sysfs: introduce sysfs module

Netconfig was the only user of sysfs but now other modules will
also need it.

Adding existing API for IPv6 settings, a IPv4 and IPv6 'supports'
checker, and a setter for IPv4 settings.

Makefile.am

@@ -246,6 +246,7 @@ src_iwd_SOURCES = src/main.c linux/nl80211.h src/iwd.h src/missing.h \
 					src/diagnostic.h src/diagnostic.c \
 					src/ip-pool.h src/ip-pool.c \
 					src/band.h src/band.c \
+					src/sysfs.h src/sysfs.c \
 					$(eap_sources) \
 					$(builtin_sources)
 

src/sysfs.c

@@ -0,0 +1,109 @@
+/*
+ *
+ *  Wireless daemon for Linux
+ *
+ *  Copyright (C) 2021  Intel Corporation. All rights reserved.
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, write to the Free Software
+ *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <sys/stat.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <ell/ell.h>
+
+#include "src/sysfs.h"
+
+static int write_string(const char *file, const char *value)
+{
+	size_t l = strlen(value);
+	int fd;
+	int r;
+
+	fd = L_TFR(open(file, O_WRONLY));
+	if (fd < 0)
+		return -errno;
+
+	r = L_TFR(write(fd, value, l));
+	L_TFR(close(fd));
+
+	return r;
+}
+
+static bool sysfs_supports_ip_setting(const char *ipv, const char *ifname,
+					const char *setting)
+{
+	struct stat st;
+	int err;
+	L_AUTO_FREE_VAR(char *, file) =
+		l_strdup_printf("/proc/sys/net/%s/conf/%s/%s", ipv,
+							ifname, setting);
+
+	err = stat(file, &st);
+
+	if (!err && S_ISREG(st.st_mode) != 0)
+		return true;
+
+	return false;
+}
+
+bool sysfs_supports_ipv6_setting(const char *ifname, const char *setting)
+{
+	return sysfs_supports_ip_setting("ipv6", ifname, setting);
+}
+
+int sysfs_write_ipv6_setting(const char *ifname, const char *setting,
+					const char *value)
+{
+	int r;
+
+	L_AUTO_FREE_VAR(char *, file) =
+		l_strdup_printf("/proc/sys/net/ipv6/conf/%s/%s",
+							ifname, setting);
+
+	r = write_string(file, value);
+	if (r < 0)
+		l_error("Unable to write %s to %s", setting, file);
+
+	return r;
+}
+
+bool sysfs_supports_ipv4_setting(const char *ifname, const char *setting)
+{
+	return sysfs_supports_ip_setting("ipv4", ifname, setting);
+}
+
+int sysfs_write_ipv4_setting(const char *ifname, const char *setting,
+					const char *value)
+{
+	int r;
+
+	L_AUTO_FREE_VAR(char *, file) =
+		l_strdup_printf("/proc/sys/net/ipv4/conf/%s/%s",
+							ifname, setting);
+
+	r = write_string(file, value);
+	if (r < 0)
+		l_error("Unable to write %s to %s", setting, file);
+
+	return r;
+}

src/sysfs.h

@@ -0,0 +1,28 @@
+/*
+ *
+ *  Wireless daemon for Linux
+ *
+ *  Copyright (C) 2021  Intel Corporation. All rights reserved.
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, write to the Free Software
+ *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ */
+
+bool sysfs_supports_ipv6_setting(const char *ifname, const char *setting);
+int sysfs_write_ipv6_setting(const char *ifname, const char *setting,
+					const char *value);
+bool sysfs_supports_ipv4_setting(const char *ifname, const char *setting);
+int sysfs_write_ipv4_setting(const char *ifname, const char *setting,
+					const char *value);