[PATCH 11/11] libxl, xl: add event_channels option to xl configuration file

[David Vrabel <david.vrabel@citrix.com>]

From: David Vrabel <david.vrabel@citrix.com>

Add the 'event_channels' option to the xl configuration file to limit
the number of event channels that domain may use.

Plumb this option through to libxl via a new libxl_build_info field
and call xc_domain_set_max_evtchn() in the post build stage of domain
creation.

A new LIBXL_HAVE_BUILDINFO_EVENT_CHANNELS #define indicates that this
new field is available.

The default value of 127 limits the domain to uses the minimum amount
of Xen resources (xenheap and global mapping pages) regardless of
event channel ABI that may be used by a guest.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
---
 docs/man/xl.cfg.pod.5       |   12 ++++++++++++
 tools/libxl/libxl.h         |    5 +++++
 tools/libxl/libxl_create.c  |    3 +++
 tools/libxl/libxl_dom.c     |    4 ++++
 tools/libxl/libxl_types.idl |    1 +
 tools/libxl/xl_cmdimpl.c    |    3 +++
 6 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
index 769767b..3c7dd28 100644
--- a/docs/man/xl.cfg.pod.5
+++ b/docs/man/xl.cfg.pod.5
@@ -572,6 +572,18 @@ Allow a guest to access specific physical IRQs.
 It is recommended to use this option only for trusted VMs under
 administrator control.
 
+=item B<event_channels=N>
+
+Limit the guest to using a most N event channels (PV interrupts).
+Guests use hypervisor resources for each event channel they use.
+
+The default of 127 should be sufficient for typical guests and means
+the guest uses the lowest amout of hypervisor resources.  The maximum
+value depends what the guest supports.  Guests supporting the
+FIFO-based event channel ABI support up to 131,071 event channels.
+Other guests are limited to 4095 (64-bit x86 and ARM) or 1023 (32-bit
+x86).
+
 =back
 
 =head2 Paravirtualised (PV) Guest Specific Options
diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index 4cab294..30712c2 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -90,6 +90,11 @@
 #define LIBXL_HAVE_BUILDINFO_HVM_VENDOR_DEVICE 1
 
 /*
+ * The libxl_domain_build_info has the event_channels field.
+ */
+#define LIBXL_HAVE_BUILDINFO_EVENT_CHANNELS 1
+
+/*
  * libxl ABI compatibility
  *
  * The only guarantee which libxl makes regarding ABI compatibility
diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 7567238..806e25c 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -208,6 +208,9 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
 
     libxl_defbool_setdefault(&b_info->disable_migrate, false);
 
+    if (!b_info->event_channels)
+        b_info->event_channels = 127;
+
     switch (b_info->type) {
     case LIBXL_DOMAIN_TYPE_HVM:
         if (b_info->shadow_memkb == LIBXL_MEMKB_DEFAULT)
diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
index 6e2252a..c905c74 100644
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -268,6 +268,10 @@ int libxl__build_post(libxl__gc *gc, uint32_t domid,
     if (rc)
         return rc;
 
+    rc = xc_domain_set_max_evtchn(ctx->xch, domid, info->event_channels);
+    if (rc)
+        return rc;
+
     libxl_cpuid_apply_policy(ctx, domid);
     if (info->cpuid != NULL)
         libxl_cpuid_set(ctx, domid, info->cpuid);
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 049dbb5..7bf517d 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -308,6 +308,7 @@ libxl_domain_build_info = Struct("domain_build_info",[
     ("irqs",             Array(uint32, "num_irqs")),
     ("iomem",            Array(libxl_iomem_range, "num_iomem")),
     ("claim_mode",	     libxl_defbool),
+    ("event_channels",   uint32),
     ("u", KeyedUnion(None, libxl_domain_type, "type",
                 [("hvm", Struct(None, [("firmware",         string),
                                        ("bios",             libxl_bios_type),
diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index 3d7eaad..7931bb9 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -813,6 +813,9 @@ static void parse_config_data(const char *config_source,
     if (!xlu_cfg_get_long (config, "videoram", &l, 0))
         b_info->video_memkb = l * 1024;
 
+    if (!xlu_cfg_get_long(config, "event_channels", &l, 0))
+        b_info->event_channels = l;
+
     switch(b_info->type) {
     case LIBXL_DOMAIN_TYPE_HVM:
         if (!xlu_cfg_get_string (config, "kernel", &buf, 0))
-- 
1.7.2.5