mkdumprd: use 300s as the default systemd unit timeout for kdump mount

Currently, systemd uses 90s as the default mount unit timeout
(see "man 5 systemd-system.conf " for "DefaultTimeoutStartSec"),
in some cases, although it works well in 1st kernel, it's not
enough under kdump and results in mount timeout, further results
in kdump dumping failure.

We've met several such issues, we decided to enlarge this default
value a little for kdump.

We know that dracut has a default initqueue timeout value of 180s
("rd.retry"), we finalized a little larger value 300s as kdump's
default timeout if there is no explicit "DefaultTimeoutStartSec=X,
specified by users.

"DefaultTimeoutStartSec=X" can be overridden by individual mount
option "x-systemd.device-timeout=X", users can specify their own
values as needed.

This patch achieves the purpose by creating a dedicated conf file
"/etc/systemd/system.conf.d/kdump.conf" which has the content of
"DefaultTimeoutStartSec=300s", this is based on the fact that all
the conf files will be parsed by systemd and the last parsed one
will be used if there are duplicate definitions.

Signed-off-by: Xunlei Pang <xlpang@redhat.com>
Acked-by: Dave Young <dyoung@redhat.com>

dracut-module-setup.sh

@@ -753,4 +753,13 @@ install() {
     sed -i -e \
       's/\(^[[:space:]]*reserved_memory[[:space:]]*=\)[[:space:]]*[[:digit:]]*/\1 1024/' \
       ${initdir}/etc/lvm/lvm.conf &>/dev/null
+
+    # Kdump turns out to require longer default systemd mount timeout
+    # than 1st kernel(90s by default), we use default 300s for kdump.
+    grep -r "^[[:space:]]*DefaultTimeoutStartSec=" ${initdir}/etc/systemd/system.conf* &>/dev/null
+    if [ $? -ne 0 ]; then
+        mkdir -p ${initdir}/etc/systemd/system.conf.d
+        echo "[Manager]" > ${initdir}/etc/systemd/system.conf.d/kdump.conf
+        echo "DefaultTimeoutStartSec=300s" >> ${initdir}/etc/systemd/system.conf.d/kdump.conf
+    fi
 }