install: re-check failed mkdir for EEXIST

Since the code stats and mkdirs in 2 separate steps, it is possible that
the directory will be created in the meantime by something else (e.g.
concurrent install).[1]

While here alter the code to properly report stat failure, previously it
would always claim it was mkdir which failed.

Noted by: royger [1]
MFC after:	1 week

1 files changed, 10 insertions, 5 deletions

diff --git a/usr.bin/xinstall/xinstall.c b/usr.bin/xinstall/xinstall.c
index f40cdc5..b59db70 100644
--- a/usr.bin/xinstall/xinstall.c
+++ b/usr.bin/xinstall/xinstall.c
@@ -1263,13 +1263,18 @@ install_dir(char *path)
 		if (!*p || (p != path && *p  == '/')) {
 			ch = *p;
 			*p = '\0';
-			if (stat(path, &sb)) {
-				if (errno != ENOENT || mkdir(path, 0755) < 0) {
+again:
+			if (stat(path, &sb) < 0) {
+				if (errno != ENOENT)
+					err(EX_OSERR, "stat %s", path);
+				if (mkdir(path, 0755) < 0) {
+					if (errno == EEXIST)
+						goto again;
 					err(EX_OSERR, "mkdir %s", path);
-					/* NOTREACHED */
-				} else if (verbose)
+				}
+				if (verbose)
 					(void)printf("install: mkdir %s\n",
-						     path);
+					    path);
 			} else if (!S_ISDIR(sb.st_mode))
 				errx(EX_OSERR, "%s exists but is not a directory", path);
 			if (!(*p = ch))