vefd: Thin wrapper around eventfd with pipe emulation

configure.ac

@@ -483,6 +483,8 @@ else
 	ac_cv_func_port_create=no
 fi
 
+AC_CHECK_FUNCS([eventfd])
+
 # --with-persistent-storage
 AC_ARG_WITH(persistent-storage,
     AS_HELP_STRING([--with-persistent-storage],

include/Makefile.am

@@ -95,6 +95,7 @@ nobase_noinst_HEADERS = \
 	vcs_version.h \
 	vct.h \
 	vcurses.h \
+	vefd.h \
 	venc.h \
 	vend.h \
 	vev.h \

include/vefd.h

@@ -0,0 +1,50 @@
+/*-
+ * Copyright (c) 2025 Varnish Software AS
+ * All rights reserved.
+ *
+ * Author: Dridi Boukelmoune <[email protected]>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer
+ *    in this position and unchanged.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ */
+
+struct vefd {
+	unsigned	magic;
+#define VEFD_MAGIC	0x1548c1a6
+	int		poll_fd;
+	int		priv_fd;
+};
+
+#define VEFD_INIT(vefd)				\
+	do {					\
+		INIT_OBJ(vefd, VEFD_MAGIC);	\
+		(vefd)->poll_fd = -1;		\
+		(vefd)->priv_fd = -1;		\
+	} while (0)
+
+int VEFD_Open(struct vefd *);
+int VEFD_Signal(struct vefd *);
+int VEFD_Clear(struct vefd *);
+int VEFD_Close(struct vefd *);

lib/libvarnish/Makefile.am

@@ -23,6 +23,7 @@ libvarnish_la_SOURCES = \
 	vcli_serve.c \
 	vct.c \
 	venc.c \
+	vefd.c \
 	version.c \
 	vev.c \
 	vfil.c \

lib/libvarnish/vefd.c

@@ -0,0 +1,163 @@
+/*-
+ * Copyright (c) 2025 Varnish Software AS
+ * All rights reserved.
+ *
+ * Author: Dridi Boukelmoune <[email protected]>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer
+ *    in this position and unchanged.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ */
+
+#include "config.h"
+
+#if HAVE_EVENTFD
+#  include <sys/eventfd.h>
+#else
+#  include <fcntl.h>
+#endif
+
+#include <errno.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <unistd.h>
+
+#include <vdef.h>
+#include <vefd.h>
+#include <vas.h>
+#include <miniobj.h>
+
+#if HAVE_EVENTFD
+int
+VEFD_Open(struct vefd *vefd)
+{
+
+	CHECK_OBJ_NOTNULL(vefd, VEFD_MAGIC);
+	assert(vefd->poll_fd == -1);
+	assert(vefd->priv_fd == -1);
+
+	vefd->poll_fd = eventfd(0, EFD_CLOEXEC | EFD_NONBLOCK);
+	return (vefd->poll_fd);
+}
+
+int
+VEFD_Signal(struct vefd *vefd)
+{
+	int64_t buf = 1;
+
+	CHECK_OBJ_NOTNULL(vefd, VEFD_MAGIC);
+	assert(vefd->poll_fd >= 0);
+	assert(vefd->priv_fd == -1);
+	assert(write(vefd->poll_fd, &buf, sizeof buf) == sizeof buf);
+	return (0);
+}
+
+int
+VEFD_Clear(struct vefd *vefd)
+{
+	int64_t buf;
+
+	CHECK_OBJ_NOTNULL(vefd, VEFD_MAGIC);
+	assert(vefd->poll_fd >= 0);
+	assert(vefd->priv_fd == -1);
+	assert(read(vefd->poll_fd, &buf, sizeof buf) == sizeof buf);
+	return (0);
+}
+
+int
+VEFD_Close(struct vefd *vefd)
+{
+
+	CHECK_OBJ_NOTNULL(vefd, VEFD_MAGIC);
+	assert(vefd->poll_fd >= 0);
+	assert(vefd->priv_fd == -1);
+	closefd(&vefd->poll_fd);
+	return (0);
+}
+#else /* !HAVE_EVENTFD */
+int
+VEFD_Open(struct vefd *vefd)
+{
+	int fd[2];
+
+	CHECK_OBJ_NOTNULL(vefd, VEFD_MAGIC);
+	assert(vefd->poll_fd == -1);
+	assert(vefd->priv_fd == -1);
+
+	if (pipe(fd) < 0)
+		return (-1);
+
+	AZ(fcntl(fd[0], F_SETFL, O_CLOEXEC|O_NONBLOCK));
+	AZ(fcntl(fd[1], F_SETFL, O_CLOEXEC|O_NONBLOCK));
+	vefd->poll_fd = fd[0];
+	vefd->priv_fd = fd[1];
+	return (0);
+}
+
+int
+VEFD_Signal(struct vefd *vefd)
+{
+	ssize_t r;
+
+	CHECK_OBJ_NOTNULL(vefd, VEFD_MAGIC);
+	assert(vefd->poll_fd >= 0);
+	assert(vefd->priv_fd >= 0);
+	assert(vefd->poll_fd != vefd->priv_fd);
+	r = write(vefd->priv_fd, "", 1);
+	if (r < 0 && errno != EAGAIN && errno != EWOULDBLOCK)
+		return (-1);
+	return (0);
+}
+
+int
+VEFD_Clear(struct vefd *vefd)
+{
+	char buf[64];
+	ssize_t r;
+
+	CHECK_OBJ_NOTNULL(vefd, VEFD_MAGIC);
+	assert(vefd->poll_fd >= 0);
+	assert(vefd->priv_fd >= 0);
+	assert(vefd->poll_fd != vefd->priv_fd);
+	do {
+		r = read(vefd->poll_fd, buf, sizeof buf);
+	} while (r > 0);
+	if (errno != EAGAIN && errno != EWOULDBLOCK)
+		return (-1);
+	return (0);
+}
+
+int
+VEFD_Close(struct vefd *vefd)
+{
+
+	CHECK_OBJ_NOTNULL(vefd, VEFD_MAGIC);
+	assert(vefd->poll_fd >= 0);
+	assert(vefd->priv_fd >= 0);
+	assert(vefd->poll_fd != vefd->priv_fd);
+	closefd(&vefd->poll_fd);
+	closefd(&vefd->priv_fd);
+	return (0);
+}
+#endif /* HAVE_EVENTFD */