xen: add kconfig for event_fifo

Commit Message

Stefano Stabellini March 18, 2025, 11:40 p.m. UTC

Evtchn fifos are not needed on smaller systems; the older interface is
lightweight and sufficient. Make it possible to disable evtchn fifo.

Signed-off-by: Stefano Stabellini <[e-mail]>

Patch

diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index a6aa2c5c14..14d82923c5 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -23,6 +23,16 @@  config GRANT_TABLE
 
 	  If unsure, say Y.
 
+config EVTCHN_FIFO
+	bool "Event Channel Fifo support" if EXPERT
+	default y
+	help
+	  The Event channel Fifo extends support for event channels
+	  beyond 1024 event channels for 32-bit guests and 4096 for
+	  64-bit guests.
+
+	  If unsure, say Y.
+
 config PDX_COMPRESSION
 	bool "PDX (Page inDeX) compression" if EXPERT && !X86 && !RISCV
 	default ARM || PPC
diff --git a/xen/common/Makefile b/xen/common/Makefile
index ac23120d7d..9da8a7244d 100644
--- a/xen/common/Makefile
+++ b/xen/common/Makefile
@@ -13,7 +13,7 @@  obj-$(CONFIG_IOREQ_SERVER) += dm.o
 obj-y += domain.o
 obj-y += event_2l.o
 obj-y += event_channel.o
-obj-y += event_fifo.o
+obj-$(CONFIG_EVTCHN_FIFO) += event_fifo.o
 obj-$(CONFIG_GRANT_TABLE) += grant_table.o
 obj-y += guestcopy.o
 obj-y += gzip/
diff --git a/xen/common/event_channel.h b/xen/common/event_channel.h
index 45219ca67c..a778ae775b 100644
--- a/xen/common/event_channel.h
+++ b/xen/common/event_channel.h
@@ -45,12 +45,27 @@  void evtchn_2l_init(struct domain *d);
 
 /* FIFO */
 
+#ifdef CONFIG_EVTCHN_FIFO
 struct evtchn_init_control;
 struct evtchn_expand_array;
 
 int evtchn_fifo_init_control(struct evtchn_init_control *init_control);
 int evtchn_fifo_expand_array(const struct evtchn_expand_array *expand_array);
 void evtchn_fifo_destroy(struct domain *d);
+#else
+static inline int evtchn_fifo_init_control(struct evtchn_init_control *init_control)
+{
+    return -EOPNOTSUPP;
+}
+static inline int evtchn_fifo_expand_array(const struct evtchn_expand_array *expand_array)
+{
+    return -EOPNOTSUPP;
+}
+static inline void evtchn_fifo_destroy(struct domain *d)
+{
+    return;
+}
+#endif /* CONFIG_EVTCHN_FIFO */
 
 /*
  * Local variables: