diff --git a/cmdline.cc b/cmdline.cc
index b24a549..17ed5d7 100644
--- a/cmdline.cc
+++ b/cmdline.cc
@@ -242,7 +242,7 @@ void logParams(nsjconf_t* nsjconf) {
 	    logYesNo(nsjconf->disable_no_new_privs), nsjconf->max_cpus);
 
 	for (const auto& p : nsjconf->mountpts) {
-		LOG_I("%s: %s", p.isSymlink ? "Symlink" : "Mount point",
+		LOG_I("%s: %s", p.is_symlink ? "Symlink" : "Mount point",
 		    mnt::describeMountPt(p).c_str());
 	}
 	for (const auto& uid : nsjconf->uids) {
@@ -603,11 +603,11 @@ std::unique_ptr<nsjconf_t> parseArgs(int argc, char* argv[]) {
 			if (dst.empty()) {
 				dst = src;
 			}
-			if (!mnt::addMountPtTail(nsjconf.get(), src.c_str(), dst.c_str(),
-				/* fs_type= */ "", /* options= */ "",
-				MS_BIND | MS_REC | MS_PRIVATE | MS_RDONLY,
-				/* isDir= */ mnt::NS_DIR_MAYBE, /* mandatory= */ true, NULL, NULL,
-				NULL, 0, /* is_symlink= */ false)) {
+			if (!mnt::addMountPtTail(nsjconf.get(), src, dst, /* fs_type= */ "",
+				/* options= */ "", MS_BIND | MS_REC | MS_PRIVATE | MS_RDONLY,
+				/* is_dir= */ mnt::NS_DIR_MAYBE, /* is_mandatory= */ true,
+				/* src_env= */ "", /* dst_env= */ "", /* src_content= */ "",
+				/* is_symlink= */ false)) {
 				return nullptr;
 			}
 		}; break;
@@ -617,18 +617,19 @@ std::unique_ptr<nsjconf_t> parseArgs(int argc, char* argv[]) {
 			if (dst.empty()) {
 				dst = src;
 			}
-			if (!mnt::addMountPtTail(nsjconf.get(), src.c_str(), dst.c_str(),
-				/* fs_type= */ "", /* options= */ "", MS_BIND | MS_REC | MS_PRIVATE,
-				/* isDir= */ mnt::NS_DIR_MAYBE, /* mandatory= */ true, NULL, NULL,
-				NULL, 0, /* is_symlink= */ false)) {
+			if (!mnt::addMountPtTail(nsjconf.get(), src, dst, /* fs_type= */ "",
+				/* options= */ "", MS_BIND | MS_REC | MS_PRIVATE,
+				/* is_dir= */ mnt::NS_DIR_MAYBE, /* is_mandatory= */ true,
+				/* src_env= */ "", /* dst_env= */ "", /* src_content= */ "",
+				/* is_symlink= */ false)) {
 				return nullptr;
 			}
 		}; break;
 		case 'T': {
-			if (!mnt::addMountPtTail(nsjconf.get(), /* src= */ NULL, optarg, "tmpfs",
+			if (!mnt::addMountPtTail(nsjconf.get(), /* src= */ "", optarg, "tmpfs",
 				/* options= */ cmdlineTmpfsSz, /* flags= */ 0,
-				/* isDir= */ mnt::NS_DIR_YES,
-				/* mandatory= */ true, NULL, NULL, NULL, 0,
+				/* is_dir= */ mnt::NS_DIR_YES, /* is_mandatory= */ true,
+				/* src_env= */ "", /* dst_env= */ "", /* src_content= */ "",
 				/* is_symlink= */ false)) {
 				return nullptr;
 			}
@@ -641,11 +642,11 @@ std::unique_ptr<nsjconf_t> parseArgs(int argc, char* argv[]) {
 			}
 			std::string fs_type = argByColon(optarg, 2);
 			std::string options = argByColon(optarg, 3);
-			if (!mnt::addMountPtTail(nsjconf.get(), src.c_str(), dst.c_str(),
-				/* fs_type= */ fs_type.c_str(), /* options= */ options.c_str(),
-				/* flags= */ 0,
-				/* isDir= */ mnt::NS_DIR_MAYBE, /* mandatory= */ true, NULL, NULL,
-				NULL, 0, /* is_symlink= */ false)) {
+			if (!mnt::addMountPtTail(nsjconf.get(), src, dst, /* fs_type= */ fs_type,
+				/* options= */ options, /* flags= */ 0,
+				/* is_dir= */ mnt::NS_DIR_MAYBE, /* is_mandatory= */ true,
+				/* src_env= */ "", /* dst_env= */ "", /* src_content= */ "",
+				/* is_symlink= */ false)) {
 				return nullptr;
 			}
 		}; break;
@@ -745,28 +746,28 @@ std::unique_ptr<nsjconf_t> parseArgs(int argc, char* argv[]) {
 	}
 
 	if (!nsjconf->proc_path.empty()) {
-		if (!mnt::addMountPtTail(nsjconf.get(), /* src= */ NULL, nsjconf->proc_path.c_str(),
-			"proc", "", nsjconf->is_proc_rw ? 0 : MS_RDONLY,
-			/* isDir= */ mnt::NS_DIR_YES,
-			/* mandatory= */ true, NULL, NULL, NULL, 0, /* is_symlink= */ false)) {
+		if (!mnt::addMountPtTail(nsjconf.get(), /* src= */ "", nsjconf->proc_path, "proc",
+			/* options= */ "", nsjconf->is_proc_rw ? 0 : MS_RDONLY,
+			/* is_dir= */ mnt::NS_DIR_YES, /* is_mandatory= */ true, /* src_env= */ "",
+			/* dst_env= */ "", /* src_content= */ "", /* is_symlink= */ false)) {
 			return nullptr;
 		}
 	}
 	if (!(nsjconf->chroot.empty())) {
-		if (!mnt::addMountPtHead(nsjconf.get(), nsjconf->chroot.c_str(), "/",
-			/* fs_type= */ "",
+		if (!mnt::addMountPtHead(nsjconf.get(), nsjconf->chroot, "/", /* fs_type= */ "",
 			/* options= */ "",
 			nsjconf->is_root_rw ? (MS_BIND | MS_REC | MS_PRIVATE)
 					    : (MS_BIND | MS_REC | MS_PRIVATE | MS_RDONLY),
-			/* isDir= */ mnt::NS_DIR_YES, /* mandatory= */ true, NULL, NULL, NULL, 0,
-			/* is_symlink= */ false)) {
+			/* is_dir= */ mnt::NS_DIR_YES, /* is_mandatory= */ true, /* src_env= */ "",
+			/* dst_env= */ "", /* src_content= */ "", /* is_symlink= */ false)) {
 			return nullptr;
 		}
 	} else {
-		if (!mnt::addMountPtHead(nsjconf.get(), /* src= */ NULL, "/", "tmpfs",
+		if (!mnt::addMountPtHead(nsjconf.get(), /* src= */ "", "/", "tmpfs",
 			/* options= */ "", nsjconf->is_root_rw ? 0 : MS_RDONLY,
-			/* isDir= */ mnt::NS_DIR_YES,
-			/* mandatory= */ true, NULL, NULL, NULL, 0, /* is_symlink= */ false)) {
+			/* is_dir= */ mnt::NS_DIR_YES,
+			/* is_mandatory= */ true, /* src_env= */ "", /* dst_env= */ "",
+			/* src_content= */ "", /* is_symlink= */ false)) {
 			return nullptr;
 		}
 	}
diff --git a/config.cc b/config.cc
index 5abb1b0..d60686f 100644
--- a/config.cc
+++ b/config.cc
@@ -200,39 +200,28 @@ static bool configParseInternal(nsjconf_t* nsjconf, const nsjail::NsJailConfig&
 		nsjconf->proc_path.clear();
 	}
 	for (ssize_t i = 0; i < njc.mount_size(); i++) {
-		const char* src = (njc.mount(i).has_src()) ? njc.mount(i).src().c_str() : NULL;
-		const char* src_env = (njc.mount(i).has_prefix_src_env())
-					  ? njc.mount(i).prefix_src_env().c_str()
-					  : NULL;
-		const char* dst = (njc.mount(i).has_dst()) ? njc.mount(i).dst().c_str() : NULL;
-		const char* dst_env = (njc.mount(i).has_prefix_dst_env())
-					  ? njc.mount(i).prefix_dst_env().c_str()
-					  : NULL;
-		const char* fstype =
-		    (njc.mount(i).has_fstype()) ? njc.mount(i).fstype().c_str() : NULL;
-		const char* options =
-		    (njc.mount(i).has_options()) ? njc.mount(i).options().c_str() : NULL;
+		std::string src = njc.mount(i).src();
+		std::string src_env = njc.mount(i).prefix_src_env();
+		std::string dst = njc.mount(i).dst();
+		std::string dst_env = njc.mount(i).prefix_dst_env();
+		std::string fstype = njc.mount(i).fstype();
+		std::string options = njc.mount(i).options();
 
 		uintptr_t flags = (njc.mount(i).rw() == false) ? MS_RDONLY : 0;
 		flags |= njc.mount(i).is_bind() ? (MS_BIND | MS_REC | MS_PRIVATE) : 0;
-		bool mandatory = njc.mount(i).mandatory();
+		bool is_mandatory = njc.mount(i).mandatory();
+		bool is_symlink = njc.mount(i).is_symlink();
+		std::string src_content = njc.mount(i).src_content();
 
-		mnt::isDir_t isDir = mnt::NS_DIR_MAYBE;
+		mnt::isDir_t is_dir = mnt::NS_DIR_MAYBE;
 		if (njc.mount(i).has_is_dir()) {
-			isDir = njc.mount(i).is_dir() ? mnt::NS_DIR_YES : mnt::NS_DIR_NO;
+			is_dir = njc.mount(i).is_dir() ? mnt::NS_DIR_YES : mnt::NS_DIR_NO;
 		}
 
-		const char* src_content = NULL;
-		size_t src_content_len = 0;
-		if (njc.mount(i).has_src_content()) {
-			src_content = njc.mount(i).src_content().data();
-			src_content_len = njc.mount(i).src_content().size();
-		}
-
-		if (mnt::addMountPtTail(nsjconf, src, dst, fstype, options, flags, isDir, mandatory,
-			src_env, dst_env, src_content, src_content_len,
-			njc.mount(i).is_symlink()) == false) {
-			LOG_E("Couldn't add mountpoint for src:'%s' dst:'%s'", src, dst);
+		if (!mnt::addMountPtTail(nsjconf, src, dst, fstype, options, flags, is_dir,
+			is_mandatory, src_env, dst_env, src_content, is_symlink)) {
+			LOG_E("Couldn't add mountpoint for src:'%s' dst:'%s'", src.c_str(),
+			    dst.c_str());
 			return false;
 		}
 	}
diff --git a/config.proto b/config.proto
index 4a97674..eb5f709 100644
--- a/config.proto
+++ b/config.proto
@@ -27,15 +27,15 @@ message IdMap {
 }
 message MountPt {
     /* Can be skipped for filesystems like 'proc' */
-    optional string src = 1;
+    optional string src = 1 [default = ""];
     /* Should 'src' path be prefixed with this envvar? */
-    optional string prefix_src_env = 2;
+    optional string prefix_src_env = 2 [default = ""];
     /* If specified, contains buffer that will be written to the dst file */
-    optional bytes src_content = 3;
+    optional bytes src_content = 3 [default = ""];
     /* Mount point inside jail */
-    required string dst = 4;
+    required string dst = 4 [default = ""];
     /* Should 'dst' path be prefixed with this envvar? */
-    optional string prefix_dst_env = 5;
+    optional string prefix_dst_env = 5 [default = ""];
     /* Can be empty for mount --bind mounts */
     optional string fstype = 6 [default = ""];
     /* E.g. size=5000000 for 'tmpfs' */
diff --git a/mnt.cc b/mnt.cc
index 9f175ad..d6ec47c 100644
--- a/mnt.cc
+++ b/mnt.cc
@@ -133,12 +133,12 @@ static bool mountPt(mount_t* mpt, const char* newroot, const char* tmpdir) {
 		snprintf(srcpath, sizeof(srcpath), "none");
 	}
 
-	if (mpt->isSymlink) {
+	if (mpt->is_symlink) {
 		if (!util::createDirRecursively(dst)) {
 			LOG_W("Couldn't create upper directories for '%s'", dst);
 			return false;
 		}
-	} else if (mpt->isDir) {
+	} else if (mpt->is_dir) {
 		if (!util::createDirRecursively(dst)) {
 			LOG_W("Couldn't create upper directories for '%s'", dst);
 			return false;
@@ -159,10 +159,10 @@ static bool mountPt(mount_t* mpt, const char* newroot, const char* tmpdir) {
 		}
 	}
 
-	if (mpt->isSymlink) {
+	if (mpt->is_symlink) {
 		LOG_D("symlink('%s', '%s')", srcpath, dst);
 		if (symlink(srcpath, dst) == -1) {
-			if (mpt->mandatory) {
+			if (mpt->is_mandatory) {
 				PLOG_W("symlink('%s', '%s')", srcpath, dst);
 				return false;
 			} else {
@@ -230,7 +230,7 @@ static bool remountRO(const mount_t& mpt) {
 	if (!mpt.mounted) {
 		return true;
 	}
-	if (mpt.isSymlink) {
+	if (mpt.is_symlink) {
 		return true;
 	}
 	if ((mpt.flags & MS_RDONLY) == 0) {
@@ -371,7 +371,7 @@ static bool initNsInternal(nsjconf_t* nsjconf) {
 	}
 
 	for (auto& p : nsjconf->mountpts) {
-		if (!mountPt(&p, destdir, tmpdir) && p.mandatory) {
+		if (!mountPt(&p, destdir, tmpdir) && p.is_mandatory) {
 			return false;
 		}
 	}
@@ -402,7 +402,7 @@ static bool initNsInternal(nsjconf_t* nsjconf) {
 	}
 
 	for (const auto& p : nsjconf->mountpts) {
-		if (!remountRO(p) && p.mandatory) {
+		if (!remountRO(p) && p.is_mandatory) {
 			return false;
 		}
 	}
@@ -437,92 +437,84 @@ bool initNs(nsjconf_t* nsjconf) {
 	return false;
 }
 
-static bool addMountPt(mount_t* mnt, const char* src, const char* dst, const char* fstype,
-    const char* options, uintptr_t flags, isDir_t isDir, bool mandatory, const char* src_env,
-    const char* dst_env, const char* src_content, size_t src_content_len, bool is_symlink) {
-	if (src_env) {
-		const char* e = getenv(src_env);
+static bool addMountPt(mount_t* mnt, const std::string& src, const std::string& dst,
+    const std::string& fstype, const std::string& options, uintptr_t flags, isDir_t is_dir,
+    bool is_mandatory, const std::string& src_env, const std::string& dst_env,
+    const std::string& src_content, bool is_symlink) {
+	if (!src_env.empty()) {
+		const char* e = getenv(src_env.c_str());
 		if (e == NULL) {
-			LOG_W("No such envvar:'%s'", src_env);
+			LOG_W("No such envvar:'%s'", src_env.c_str());
 			return false;
 		}
 		mnt->src = e;
 	}
-	if (src) {
-		mnt->src.append(src);
-	}
+	mnt->src.append(src);
 
-	if (dst_env) {
-		const char* e = getenv(dst_env);
+	if (!dst_env.empty()) {
+		const char* e = getenv(dst_env.c_str());
 		if (e == NULL) {
-			LOG_W("No such envvar:'%s'", dst_env);
+			LOG_W("No such envvar:'%s'", dst_env.c_str());
 			return false;
 		}
 		mnt->dst = e;
 	}
-	if (dst) {
-		mnt->dst.append(dst);
-	}
+	mnt->dst.append(dst);
 
-	if (fstype) {
-		mnt->fs_type = fstype;
-	}
-	if (options) {
-		mnt->options = options;
-	}
-	if (src_content) {
-		mnt->src_content.assign(src_content, src_content_len);
-	}
+	mnt->fs_type = fstype;
+	mnt->options = options;
 	mnt->flags = flags;
-	mnt->isDir = true;
-	mnt->isSymlink = is_symlink;
-	mnt->mandatory = mandatory;
+	mnt->is_symlink = is_symlink;
+	mnt->is_mandatory = is_mandatory;
 	mnt->mounted = false;
+	mnt->src_content = src_content;
 
-	switch (isDir) {
+	switch (is_dir) {
 	case NS_DIR_YES:
-		mnt->isDir = true;
+		mnt->is_dir = true;
 		break;
 	case NS_DIR_NO:
-		mnt->isDir = false;
+		mnt->is_dir = false;
 		break;
 	case NS_DIR_MAYBE: {
-		if (src_content) {
-			mnt->isDir = false;
+		if (!src_content.empty()) {
+			mnt->is_dir = false;
 		} else if (mnt->src.empty()) {
-			mnt->isDir = true;
+			mnt->is_dir = true;
 		} else if (mnt->flags & MS_BIND) {
-			mnt->isDir = mnt::isDir(mnt->src.c_str());
+			mnt->is_dir = mnt::isDir(mnt->src.c_str());
 		} else {
-			mnt->isDir = true;
+			mnt->is_dir = true;
 		}
 	} break;
 	default:
-		LOG_F("Unknown isDir value: %d", isDir);
-		break;
+		LOG_E("Unknown is_dir value: %d", is_dir);
+		return false;
 	}
 
 	return true;
 }
 
-bool addMountPtHead(nsjconf_t* nsjconf, const char* src, const char* dst, const char* fstype,
-    const char* options, uintptr_t flags, isDir_t isDir, bool mandatory, const char* src_env,
-    const char* dst_env, const char* src_content, size_t src_content_len, bool is_symlink) {
+bool addMountPtHead(nsjconf_t* nsjconf, const std::string& src, const std::string& dst,
+    const std::string& fstype, const std::string& options, uintptr_t flags, isDir_t is_dir,
+    bool is_mandatory, const std::string& src_env, const std::string& dst_env,
+    const std::string& src_content, bool is_symlink) {
 	mount_t mnt;
-	if (!addMountPt(&mnt, src, dst, fstype, options, flags, isDir, mandatory, src_env, dst_env,
-		src_content, src_content_len, is_symlink)) {
+	if (!addMountPt(&mnt, src, dst, fstype, options, flags, is_dir, is_mandatory, src_env,
+		dst_env, src_content, is_symlink)) {
 		return false;
 	}
 	nsjconf->mountpts.insert(nsjconf->mountpts.begin(), mnt);
 	return true;
 }
 
-bool addMountPtTail(nsjconf_t* nsjconf, const char* src, const char* dst, const char* fstype,
-    const char* options, uintptr_t flags, isDir_t isDir, bool mandatory, const char* src_env,
-    const char* dst_env, const char* src_content, size_t src_content_len, bool is_symlink) {
+bool addMountPtTail(nsjconf_t* nsjconf, const std::string& src, const std::string& dst,
+    const std::string& fstype, const std::string& options, uintptr_t flags, isDir_t is_dir,
+    bool is_mandatory, const std::string& src_env, const std::string& dst_env,
+    const std::string& src_content, bool is_symlink) {
 	mount_t mnt;
-	if (!addMountPt(&mnt, src, dst, fstype, options, flags, isDir, mandatory, src_env, dst_env,
-		src_content, src_content_len, is_symlink)) {
+	if (!addMountPt(&mnt, src, dst, fstype, options, flags, is_dir, is_mandatory, src_env,
+		dst_env, src_content, is_symlink)) {
 		return false;
 	}
 	nsjconf->mountpts.push_back(mnt);
@@ -535,16 +527,16 @@ const std::string describeMountPt(const mount_t& mpt) {
 	snprintf(mount_pt_descr, sizeof(mount_pt_descr),
 	    "src:'%s' dst:'%s' type:'%s' flags:%s options:'%s' isDir:%s", mpt.src.c_str(),
 	    mpt.dst.c_str(), mpt.fs_type.c_str(), flagsToStr(mpt.flags).c_str(),
-	    mpt.options.c_str(), mpt.isDir ? "true" : "false");
+	    mpt.options.c_str(), mpt.is_dir ? "true" : "false");
 
-	if (!mpt.mandatory) {
+	if (!mpt.is_mandatory) {
 		util::sSnPrintf(mount_pt_descr, sizeof(mount_pt_descr), " mandatory:false");
 	}
 	if (!mpt.src_content.empty()) {
 		util::sSnPrintf(mount_pt_descr, sizeof(mount_pt_descr), " src_content_len:%zu",
 		    mpt.src_content.length());
 	}
-	if (mpt.isSymlink) {
+	if (mpt.is_symlink) {
 		util::sSnPrintf(mount_pt_descr, sizeof(mount_pt_descr), " symlink:true");
 	}
 
diff --git a/mnt.h b/mnt.h
index 4237853..9b177f9 100644
--- a/mnt.h
+++ b/mnt.h
@@ -38,12 +38,14 @@ typedef enum {
 } isDir_t;
 
 bool initNs(nsjconf_t* nsjconf);
-bool addMountPtHead(nsjconf_t* nsjconf, const char* src, const char* dst, const char* fstype,
-    const char* options, uintptr_t flags, isDir_t isDir, bool mandatory, const char* src_env,
-    const char* dst_env, const char* src_content, size_t src_content_len, bool is_symlink);
-bool addMountPtTail(nsjconf_t* nsjconf, const char* src, const char* dst, const char* fstype,
-    const char* options, uintptr_t flags, isDir_t isDir, bool mandatory, const char* src_env,
-    const char* dst_env, const char* src_content, size_t src_content_len, bool is_symlink);
+bool addMountPtHead(nsjconf_t* nsjconf, const std::string& src, const std::string& dst,
+    const std::string& fstype, const std::string& options, uintptr_t flags, isDir_t is_dir,
+    bool is_mandatory, const std::string& src_env, const std::string& dst_env,
+    const std::string& src_content, bool is_symlink);
+bool addMountPtTail(nsjconf_t* nsjconf, const std::string& src, const std::string& dst,
+    const std::string& fstype, const std::string& options, uintptr_t flags, isDir_t is_dir,
+    bool is_mandatory, const std::string& src_env, const std::string& dst_env,
+    const std::string& src_content, bool is_symlink);
 const std::string describeMountPt(const mount_t& mpt);
 
 }  // namespace mnt
diff --git a/nsjail.h b/nsjail.h
index b7bd1e6..238f5c2 100644
--- a/nsjail.h
+++ b/nsjail.h
@@ -61,9 +61,9 @@ struct mount_t {
 	std::string fs_type;
 	std::string options;
 	uintptr_t flags;
-	bool isDir;
-	bool isSymlink;
-	bool mandatory;
+	bool is_dir;
+	bool is_symlink;
+	bool is_mandatory;
 	bool mounted;
 };