OpenZFS 7541 - zpool import/tryimport ioctl returns ENOMEM

Authored by: Pavel Zakharov <[email protected]>
Reviewed by: Matthew Ahrens <[email protected]>
Reviewed by: Dan Kimmel <[email protected]>

The refresh_config() calls into the kernel with ZFS_IOC_POOL_TRYIMPORT.
This ioctl returns the config of the pool in a buffer pre-allocated in
userland. The original estimate for the size is too conservative since
it doesn't account for the large size of vdev stats that are added to
the config before returning.
This fix simply increases the size of the buffer passed. This results in
a speed up of the zpool import process, and less spam in zfs_dbgmsg.

Reviewed-by: Brian Behlendorf <[email protected]>
Ported-by: George Melikov <[email protected]>

OpenZFS-issue: https://www.illumos.org/issues/7541
OpenZFS-commit: openzfs/openzfs@a3c7690
Closes openzfs#5704

Author: gmelikov

include/libzfs_impl.h

@@ -131,6 +131,8 @@ typedef enum {
 	SHARED_SMB = 0x4
 } zfs_share_type_t;
 
+#define	CONFIG_BUF_MINSIZE	65536
+
 int zfs_error(libzfs_handle_t *, int, const char *);
 int zfs_error_fmt(libzfs_handle_t *, int, const char *, ...);
 void zfs_error_aux(libzfs_handle_t *, const char *, ...);

lib/libzfs/libzfs_import.c

@@ -21,7 +21,7 @@
 /*
  * Copyright 2015 Nexenta Systems, Inc. All rights reserved.
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2016 by Delphix. All rights reserved.
  * Copyright 2015 RackTop Systems.
  * Copyright (c) 2016, Intel Corporation.
  */
@@ -823,13 +823,14 @@ refresh_config(libzfs_handle_t *hdl, nvlist_t *config)
 {
 	nvlist_t *nvl;
 	zfs_cmd_t zc = {"\0"};
-	int err;
+	int err, dstbuf_size;
 
 	if (zcmd_write_conf_nvlist(hdl, &zc, config) != 0)
 		return (NULL);
 
-	if (zcmd_alloc_dst_nvlist(hdl, &zc,
-	    zc.zc_nvlist_conf_size * 2) != 0) {
+	dstbuf_size = MAX(CONFIG_BUF_MINSIZE, zc.zc_nvlist_conf_size * 4);
+
+	if (zcmd_alloc_dst_nvlist(hdl, &zc, dstbuf_size) != 0) {
 		zcmd_free_nvlists(&zc);
 		return (NULL);
 	}