[libvirt PATCH 15/17] qemu: Add external_limit_manager config knob

[Andrea Bolognani]

This will be useful when libvirtd is running in a containerized
environment with limited capabilities, and in order to make
things like VFIO device assignment still work an external
privileged process changes the limits from outside of the
container. KubeVirt is an example of this setup.

Signed-off-by: Andrea Bolognani <abologna at redhat.com>
---
 src/qemu/libvirtd_qemu.aug         |  1 +
 src/qemu/qemu.conf                 | 12 ++++++++++++
 src/qemu/qemu_conf.c               |  4 ++++
 src/qemu/qemu_conf.h               |  1 +
 src/qemu/test_libvirtd_qemu.aug.in |  1 +
 5 files changed, 19 insertions(+)

diff --git a/src/qemu/libvirtd_qemu.aug b/src/qemu/libvirtd_qemu.aug
index 3c1045858b..f1b024a37f 100644
--- a/src/qemu/libvirtd_qemu.aug
+++ b/src/qemu/libvirtd_qemu.aug
@@ -104,6 +104,7 @@ module Libvirtd_qemu =
                  | str_entry "slirp_helper"
                  | str_entry "dbus_daemon"
                  | bool_entry "set_process_name"
+                 | bool_entry "external_limit_manager"
                  | int_entry "max_processes"
                  | int_entry "max_files"
                  | limits_entry "max_core"
diff --git a/src/qemu/qemu.conf b/src/qemu/qemu.conf
index 0c1054f198..15cbc3ba38 100644
--- a/src/qemu/qemu.conf
+++ b/src/qemu/qemu.conf
@@ -662,6 +662,18 @@
 #
 #set_process_name = 1
 
+# If enabled, libvirt will not attempt to change process limits (as
+# configured with the max_processes, max_files and max_core settings
+# below) itself but will instead expect an external entity to perform
+# this task.
+#
+# This also applies to the memory locking limit, which cannot be
+# configured here and is instead calculated dynamically based on the
+# exact guest configuration: if an external limit manager is in use,
+# then libvirt will merely check that the limit has been set
+# appropriately.
+#
+#external_limit_manager = 1
 
 # If max_processes is set to a positive integer, libvirt will use
 # it to set the maximum number of processes that can be run by qemu
diff --git a/src/qemu/qemu_conf.c b/src/qemu/qemu_conf.c
index 2bbc75024c..ee95c124dd 100644
--- a/src/qemu/qemu_conf.c
+++ b/src/qemu/qemu_conf.c
@@ -673,6 +673,10 @@ virQEMUDriverConfigLoadProcessEntry(virQEMUDriverConfigPtr cfg,
 
     if (virConfGetValueBool(conf, "set_process_name", &cfg->setProcessName) < 0)
         return -1;
+
+    if (virConfGetValueBool(conf, "external_limit_manager", &cfg->externalLimitManager) < 0)
+        return -1;
+
     if (virConfGetValueUInt(conf, "max_processes", &cfg->maxProcesses) < 0)
         return -1;
     if (virConfGetValueUInt(conf, "max_files", &cfg->maxFiles) < 0)
diff --git a/src/qemu/qemu_conf.h b/src/qemu/qemu_conf.h
index 7025b5222e..15e0353253 100644
--- a/src/qemu/qemu_conf.h
+++ b/src/qemu/qemu_conf.h
@@ -176,6 +176,7 @@ struct _virQEMUDriverConfig {
     bool nogfxAllowHostAudio;
     bool setProcessName;
 
+    bool externalLimitManager;
     unsigned int maxProcesses;
     unsigned int maxFiles;
     unsigned int maxThreadsPerProc;
diff --git a/src/qemu/test_libvirtd_qemu.aug.in b/src/qemu/test_libvirtd_qemu.aug.in
index 9310dcec1c..73be55febe 100644
--- a/src/qemu/test_libvirtd_qemu.aug.in
+++ b/src/qemu/test_libvirtd_qemu.aug.in
@@ -77,6 +77,7 @@ module Test_libvirtd_qemu =
 { "hugetlbfs_mount" = "/dev/hugepages" }
 { "bridge_helper" = "/usr/libexec/qemu-bridge-helper" }
 { "set_process_name" = "1" }
+{ "external_limit_manager" = "1" }
 { "max_processes" = "0" }
 { "max_files" = "0" }
 { "max_threads_per_process" = "0" }
-- 
2.26.2