libutil: rename runProgram redirections to make more sense

the `from`/`to` naming only made sense for unidirectional output fds,
for others (and for the dup2 api in general) it was backwards. rename
them to `dup`/`from` to make this look more like the assignment it is

Change-Id: Iee50d06f9cfcea765ace6cfbe85b192829207e5f

lix/libfetchers/git.cc

@@ -177,7 +177,7 @@ WorkdirInfo getWorkdirInfo(const Input & input, const Path & workdir)
              "--no-revs",
              "HEAD^{commit}"},
         .environment = env,
-        .redirections = {{.from = STDERR_FILENO, .to = STDOUT_FILENO}},
+        .redirections = {{.dup = STDERR_FILENO, .from = STDOUT_FILENO}},
     });
     auto exitCode = WEXITSTATUS(result.first);
     auto errorMessage = result.second;
@@ -723,7 +723,7 @@ struct GitInputScheme : InputScheme
             .args =
                 {"-C", repoDir, "--git-dir", gitDir, "cat-file", "commit", input.getRev()->gitRev()
                 },
-            .redirections = {{.from = STDERR_FILENO, .to = STDOUT_FILENO}},
+            .redirections = {{.dup = STDERR_FILENO, .from = STDOUT_FILENO}},
         });
         if (WEXITSTATUS(result.first) == 128
             && result.second.find("bad file") != std::string::npos)

lix/libstore/build/derivation-goal.cc

@@ -892,7 +892,7 @@ void runPostBuildHook(
         .program = settings.postBuildHook,
         .environment = hookEnvironment,
         .captureStdout = true,
-        .redirections = {{.from = STDERR_FILENO, .to = STDOUT_FILENO}},
+        .redirections = {{.dup = STDERR_FILENO, .from = STDOUT_FILENO}},
     });
     Finally const _wait([&] {
         try {

lix/libstore/globals.cc

@@ -249,7 +249,7 @@ StringSet Settings::getDefaultExtraPlatforms()
         && runProgram(RunOptions{
                           .program = "arch",
                           .args = {"-arch", "x86_64", "/usr/bin/true"},
-                          .redirections = {{.from = STDERR_FILENO, .to = STDOUT_FILENO}}
+                          .redirections = {{.dup = STDERR_FILENO, .from = STDOUT_FILENO}}
                       }
            ).first
             == 0)

lix/libstore/platform/linux.cc

@@ -1100,13 +1100,13 @@ Pid LinuxLocalDerivationGoal::startChild(std::function<void()> openSlave)
             // descriptors very early and lacks fd arguments for the namespaces we
             // want it to join. we cannot have pasta join the namespaces via pids;
             // doing so requires capabilities which pasta *also* drops very early.
-            .redirections = {
-                {.from = 0, .to = netns.get()},
-                {.from = 1, .to = userns ? userns.get() : 1},
-            },
-            .caps = getuid() == 0
-                ? std::set<long>{CAP_SYS_ADMIN, CAP_NET_BIND_SERVICE}
-                : std::set<long>{},
+            .redirections =
+                {
+                    {.dup = 0, .from = netns.get()},
+                    {.dup = 1, .from = userns ? userns.get() : 1},
+                },
+            .caps = getuid() == 0 ? std::set<long>{CAP_SYS_ADMIN, CAP_NET_BIND_SERVICE}
+                                  : std::set<long>{},
         });
     }
 

lix/libutil/processes.cc

@@ -332,8 +332,8 @@ RunningProgram runProgram2(const RunOptions & options)
         if (options.captureStdout && dup2(out.writeSide.get(), STDOUT_FILENO) == -1)
             throw SysError("dupping stdout");
         for (auto redirection : options.redirections) {
-            if (dup2(redirection.to, redirection.from) == -1) {
-                throw SysError("dupping fd %i to %i", redirection.from, redirection.to);
+            if (dup2(redirection.from, redirection.dup) == -1) {
+                throw SysError("dupping fd %i to %i", redirection.dup, redirection.from);
             }
         }
 

lix/libutil/processes.hh

@@ -78,7 +78,7 @@ struct RunOptions
 {
     struct Redirection
     {
-        int from, to;
+        int dup, from;
     };
 
     Path program;