[PATCH v4 2/2] tools/xenstore: set open file descriptor limit for xenstored

[Juergen Gross <jgross@xxxxxxxx>]

Add a configuration item for the maximum number of open file
descriptors xenstored should be allowed to have.

The default should be "unlimited" in order not to restrict xenstored
in the number of domains it can support, but unfortunately the prlimit
command requires specification of a real value for the number of files,
so use 262144 as the default value. As an aid for the admin configuring
the value add a comment specifying the common needs of xenstored for
the different domain types.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V2:
- set ulimit form launch script (Julien Grall)
- split off from original patch (Julien Grall)
V4:
- switch to directly configuring the limit of file descriptors instead
  of domains (Ian Jackson)
---
 tools/hotplug/Linux/init.d/sysconfig.xencommons.in | 13 +++++++++++++
 tools/hotplug/Linux/launch-xenstore.in             |  2 ++
 2 files changed, 15 insertions(+)

diff --git a/tools/hotplug/Linux/init.d/sysconfig.xencommons.in 
b/tools/hotplug/Linux/init.d/sysconfig.xencommons.in
index b83101ab7e..ad020b7a50 100644
--- a/tools/hotplug/Linux/init.d/sysconfig.xencommons.in
+++ b/tools/hotplug/Linux/init.d/sysconfig.xencommons.in
@@ -32,6 +32,19 @@
 # Changing this requires a reboot to take effect.
 #XENSTORED=@XENSTORED@
 
+## Type: integer
+## Default: 262144
+#
+# Select maximum number of file descriptors xenstored is allowed to have
+# opened at one time.
+# For each HVM domain xenstored might need up to 5 open file descriptors,
+# PVH and PV domains will require up to 3 open file descriptors. Additionally
+# 20-30 file descriptors will be opened for internal uses. The default of
+# 262144 allows for about 8 open files for the theoretical maximum of 32752
+# domains.
+# Only evaluated if XENSTORETYPE is "daemon".
+#XENSTORED_MAX_OPEN_FDS=262144
+
 ## Type: string
 ## Default: ""
 #
diff --git a/tools/hotplug/Linux/launch-xenstore.in 
b/tools/hotplug/Linux/launch-xenstore.in
index 1747c96065..2bc41bb4f0 100644
--- a/tools/hotplug/Linux/launch-xenstore.in
+++ b/tools/hotplug/Linux/launch-xenstore.in
@@ -54,6 +54,7 @@ test -f @CONFIG_DIR@/@CONFIG_LEAF_DIR@/xencommons && . 
@CONFIG_DIR@/@CONFIG_LEAF
 
 [ "$XENSTORETYPE" = "daemon" ] && {
        [ -z "$XENSTORED_TRACE" ] || XENSTORED_ARGS="$XENSTORED_ARGS -T 
@XEN_LOG_DIR@/xenstored-trace.log"
+       [ -z "$XENSTORED_MAX_OPEN_FDS" ] && XENSTORED_MAX_OPEN_FDS=262144
        [ -z "$XENSTORED" ] && XENSTORED=@XENSTORED@
        [ -x "$XENSTORED" ] || {
                echo "No xenstored found"
@@ -70,6 +71,7 @@ test -f @CONFIG_DIR@/@CONFIG_LEAF_DIR@/xencommons && . 
@CONFIG_DIR@/@CONFIG_LEAF
        systemd-notify --booted 2>/dev/null || timeout_xenstore $XENSTORED || 
exit 1
        XS_PID=`cat @XEN_RUN_DIR@/xenstored.pid`
        echo $XS_OOM_SCORE >/proc/$XS_PID/oom_score_adj
+       prlimit --pid $XS_PID --nofile=$XENSTORED_MAX_OPEN_FDS
 
        exit 0
 }
-- 
2.26.2