[PATCH 2 of 2] Lowmemd: Simple demo code to show use of VIRQ_ENOMEM

[Andres Lagar-Cavilla <andres@lagarcavilla.org>]

 .gitignore               |    1 +
 .hgignore                |    1 +
 tools/misc/Makefile      |    7 +-
 tools/misc/xen-lowmemd.c |  148 +++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 155 insertions(+), 2 deletions(-)


Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

diff -r 8938a0111344 -r 95417b1a745d .gitignore
--- a/.gitignore
+++ b/.gitignore
@@ -197,6 +197,7 @@ tools/misc/xen-hvmctx
 tools/misc/gtraceview
 tools/misc/gtracestat
 tools/misc/xenlockprof
+tools/misc/lowmemd
 tools/pygrub/build/*
 tools/python/build/*
 tools/python/xen/util/path.py
diff -r 8938a0111344 -r 95417b1a745d .hgignore
--- a/.hgignore
+++ b/.hgignore
@@ -202,6 +202,7 @@
 ^tools/misc/xenperf$
 ^tools/misc/xenpm$
 ^tools/misc/xen-hvmctx$
+^tools/misc/xen-lowmemd$
 ^tools/misc/gtraceview$
 ^tools/misc/gtracestat$
 ^tools/misc/xenlockprof$
diff -r 8938a0111344 -r 95417b1a745d tools/misc/Makefile
--- a/tools/misc/Makefile
+++ b/tools/misc/Makefile
@@ -9,7 +9,7 @@ CFLAGS += $(CFLAGS_xeninclude)
 HDRS     = $(wildcard *.h)
 
 TARGETS-y := xenperf xenpm xen-tmem-list-parse gtraceview gtracestat xenlockprof xenwatchdogd
-TARGETS-$(CONFIG_X86) += xen-detect xen-hvmctx xen-hvmcrash
+TARGETS-$(CONFIG_X86) += xen-detect xen-hvmctx xen-hvmcrash xen-lowmemd
 TARGETS-$(CONFIG_MIGRATE) += xen-hptool
 TARGETS := $(TARGETS-y)
 
@@ -21,7 +21,7 @@ INSTALL_BIN-y := xencons
 INSTALL_BIN-$(CONFIG_X86) += xen-detect
 INSTALL_BIN := $(INSTALL_BIN-y)
 
-INSTALL_SBIN-y := xm xen-bugtool xen-python-path xend xenperf xsview xenpm xen-tmem-list-parse gtraceview gtracestat xenlockprof xenwatchdogd xen-ringwatch
+INSTALL_SBIN-y := xm xen-bugtool xen-python-path xend xenperf xsview xenpm xen-tmem-list-parse gtraceview gtracestat xenlockprof xenwatchdogd xen-ringwatch xen-lowmemd
 INSTALL_SBIN-$(CONFIG_X86) += xen-hvmctx xen-hvmcrash
 INSTALL_SBIN-$(CONFIG_MIGRATE) += xen-hptool
 INSTALL_SBIN := $(INSTALL_SBIN-y)
@@ -70,6 +70,9 @@ xen-hptool: xen-hptool.o
 xenwatchdogd: xenwatchdogd.o
 	$(CC) $(LDFLAGS) -o $@ $< $(LDLIBS_libxenctrl) $(APPEND_LDFLAGS)
 
+xen-lowmemd: xen-lowmemd.o
+	$(CC) $(LDFLAGS) -o $@ $< $(LDLIBS_libxenctrl) $(LDLIBS_libxenstore) $(APPEND_LDFLAGS)
+
 gtraceview: gtraceview.o
 	$(CC) $(LDFLAGS) -o $@ $< $(CURSES_LIBS) $(APPEND_LDFLAGS)
 
diff -r 8938a0111344 -r 95417b1a745d tools/misc/xen-lowmemd.c
--- /dev/null
+++ b/tools/misc/xen-lowmemd.c
@@ -0,0 +1,148 @@
+/*
+ * xen-lowmemd: demo VIRQ_ENOMEM
+ * Andres Lagar-Cavilla (GridCentric Inc.)
+ */
+
+#include <stdio.h>
+#include <xenctrl.h>
+#include <xs.h>
+#include <stdlib.h>
+#include <string.h>
+
+static evtchn_port_t virq_port      = -1;
+static xc_evtchn *xce_handle        = NULL;
+static xc_interface *xch            = NULL;
+static struct xs_handle *xs_handle  = NULL;
+
+void cleanup(void)
+{
+    if (virq_port > -1)
+        xc_evtchn_unbind(xce_handle, virq_port);
+    if (xce_handle)
+        xc_evtchn_close(xce_handle);
+    if (xch)
+        xc_interface_close(xch);
+    if (xs_handle)
+        xs_daemon_close(xs_handle);
+}
+
+/* Never shrink dom0 below 1 GiB */
+#define DOM0_FLOOR  (1 << 30)
+#define DOM0_FLOOR_PG   ((DOM0_FLOOR) >> 12)
+
+/* Act if free memory is less than 92 MiB */
+#define THRESHOLD   (92 << 20)
+#define THRESHOLD_PG    ((THRESHOLD) >> 12)
+
+#define BUFSZ 512
+void handle_low_mem(void)
+{
+    xc_dominfo_t  dom0_info;
+    xc_physinfo_t info;
+    unsigned long long free_pages, dom0_pages, diff, dom0_target;
+    char data[BUFSZ], error[BUFSZ];
+
+    if (xc_physinfo(xch, &info) < 0)
+    {
+        perror("Getting physinfo failed");
+        return;
+    }
+
+    free_pages = (unsigned long long) info.free_pages;
+    printf("Available free pages: 0x%llx:%llux\n",
+            free_pages, free_pages);
+
+    /* Don't do anything if we have more than the threshold free */
+    if ( free_pages >= THRESHOLD_PG )
+        return;
+    diff = THRESHOLD_PG - free_pages; 
+
+    if (xc_domain_getinfo(xch, 0, 1, &dom0_info) < 1)
+    {
+        perror("Failed to get dom0 info");
+        return;
+    }
+
+    dom0_pages = (unsigned long long) dom0_info.nr_pages;
+    printf("Dom0 pages: 0x%llx:%llu\n", dom0_pages, dom0_pages);
+    dom0_target = dom0_pages - diff;
+    if (dom0_target <= DOM0_FLOOR_PG)
+        return;
+
+    printf("Shooting for dom0 target 0x%llx:%llu\n", 
+            dom0_target, dom0_target);
+
+    snprintf(data, BUFSZ, "%llu", dom0_target);
+    if (!xs_write(xs_handle, XBT_NULL, 
+            "/local/domain/0/memory/target", data, strlen(data)))
+    {
+        snprintf(error, BUFSZ,"Failed to write target %s to xenstore", data);
+        perror(error);
+    }
+}
+
+int main(int argc, char *argv[])
+{
+    int rc;
+
+    atexit(cleanup);
+
+	xch = xc_interface_open(NULL, NULL, 0);
+	if (xch == NULL)
+    {
+        perror("Failed to open xc interface");
+        return 1;
+    }
+
+	xce_handle = xc_evtchn_open(NULL, 0);
+	if (xce_handle == NULL)
+    {
+        perror("Failed to open evtchn device");
+        return 2;
+    }
+
+    xs_handle = xs_daemon_open();
+    if (xs_handle == NULL)
+    {
+        perror("Failed to open xenstore connection");
+        return 3;
+    }
+
+	if ((rc = xc_evtchn_bind_virq(xce_handle, VIRQ_ENOMEM)) == -1)
+    {
+        perror("Failed to bind to domain exception virq port");
+        return 4;
+    }
+
+    virq_port = rc;
+    
+    while(1)
+    {
+        evtchn_port_t port;
+
+        if ((port = xc_evtchn_pending(xce_handle)) == -1)
+        {
+            perror("Failed to listen for pending event channel");
+            return 5;
+        }
+
+        if (port != virq_port)
+        {
+            char data[BUFSZ];
+            snprintf(data, BUFSZ, "Wrong port, got %d expected %d", port, virq_port);
+            perror(data);
+            return 6;
+        }
+
+        if (xc_evtchn_unmask(xce_handle, port) == -1)
+        {
+            perror("Failed to unmask port");
+            return 7;
+        }
+
+        printf("Got a virq kick, time to get work\n");
+        handle_low_mem();
+    }
+
+    return 0;
+}