qemu: add config parameter to control auto-save bypass cache

When doing managed save of VMs, triggered by OS shutdown, it may
be desirable to control cache usage.

Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

src/qemu/libvirtd_qemu.aug

@@ -107,6 +107,7 @@ module Libvirtd_qemu =
                  | str_entry "auto_shutdown_try_shutdown"
                  | str_entry "auto_shutdown_poweroff"
                  | int_entry "auto_shutdown_wait"
+                 | bool_entry "auto_save_bypass_cache"
 
    let process_entry = str_entry "hugetlbfs_mount"
                  | str_entry "bridge_helper"

src/qemu/qemu.conf.in

@@ -714,6 +714,14 @@
 # is currently 30 secs)
 #auto_shutdown_wait = 30
 
+# When a domain is configured to be auto-saved on shutdown, enabling
+# this flag has the same effect as using the VIR_DOMAIN_SAVE_BYPASS_CACHE
+# flag with the virDomainManagedSave API.  That is, the system will
+# avoid using the file system cache when writing any managed state
+# file, but may cause slower operation.
+#
+#auto_save_bypass_cache = 0
+
 # If provided by the host and a hugetlbfs mount point is configured,
 # a guest may request huge page backing.  When this mount point is
 # unspecified here, determination of a host mount point in /proc/mounts

src/qemu/qemu_conf.c

@@ -766,6 +766,9 @@ virQEMUDriverConfigLoadSaveEntry(virQEMUDriverConfig *cfg,
     if (virConfGetValueUInt(conf, "auto_shutdown_wait",
                             &cfg->autoShutdownWait) < 0)
         return -1;
+    if (virConfGetValueBool(conf, "auto_save_bypass_cache",
+                            &cfg->autoSaveBypassCache) < 0)
+        return -1;
 
     return 0;
 }

src/qemu/qemu_conf.h

@@ -216,6 +216,7 @@ struct _virQEMUDriverConfig {
     virDomainDriverAutoShutdownScope autoShutdownTryShutdown;
     virDomainDriverAutoShutdownScope autoShutdownPoweroff;
     unsigned int autoShutdownWait;
+    bool autoSaveBypassCache;
 
     char *lockManagerName;
 

src/qemu/qemu_driver.c

@@ -970,6 +970,7 @@ qemuStateStop(void)
         .tryShutdown = cfg->autoShutdownTryShutdown,
         .poweroff = cfg->autoShutdownPoweroff,
         .waitShutdownSecs = cfg->autoShutdownWait,
+        .saveBypassCache = cfg->autoSaveBypassCache,
     };
 
     virDomainDriverAutoShutdown(&ascfg);

src/qemu/test_libvirtd_qemu.aug.in

@@ -84,6 +84,7 @@ module Test_libvirtd_qemu =
 { "auto_shutdown_try_shutdown" = "all" }
 { "auto_shutdown_poweroff" = "all" }
 { "auto_shutdown_wait" = "30" }
+{ "auto_save_bypass_cache" = "0" }
 { "hugetlbfs_mount" = "/dev/hugepages" }
 { "bridge_helper" = "qemu-bridge-helper" }
 { "set_process_name" = "1" }