tests: read limited amount from /dev/urandom

In some test environments like e.g. Ubuntu & Debian autopkgtest it
can happen that while generating random device names the pipes
between tr and head are considered dead while processing.
That prints (non fatal) issues like:
  Running ip/link/new_link.t [iproute2-this/4.13.0-17-generic]: tr:
write error: Broken pipe
  tr: write error
  PASS

This only happens if reading an infinite amount of chars with the
read from urandom, so reading a defined amount fixes the issue.

Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

diff --git a/testsuite/lib/generic.sh b/testsuite/lib/generic.sh
index b7de70441dd280147e852ef7aec2fc18b3d79537..3645ff52dcbbc556965d44f73f193b16321efd91 100644 (file)
--- a/testsuite/lib/generic.sh
+++ b/testsuite/lib/generic.sh
@@ -87,7 +87,7 @@ ts_qdisc_available()
 
 rand_dev()
 {
-    echo "dev-$(tr -dc "[:alpha:]" < /dev/urandom | head -c 6)"
+    echo "dev-$(head -c 250 /dev/urandom | tr -dc '[:alpha:]' | head -c 6)"
 }
 
 pr_failed()