8940 Sending an intra-pool resumable send stream may result in EXDEV

illumos/illumos-gate@544132fce3fa6583f01318f9559adc46614343a7

"zfs send -t <token>" for an incremental send should be able to resume
successfully when sending to the same pool: a subtle issue in
zfs_iter_children() doesn't currently allow this.

Because resuming from a token requires "guid" -> "dataset" mapping
(guid_to_name()), we have to walk the whole hierarchy to find the right
snapshots to send.
When resuming an incremental send both source and destination live in the
same pool and have the same guid: this is where zfs_iter_children() gets
confused and picks up the wrong snapshot, so we end up trying to send an
incremental "destination@snap1 -> source@snap2" stream instead of
"source@snap1 -> source@snap2": this fails with an "Invalid cross-device
link" (EXDEV) error.

Reviewed by: Paul Dagnelie <pcd@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Hans Rosenfeld <rosenfeld@grumpf.hope-2000.org>
Author: loli10K <ezomori.nozomu@gmail.com>

2 files changed, 10 insertions, 5 deletions

diff --git a/lib/libzfs/common/libzfs_iter.c b/lib/libzfs/common/libzfs_iter.c
index f5ac68fc94e4..b0cb1ff18641 100644
--- a/lib/libzfs/common/libzfs_iter.c
+++ b/lib/libzfs/common/libzfs_iter.c
@@ -424,16 +424,20 @@ zfs_iter_snapspec(zfs_handle_t *fs_zhp, const char *spec_orig,
 
 /*
  * Iterate over all children, snapshots and filesystems
+ * Process snapshots before filesystems because they are nearer the input
+ * handle: this is extremely important when used with zfs_iter_f functions
+ * looking for data, following the logic that we would like to find it as soon
+ * and as close as possible.
  */
 int
 zfs_iter_children(zfs_handle_t *zhp, zfs_iter_f func, void *data)
 {
 	int ret;
 
-	if ((ret = zfs_iter_filesystems(zhp, func, data)) != 0)
+	if ((ret = zfs_iter_snapshots(zhp, B_FALSE, func, data)) != 0)
 		return (ret);
 
-	return (zfs_iter_snapshots(zhp, B_FALSE, func, data));
+	return (zfs_iter_filesystems(zhp, func, data));
 }
 
 
diff --git a/lib/libzfs/common/libzfs_sendrecv.c b/lib/libzfs/common/libzfs_sendrecv.c
index 4e89dc053d1d..d3002aec290a 100644
--- a/lib/libzfs/common/libzfs_sendrecv.c
+++ b/lib/libzfs/common/libzfs_sendrecv.c
@@ -1577,6 +1577,7 @@ zfs_send_resume(libzfs_handle_t *hdl, sendflags_t *flags, int outfd,
 	int error = 0;
 	char name[ZFS_MAX_DATASET_NAME_LEN];
 	enum lzc_send_flags lzc_flags = 0;
+	FILE *fout = (flags->verbose && flags->dryrun) ? stdout : stderr;
 
 	(void) snprintf(errbuf, sizeof (errbuf), dgettext(TEXT_DOMAIN,
 	    "cannot resume send"));
@@ -1591,9 +1592,9 @@ zfs_send_resume(libzfs_handle_t *hdl, sendflags_t *flags, int outfd,
 		return (zfs_error(hdl, EZFS_FAULT, errbuf));
 	}
 	if (flags->verbose) {
-		(void) fprintf(stderr, dgettext(TEXT_DOMAIN,
+		(void) fprintf(fout, dgettext(TEXT_DOMAIN,
 		    "resume token contents:\n"));
-		nvlist_print(stderr, resume_nvl);
+		nvlist_print(fout, resume_nvl);
 	}
 
 	if (nvlist_lookup_string(resume_nvl, "toname", &toname) != 0 ||
@@ -1650,7 +1651,7 @@ zfs_send_resume(libzfs_handle_t *hdl, sendflags_t *flags, int outfd,
 		    lzc_flags, &size);
 		if (error == 0)
 			size = MAX(0, (int64_t)(size - bytes));
-		send_print_verbose(stderr, zhp->zfs_name, fromname,
+		send_print_verbose(fout, zhp->zfs_name, fromname,
 		    size, flags->parsable);
 	}