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

1 files changed, 3 insertions, 1 deletions

diff --git a/usr.bin/grep/util.c b/usr.bin/grep/util.c
index 33afe4d6b030..e517e4eaee6d 100644
--- a/usr.bin/grep/util.c
+++ b/usr.bin/grep/util.c
@@ -154,7 +154,7 @@ grep_tree(char **argv)
 	    __DECONST(char * const *, wd) : argv, fts_flags, NULL);
 	if (fts == NULL)
 		err(2, "fts_open");
-	while ((p = fts_read(fts)) != NULL) {
+	while (errno = 0, (p = fts_read(fts)) != NULL) {
 		switch (p->fts_info) {
 		case FTS_DNR:
 			/* FALLTHROUGH */
@@ -187,6 +187,8 @@ grep_tree(char **argv)
 			break;
 		}
 	}
+	if (errno != 0)
+		err(2, "fts_read");
 
 	fts_close(fts);
 	return (matched);