receive ioctl should check unsupported features

When receiving a send stream that has unexpected features enabled (i.e.
a flag is set in `DMU_GET_FEATUREFLAGS(drr_versioninfo)` that is not in
`DMU_BACKUP_FEATURE_MASK`), libzfs will detect this and fail, printing
`cannot receive: stream has unsupported feature, feature flags = ...`.

However, if a process is using libzfs_core directly (i.e.
`lzc_receive*()`), or if libzfs and the kernel module are mismatched,
then the kernel may attempt to receive a stream with unsupported
features.

The problem is that the kernel is not explicitly checking
drr_versioninfo for unsupported features.  Typically this will cause the
receive the fail with EINVAL when it encounters a specific piece of
metadata that is not understood (e.g. a new record type).  However,
other, arbitrarily bad failure modes are also possible.

The solution is to make the kernel explicitly check drr_versioninfo for
unsupported features.  A new zfs_errno_t value was added, which the
kernel will return, and libzfs will print `cannot receive new filesystem
stream: the loaded zfs module does not support this operation. A reboot
may be required to enable this operation.`

Author: ahrens

include/sys/fs/zfs.h

@@ -1224,6 +1224,7 @@ typedef enum {
 	ZFS_ERR_IOC_ARG_UNAVAIL,
 	ZFS_ERR_IOC_ARG_REQUIRED,
 	ZFS_ERR_IOC_ARG_BADTYPE,
+	ZFS_ERR_UNKNOWN_SEND_STREAM_FEATURE,
 } zfs_errno_t;
 
 /*

lib/libzfs/libzfs_util.c

@@ -450,6 +450,7 @@ zfs_standard_error_fmt(libzfs_handle_t *hdl, int error, const char *fmt, ...)
 	case EREMOTEIO:
 		zfs_verror(hdl, EZFS_ACTIVE_POOL, fmt, ap);
 		break;
+	case ZFS_ERR_UNKNOWN_SEND_STREAM_FEATURE:
 	case ZFS_ERR_IOC_CMD_UNAVAIL:
 		zfs_error_aux(hdl, dgettext(TEXT_DOMAIN, "the loaded zfs "
 		    "module does not support this operation. A reboot may "

module/zfs/dmu_recv.c

@@ -476,6 +476,13 @@ recv_begin_check_existing_impl(dmu_recv_begin_arg_t *drba, dsl_dataset_t *ds,
 static int
 recv_begin_check_feature_flags_impl(uint64_t featureflags, spa_t *spa)
 {
+	/*
+	 * Check if there are any unsupported feature flags.
+	 */
+	if (!DMU_STREAM_SUPPORTED(featureflags)) {
+		return (SET_ERROR(ZFS_ERR_UNKNOWN_SEND_STREAM_FEATURE));
+	}
+
 	/* Verify pool version supports SA if SA_SPILL feature set */
 	if ((featureflags & DMU_BACKUP_FEATURE_SA_SPILL) &&
 	    spa_version(spa) < SPA_VERSION_SA)