Detect lsof

Also, don't use lsof on Linux since it's not needed.

Fixes #1328.

Makefile.config.in

@@ -15,6 +15,7 @@ SQLITE3_LIBS = @SQLITE3_LIBS@
 bash = @bash@
 bindir = @bindir@
 bro = @bro@
+lsof = @lsof@
 datadir = @datadir@
 datarootdir = @datarootdir@
 docdir = @docdir@

configure.ac

@@ -128,6 +128,7 @@ NEED_PROG(xz, xz)
 AC_PATH_PROG(dot, dot)
 AC_PATH_PROG(pv, pv, pv)
 AC_PATH_PROG(bro, bro, bro)
+AC_PATH_PROG(lsof, lsof, lsof)
 
 
 NEED_PROG(cat, cat)

src/libstore/gc.cc

@@ -426,22 +426,27 @@ void LocalStore::findRuntimeRoots(PathSet & roots)
             throw SysError("iterating /proc");
     }
 
+#if !defined(__linux__)
     try {
-        auto lsofRegex = std::regex(R"(^n(/.*)$)");
+        printError("RUN LSOF %s", LSOF);
+        std::regex lsofRegex(R"(^n(/.*)$)");
         auto lsofLines =
-            tokenizeString<std::vector<string>>(runProgram("lsof", true, { "-n", "-w", "-F", "n" }), "\n");
+            tokenizeString<std::vector<string>>(runProgram(LSOF, true, { "-n", "-w", "-F", "n" }), "\n");
         for (const auto & line : lsofLines) {
-            auto match = std::smatch{};
+            std::smatch match;
             if (std::regex_match(line, match, lsofRegex))
                 paths.emplace(match[1]);
         }
     } catch (ExecError & e) {
         /* lsof not installed, lsof failed */
     }
+#endif
 
+#if defined(__linux__)
     readFileRoots("/proc/sys/kernel/modprobe", paths);
     readFileRoots("/proc/sys/kernel/fbsplash", paths);
     readFileRoots("/proc/sys/kernel/poweroff_cmd", paths);
+#endif
 
     for (auto & i : paths)
         if (isInStore(i)) {

src/libstore/local.mk

@@ -27,7 +27,8 @@ libstore_CXXFLAGS = \
  -DNIX_CONF_DIR=\"$(sysconfdir)/nix\" \
  -DNIX_LIBEXEC_DIR=\"$(libexecdir)\" \
  -DNIX_BIN_DIR=\"$(bindir)\" \
- -DBASH_PATH="\"$(bash)\""
+ -DBASH_PATH="\"$(bash)\"" \
+ -DLSOF=\"$(lsof)\"
 
 $(d)/local-store.cc: $(d)/schema.sql.hh