libxl: populate xenstore memory entries at startup, handle dom0_mem

libxl uses some xenstore entries for hints in memory management
(especially when starting new domain). This includes dom0 memory limit
and Xen free memory margin, based on current system state. Entries are
created at first function usage, so force such call at daemon startup,
which most likely will be before any domain startup.
Also prevent automatic memory management if dom0_mem= option passed to
xen hypervisor - it is known to be incompatible with autoballoon.
Signed-off-by: NMarek Marczykowski-Górecki <marmarek@invisiblethingslab.com>

src/libxl/libxl_conf.h

@@ -63,6 +63,10 @@ struct _libxlDriverPrivate {
 
     virPortAllocatorPtr reservedVNCPorts;
 
+    /* Controls automatic ballooning of domain0. If true, attempt to get
+     * memory for new domains from domain0. */
+    bool autoballoon;
+
     size_t nactive;
     virStateInhibitCallback inhibitCallback;
     void *inhibitOpaque;

src/libxl/libxl_driver.c

@@ -29,6 +29,7 @@
 #include <math.h>
 #include <libxl.h>
 #include <fcntl.h>
+#include <regex.h>
 
 #include "internal.h"
 #include "virlog.h"
@@ -978,7 +979,7 @@ libxlVmStart(libxlDriverPrivatePtr driver, virDomainObjPtr vm,
     if (libxlBuildDomainConfig(driver, vm->def, &d_config) < 0)
         goto error;
 
-    if (libxlFreeMem(priv, &d_config) < 0) {
+    if (driver->autoballoon && libxlFreeMem(priv, &d_config) < 0) {
         virReportError(VIR_ERR_INTERNAL_ERROR,
                        _("libxenlight failed to get free memory for domain '%s'"),
                        d_config.c_info.name);
@@ -1160,6 +1161,29 @@ libxlStateCleanup(void)
     return 0;
 }
 
+static bool
+libxlGetAutoballoon(libxlDriverPrivatePtr driver)
+{
+    const libxl_version_info *info;
+    regex_t regex;
+    int ret;
+
+    info = libxl_get_version_info(driver->ctx);
+    if (!info)
+        return true; /* default to on */
+
+    ret = regcomp(&regex,
+            "(^| )dom0_mem=((|min:|max:)[0-9]+[bBkKmMgG]?,?)+($| )",
+            REG_NOSUB | REG_EXTENDED);
+    if (ret)
+        return true;
+
+    ret = regexec(&regex, info->commandline, 0, NULL, 0);
+    regfree(&regex);
+    return ret == REG_NOMATCH;
+}
+
+
 static int
 libxlStateInitialize(bool privileged,
                      virStateInhibitCallback callback ATTRIBUTE_UNUSED,
@@ -1169,6 +1193,7 @@ libxlStateInitialize(bool privileged,
     char *log_file = NULL;
     virCommandPtr cmd;
     int status, ret = 0;
+    unsigned int free_mem;
     char ebuf[1024];
 
     /* Disable libxl driver if non-root */
@@ -1293,6 +1318,16 @@ libxlStateInitialize(bool privileged,
                                                        NULL)))
         goto error;
 
+    /* This will fill xenstore info about free and dom0 memory if missing,
+     * should be called before starting first domain */
+    if (libxl_get_free_memory(libxl_driver->ctx, &free_mem)) {
+        VIR_ERROR(_("Unable to configure libxl's memory management parameters"));
+        goto error;
+    }
+
+    /* setup autoballoon */
+    libxl_driver->autoballoon = libxlGetAutoballoon(libxl_driver);
+
     /* Load running domains first. */
     if (virDomainObjListLoadAllConfigs(libxl_driver->domains,
                                        libxl_driver->stateDir,