FreeBSD: Implement hole-punching support

This adds supports for hole-punching facilities in the FreeBSD kernel
starting from __FreeBSD_version 1400032.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Ka Ho Ng <khng@FreeBSD.org>
Sponsored-by: The FreeBSD Foundation
Closes #12458

module/os/freebsd/zfs/zfs_vnops_os.c

@@ -5237,6 +5237,11 @@ zfs_freebsd_pathconf(struct vop_pathconf_args *ap)
 	case _PC_NAME_MAX:
 		*ap->a_retval = NAME_MAX;
 		return (0);
+#if __FreeBSD_version >= 1400032
+	case _PC_DEALLOC_PRESENT:
+		*ap->a_retval = 1;
+		return (0);
+#endif
 	case _PC_PIPE_BUF:
 		if (ap->a_vp->v_type == VDIR || ap->a_vp->v_type == VFIFO) {
 			*ap->a_retval = PIPE_BUF;
@@ -6076,6 +6081,55 @@ zfs_vptocnp(struct vop_vptocnp_args *ap)
 	return (error);
 }
 
+#if __FreeBSD_version >= 1400032
+static int
+zfs_deallocate(struct vop_deallocate_args *ap)
+{
+	znode_t *zp = VTOZ(ap->a_vp);
+	zfsvfs_t *zfsvfs = zp->z_zfsvfs;
+	zilog_t *zilog;
+	off_t off, len, file_sz;
+	int error;
+
+	ZFS_ENTER(zfsvfs);
+	ZFS_VERIFY_ZP(zp);
+
+	/*
+	 * Callers might not be able to detect properly that we are read-only,
+	 * so check it explicitly here.
+	 */
+	if (zfs_is_readonly(zfsvfs)) {
+		ZFS_EXIT(zfsvfs);
+		return (SET_ERROR(EROFS));
+	}
+
+	zilog = zfsvfs->z_log;
+	off = *ap->a_offset;
+	len = *ap->a_len;
+	file_sz = zp->z_size;
+	if (off + len > file_sz)
+		len = file_sz - off;
+	/* Fast path for out-of-range request. */
+	if (len <= 0) {
+		*ap->a_len = 0;
+		ZFS_EXIT(zfsvfs);
+		return (0);
+	}
+
+	error = zfs_freesp(zp, off, len, O_RDWR, TRUE);
+	if (error == 0) {
+		if (zfsvfs->z_os->os_sync == ZFS_SYNC_ALWAYS ||
+		    (ap->a_ioflag & IO_SYNC) != 0)
+			zil_commit(zilog, zp->z_id);
+		*ap->a_offset = off + len;
+		*ap->a_len = 0;
+	}
+
+	ZFS_EXIT(zfsvfs);
+	return (error);
+}
+#endif
+
 struct vop_vector zfs_vnodeops;
 struct vop_vector zfs_fifoops;
 struct vop_vector zfs_shareops;
@@ -6095,6 +6149,9 @@ struct vop_vector zfs_vnodeops = {
 #endif
 	.vop_access =		zfs_freebsd_access,
 	.vop_allocate =		VOP_EINVAL,
+#if __FreeBSD_version >= 1400032
+	.vop_deallocate =	zfs_deallocate,
+#endif
 	.vop_lookup =		zfs_cache_lookup,
 	.vop_cachedlookup =	zfs_freebsd_cachedlookup,
 	.vop_getattr =		zfs_freebsd_getattr,

module/os/freebsd/zfs/zfs_znode.c

@@ -1487,12 +1487,16 @@ zfs_free_range(znode_t *zp, uint64_t off, uint64_t len)
 	error = dmu_free_long_range(zfsvfs->z_os, zp->z_id, off, len);
 
 	if (error == 0) {
+#if __FreeBSD_version >= 1400032
+		vnode_pager_purge_range(ZTOV(zp), off, off + len);
+#else
 		/*
-		 * In FreeBSD we cannot free block in the middle of a file,
-		 * but only at the end of a file, so this code path should
-		 * never happen.
+		 * Before __FreeBSD_version 1400032 we cannot free block in the
+		 * middle of a file, but only at the end of a file, so this code
+		 * path should never happen.
 		 */
 		vnode_pager_setsize(ZTOV(zp), off);
+#endif
 	}
 
 	zfs_rangelock_exit(lr);