fts_read: Handle error from a NULL return better.

This is addressing cases such as fts_read(3) encountering an [EIO]
from fchdir(2) when FTS_NOCHDIR is not set.  That would otherwise be
seen as a successful traversal in some of these cases while silently
discarding expected work.

As noted in r264201, fts_read() does not set errno to 0 on a successful
EOF so it needs to be set before calling it.  Otherwise we might see
a random error from one of the iterations.

gzip is ignoring most errors and could be improved separately.

Reviewed by:	vangyzen
Sponsored by:	Dell EMC
Differential Revision:	https://reviews.freebsd.org/D27184

2 files changed, 6 insertions, 2 deletions

diff --git a/contrib/mtree/create.c b/contrib/mtree/create.c
index dc3af7447a39..7a09a1cc3951 100644
--- a/contrib/mtree/create.c
+++ b/contrib/mtree/create.c
@@ -129,7 +129,7 @@ cwalk(FILE *fp)
 
 	if ((t = fts_open(argv, ftsoptions, dcmp)) == NULL)
 		mtree_err("fts_open: %s", strerror(errno));
-	while ((p = fts_read(t)) != NULL) {
+	while (errno = 0, (p = fts_read(t)) != NULL) {
 		if (jflag)
 			indent = p->fts_level * 4;
 		if (check_excludes(p->fts_name, p->fts_path)) {
@@ -173,6 +173,8 @@ cwalk(FILE *fp)
 
 		}
 	}
+	if (errno != 0)
+		mtree_err("fts_read: %s", strerror(errno));
 	fts_close(t);
 	if (sflag && keys & F_CKSUM)
 		mtree_err("%s checksum: %u", fullpath, crc_total);
diff --git a/contrib/mtree/verify.c b/contrib/mtree/verify.c
index 66b020ac8b9f..4aca42c52aea 100644
--- a/contrib/mtree/verify.c
+++ b/contrib/mtree/verify.c
@@ -90,7 +90,7 @@ vwalk(void)
 		mtree_err("fts_open: %s", strerror(errno));
 	level = root;
 	specdepth = rval = 0;
-	while ((p = fts_read(t)) != NULL) {
+	while (errno = 0, (p = fts_read(t)) != NULL) {
 		if (check_excludes(p->fts_name, p->fts_path)) {
 			fts_set(t, p, FTS_SKIP);
 			continue;
@@ -160,6 +160,8 @@ vwalk(void)
 		}
 		fts_set(t, p, FTS_SKIP);
 	}
+	if (errno != 0)
+		mtree_err("fts_read: %s", strerror(errno));
 	fts_close(t);
 	if (sflag)
 		warnx("%s checksum: %u", fullpath, crc_total);