add libsync.h helper

Rather than cut/pasting these couple ioctl wrappers everywhere, just
stuff them as static-inline into a header.

This is probably mostly used from mesa, but some drivers, test apps, etc
may also want to use it from libdrm.

v2: handle EINTR, add sync_accumulate() based on #dri-devel discussion,
    etc

Signed-off-by: Rob Clark <robclark@freedesktop.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

Makefile.sources

@@ -13,6 +13,7 @@ LIBDRM_FILES := \
 	util_math.h
 
 LIBDRM_H_FILES := \
+	libsync.h \
 	xf86drm.h \
 	xf86drmMode.h
 

libsync.h

@@ -0,0 +1,148 @@
+/*
+ *  sync abstraction
+ *  Copyright 2015-2016 Collabora Ltd.
+ *
+ *  Based on the implementation from the Android Open Source Project,
+ *
+ *  Copyright 2012 Google, Inc
+ *
+ *  Permission is hereby granted, free of charge, to any person obtaining a
+ *  copy of this software and associated documentation files (the "Software"),
+ *  to deal in the Software without restriction, including without limitation
+ *  the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ *  and/or sell copies of the Software, and to permit persons to whom the
+ *  Software is furnished to do so, subject to the following conditions:
+ *
+ *  The above copyright notice and this permission notice shall be included in
+ *  all copies or substantial portions of the Software.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ *  THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ *  OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ *  ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ *  OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef _LIBSYNC_H
+#define _LIBSYNC_H
+
+#include <assert.h>
+#include <errno.h>
+#include <stdint.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/poll.h>
+#include <unistd.h>
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+#ifndef SYNC_IOC_MERGE
+/* duplicated from linux/sync_file.h to avoid build-time dependency
+ * on new (v4.7) kernel headers.  Once distro's are mostly using
+ * something newer than v4.7 drop this and #include <linux/sync_file.h>
+ * instead.
+ */
+struct sync_merge_data {
+	char	name[32];
+	int32_t	fd2;
+	int32_t	fence;
+	uint32_t	flags;
+	uint32_t	pad;
+};
+#define SYNC_IOC_MAGIC		'>'
+#define SYNC_IOC_MERGE		_IOWR(SYNC_IOC_MAGIC, 3, struct sync_merge_data)
+#endif
+
+
+static inline int sync_wait(int fd, int timeout)
+{
+	struct pollfd fds = {0};
+	int ret;
+
+	fds.fd = fd;
+	fds.events = POLLIN;
+
+	do {
+		ret = poll(&fds, 1, timeout);
+		if (ret > 0) {
+			if (fds.revents & (POLLERR | POLLNVAL)) {
+				errno = EINVAL;
+				return -1;
+			}
+			return 0;
+		} else if (ret == 0) {
+			errno = ETIME;
+			return -1;
+		}
+	} while (ret == -1 && (errno == EINTR || errno == EAGAIN));
+
+	return ret;
+}
+
+static inline int sync_merge(const char *name, int fd1, int fd2)
+{
+	struct sync_merge_data data = {0};
+	int ret;
+
+	data.fd2 = fd2;
+	strncpy(data.name, name, sizeof(data.name));
+
+	do {
+		ret = ioctl(fd1, SYNC_IOC_MERGE, &data);
+	} while (ret == -1 && (errno == EINTR || errno == EAGAIN));
+
+	if (ret < 0)
+		return ret;
+
+	return data.fence;
+}
+
+/* accumulate fd2 into fd1.  If *fd1 is not a valid fd then dup fd2,
+ * otherwise sync_merge() and close the old *fd1.  This can be used
+ * to implement the pattern:
+ *
+ *    init()
+ *    {
+ *       batch.fence_fd = -1;
+ *    }
+ *
+ *    // does *NOT* take ownership of fd
+ *    server_sync(int fd)
+ *    {
+ *       if (sync_accumulate("foo", &batch.fence_fd, fd)) {
+ *          ... error ...
+ *       }
+ *    }
+ */
+static inline int sync_accumulate(const char *name, int *fd1, int fd2)
+{
+	int ret;
+
+	assert(fd2 >= 0);
+
+	if (*fd1 < 0) {
+		*fd1 = dup(fd2);
+		return 0;
+	}
+
+	ret = sync_merge(name, *fd1, fd2);
+	if (ret < 0) {
+		/* leave *fd1 as it is */
+		return ret;
+	}
+
+	close(*fd1);
+	*fd1 = ret;
+
+	return 0;
+}
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif