+	 *  was to use the incompatible Linux-only xattr format.
+	 */
+	if (!spa_feature_is_enabled(dmu_objset_spa(zfsvfs->z_os),
+	    SPA_FEATURE_XATTR_COMPAT))
+		newval = ZFS_XATTR_COMPAT_ALL;
+
+	switch (newval) {
+	case ZFS_XATTR_COMPAT_ALL:
+		zfsvfs->z_flags |= ZSB_XATTR_COMPAT;
+		break;
+	case ZFS_XATTR_COMPAT_LINUX:
+		zfsvfs->z_flags &= ~ZSB_XATTR_COMPAT;
+		break;
+	}
+}
+
 static void
 blksz_changed_cb(void *arg, uint64_t newval)
 {
@@ -721,6 +747,9 @@ zfs_register_callbacks(vfs_t *vfsp)
 	    zfs_prop_to_name(ZFS_PROP_ATIME), atime_changed_cb, zfsvfs);
 	error = error ? error : dsl_prop_register(ds,
 	    zfs_prop_to_name(ZFS_PROP_XATTR), xattr_changed_cb, zfsvfs);
+	error = error ? error : dsl_prop_register(ds,
+	    zfs_prop_to_name(ZFS_PROP_XATTR_COMPAT), xattr_compat_changed_cb,
+	    zfsvfs);
 	error = error ? error : dsl_prop_register(ds,
 	    zfs_prop_to_name(ZFS_PROP_RECORDSIZE), blksz_changed_cb, zfsvfs);
 	error = error ? error : dsl_prop_register(ds,
@@ -1237,6 +1266,10 @@ zfs_domount(vfs_t *vfsp, char *osname)
 		    "xattr", &pval, NULL)))
 			goto out;
 		xattr_changed_cb(zfsvfs, pval);
+		if ((error = dsl_prop_get_integer(osname,
+		    "xattr_compat", &pval, NULL)))
+			goto out;
+		xattr_compat_changed_cb(zfsvfs, pval);
 		if ((error = dsl_prop_get_integer(osname,
 		    "acltype", &pval, NULL)))
 			goto out;