Merge remote-tracking branch 'origin/master' into flakes

16 files changed, 370 insertions, 158 deletions

diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index abf3669b5..279ae62f6 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -38,6 +38,12 @@ static AutoCloseFD openSlotLock(const Machine & m, unsigned long long slot)
     return openLockFile(fmt("%s/%s-%d", currentLoad, escapeUri(m.storeUri), slot), true);
 }
 
+static bool allSupportedLocally(const std::set<std::string>& requiredFeatures) {
+    for (auto & feature : requiredFeatures)
+        if (!settings.systemFeatures.get().count(feature)) return false;
+    return true;
+}
+
 static int _main(int argc, char * * argv)
 {
     {
@@ -97,9 +103,10 @@ static int _main(int argc, char * * argv)
             source >> drvPath;
             auto requiredFeatures = readStrings<std::set<std::string>>(source);
 
-            auto canBuildLocally = amWilling
-                &&  (  neededSystem == settings.thisSystem
-                    || settings.extraPlatforms.get().count(neededSystem) > 0);
+             auto canBuildLocally = amWilling
+                 &&  (  neededSystem == settings.thisSystem
+                     || settings.extraPlatforms.get().count(neededSystem) > 0)
+                 &&  allSupportedLocally(requiredFeatures);
 
             /* Error ignored here, will be caught later */
             mkdir(currentLoad.c_str(), 0777);
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 548eef31b..4bd1280ad 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -131,6 +131,16 @@ std::ostream & operator << (std::ostream & str, const Value & v)
 }
 
 
+const Value *getPrimOp(const Value &v) {
+    const Value * primOp = &v;
+    while (primOp->type == tPrimOpApp) {
+        primOp = primOp->primOpApp.left;
+    }
+    assert(primOp->type == tPrimOp);
+    return primOp;
+}
+
+
 string showType(const Value & v)
 {
     switch (v.type) {
@@ -145,8 +155,10 @@ string showType(const Value & v)
         case tApp: return "a function application";
         case tLambda: return "a function";
         case tBlackhole: return "a black hole";
-        case tPrimOp: return "a built-in function";
-        case tPrimOpApp: return "a partially applied built-in function";
+        case tPrimOp:
+            return fmt("the built-in function '%s'", string(v.primOp->name));
+        case tPrimOpApp:
+            return fmt("the partially applied built-in function '%s'", string(getPrimOp(v)->primOp->name));
         case tExternal: return v.external->showType();
         case tFloat: return "a float";
     }
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 35c01b97a..95431e6a4 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -327,6 +327,9 @@ private:
 /* Return a string representing the type of the value `v'. */
 string showType(const Value & v);
 
+/* Decode a context string ‘!<name>!<path>’ into a pair <path,
+   name>. */
+std::pair<string, string> decodeContext(const string & s);
 
 /* If `path' refers to a directory, then append "/default.nix". */
 Path resolveExprPath(Path path);
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 7e3dd23ed..080bbf5b5 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -315,6 +315,12 @@ static void prim_isBool(EvalState & state, const Pos & pos, Value * * args, Valu
     mkBool(v, args[0]->type == tBool);
 }
 
+/* Determine whether the argument is a path. */
+static void prim_isPath(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tPath);
+}
 
 struct CompareValues
 {
@@ -687,21 +693,12 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
             }
         }
 
-        /* See prim_unsafeDiscardOutputDependency. */
-        else if (path.at(0) == '~')
-            drv.inputSrcs.insert(string(path, 1));
-
         /* Handle derivation outputs of the form ‘!<name>!<path>’. */
         else if (path.at(0) == '!') {
             std::pair<string, string> ctx = decodeContext(path);
             drv.inputDrvs[ctx.first].insert(ctx.second);
         }
 
-        /* Handle derivation contexts returned by
-           ‘builtins.storePath’. */
-        else if (isDerivation(path))
-            drv.inputDrvs[path] = state.store->queryDerivationOutputNames(path);
-
         /* Otherwise it's a source file. */
         else
             drv.inputSrcs.insert(path);
@@ -1004,13 +1001,8 @@ static void prim_toFile(EvalState & state, const Pos & pos, Value * * args, Valu
     PathSet refs;
 
     for (auto path : context) {
-        if (path.at(0) == '=') path = string(path, 1);
-        if (isDerivation(path)) {
-            /* See prim_unsafeDiscardOutputDependency. */
-            if (path.at(0) != '~')
-                throw EvalError(format("in 'toFile': the file '%1%' cannot refer to derivation outputs, at %2%") % name % pos);
-            path = string(path, 1);
-        }
+        if (path.at(0) != '/')
+            throw EvalError(format("in 'toFile': the file '%1%' cannot refer to derivation outputs, at %2%") % name % pos);
         refs.insert(path);
     }
 
@@ -1794,41 +1786,6 @@ static void prim_stringLength(EvalState & state, const Pos & pos, Value * * args
 }
 
 
-static void prim_unsafeDiscardStringContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
-{
-    PathSet context;
-    string s = state.coerceToString(pos, *args[0], context);
-    mkString(v, s, PathSet());
-}
-
-
-static void prim_hasContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
-{
-    PathSet context;
-    state.forceString(*args[0], context, pos);
-    mkBool(v, !context.empty());
-}
-
-
-/* Sometimes we want to pass a derivation path (i.e. pkg.drvPath) to a
-   builder without causing the derivation to be built (for instance,
-   in the derivation that builds NARs in nix-push, when doing
-   source-only deployment).  This primop marks the string context so
-   that builtins.derivation adds the path to drv.inputSrcs rather than
-   drv.inputDrvs. */
-static void prim_unsafeDiscardOutputDependency(EvalState & state, const Pos & pos, Value * * args, Value & v)
-{
-    PathSet context;
-    string s = state.coerceToString(pos, *args[0], context);
-
-    PathSet context2;
-    for (auto & p : context)
-        context2.insert(p.at(0) == '=' ? "~" + string(p, 1) : p);
-
-    mkString(v, s, context2);
-}
-
-
 /* Return the cryptographic hash of a string in base-16. */
 static void prim_hashString(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
@@ -2218,6 +2175,7 @@ void EvalState::createBaseEnv()
     addPrimOp("__isInt", 1, prim_isInt);
     addPrimOp("__isFloat", 1, prim_isFloat);
     addPrimOp("__isBool", 1, prim_isBool);
+    addPrimOp("__isPath", 1, prim_isPath);
     addPrimOp("__genericClosure", 1, prim_genericClosure);
     addPrimOp("abort", 1, prim_abort);
     addPrimOp("__addErrorContext", 2, prim_addErrorContext);
@@ -2299,9 +2257,6 @@ void EvalState::createBaseEnv()
     addPrimOp("toString", 1, prim_toString);
     addPrimOp("__substring", 3, prim_substring);
     addPrimOp("__stringLength", 1, prim_stringLength);
-    addPrimOp("__hasContext", 1, prim_hasContext);
-    addPrimOp("__unsafeDiscardStringContext", 1, prim_unsafeDiscardStringContext);
-    addPrimOp("__unsafeDiscardOutputDependency", 1, prim_unsafeDiscardOutputDependency);
     addPrimOp("__hashString", 2, prim_hashString);
     addPrimOp("__match", 2, prim_match);
     addPrimOp("__split", 2, prim_split);
diff --git a/src/libexpr/primops/context.cc b/src/libexpr/primops/context.cc
new file mode 100644
index 000000000..2d79739ea
--- /dev/null
+++ b/src/libexpr/primops/context.cc
@@ -0,0 +1,187 @@
+#include "primops.hh"
+#include "eval-inline.hh"
+#include "derivations.hh"
+
+namespace nix {
+
+static void prim_unsafeDiscardStringContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    PathSet context;
+    string s = state.coerceToString(pos, *args[0], context);
+    mkString(v, s, PathSet());
+}
+
+static RegisterPrimOp r1("__unsafeDiscardStringContext", 1, prim_unsafeDiscardStringContext);
+
+
+static void prim_hasContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    PathSet context;
+    state.forceString(*args[0], context, pos);
+    mkBool(v, !context.empty());
+}
+
+static RegisterPrimOp r2("__hasContext", 1, prim_hasContext);
+
+
+/* Sometimes we want to pass a derivation path (i.e. pkg.drvPath) to a
+   builder without causing the derivation to be built (for instance,
+   in the derivation that builds NARs in nix-push, when doing
+   source-only deployment).  This primop marks the string context so
+   that builtins.derivation adds the path to drv.inputSrcs rather than
+   drv.inputDrvs. */
+static void prim_unsafeDiscardOutputDependency(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    PathSet context;
+    string s = state.coerceToString(pos, *args[0], context);
+
+    PathSet context2;
+    for (auto & p : context)
+        context2.insert(p.at(0) == '=' ? string(p, 1) : p);
+
+    mkString(v, s, context2);
+}
+
+static RegisterPrimOp r3("__unsafeDiscardOutputDependency", 1, prim_unsafeDiscardOutputDependency);
+
+
+/* Extract the context of a string as a structured Nix value.
+
+   The context is represented as an attribute set whose keys are the
+   paths in the context set and whose values are attribute sets with
+   the following keys:
+     path: True if the relevant path is in the context as a plain store
+           path (i.e. the kind of context you get when interpolating
+           a Nix path (e.g. ./.) into a string). False if missing.
+     allOutputs: True if the relevant path is a derivation and it is
+                  in the context as a drv file with all of its outputs
+                  (i.e. the kind of context you get when referencing
+                  .drvPath of some derivation). False if missing.
+     outputs: If a non-empty list, the relevant path is a derivation
+              and the provided outputs are referenced in the context
+              (i.e. the kind of context you get when referencing
+              .outPath of some derivation). Empty list if missing.
+   Note that for a given path any combination of the above attributes
+   may be present.
+*/
+static void prim_getContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    struct ContextInfo {
+        bool path = false;
+        bool allOutputs = false;
+        Strings outputs;
+    };
+    PathSet context;
+    state.forceString(*args[0], context, pos);
+    auto contextInfos = std::map<Path, ContextInfo>();
+    for (const auto & p : context) {
+        Path drv;
+        string output;
+        const Path * path = &p;
+        if (p.at(0) == '=') {
+            drv = string(p, 1);
+            path = &drv;
+        } else if (p.at(0) == '!') {
+            std::pair<string, string> ctx = decodeContext(p);
+            drv = ctx.first;
+            output = ctx.second;
+            path = &drv;
+        }
+        auto isPath = drv.empty();
+        auto isAllOutputs = (!drv.empty()) && output.empty();
+
+        auto iter = contextInfos.find(*path);
+        if (iter == contextInfos.end()) {
+            contextInfos.emplace(*path, ContextInfo{isPath, isAllOutputs, output.empty() ? Strings{} : Strings{std::move(output)}});
+        } else {
+            if (isPath)
+                iter->second.path = true;
+            else if (isAllOutputs)
+                iter->second.allOutputs = true;
+            else
+                iter->second.outputs.emplace_back(std::move(output));
+        }
+    }
+
+    state.mkAttrs(v, contextInfos.size());
+
+    auto sPath = state.symbols.create("path");
+    auto sAllOutputs = state.symbols.create("allOutputs");
+    for (const auto & info : contextInfos) {
+        auto & infoVal = *state.allocAttr(v, state.symbols.create(info.first));
+        state.mkAttrs(infoVal, 3);
+        if (info.second.path)
+            mkBool(*state.allocAttr(infoVal, sPath), true);
+        if (info.second.allOutputs)
+            mkBool(*state.allocAttr(infoVal, sAllOutputs), true);
+        if (!info.second.outputs.empty()) {
+            auto & outputsVal = *state.allocAttr(infoVal, state.sOutputs);
+            state.mkList(outputsVal, info.second.outputs.size());
+            size_t i = 0;
+            for (const auto & output : info.second.outputs) {
+                mkString(*(outputsVal.listElems()[i++] = state.allocValue()), output);
+            }
+        }
+        infoVal.attrs->sort();
+    }
+    v.attrs->sort();
+}
+
+static RegisterPrimOp r4("__getContext", 1, prim_getContext);
+
+
+/* Append the given context to a given string.
+
+   See the commentary above unsafeGetContext for details of the
+   context representation.
+*/
+static void prim_appendContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    PathSet context;
+    auto orig = state.forceString(*args[0], context, pos);
+
+    state.forceAttrs(*args[1], pos);
+
+    auto sPath = state.symbols.create("path");
+    auto sAllOutputs = state.symbols.create("allOutputs");
+    for (auto & i : *args[1]->attrs) {
+        if (!state.store->isStorePath(i.name))
+            throw EvalError("Context key '%s' is not a store path, at %s", i.name, i.pos);
+        if (!settings.readOnlyMode)
+            state.store->ensurePath(i.name);
+        state.forceAttrs(*i.value, *i.pos);
+        auto iter = i.value->attrs->find(sPath);
+        if (iter != i.value->attrs->end()) {
+            if (state.forceBool(*iter->value, *iter->pos))
+                context.insert(i.name);
+        }
+
+        iter = i.value->attrs->find(sAllOutputs);
+        if (iter != i.value->attrs->end()) {
+            if (state.forceBool(*iter->value, *iter->pos)) {
+                if (!isDerivation(i.name)) {
+                    throw EvalError("Tried to add all-outputs context of %s, which is not a derivation, to a string, at %s", i.name, i.pos);
+                }
+                context.insert("=" + string(i.name));
+            }
+        }
+
+        iter = i.value->attrs->find(state.sOutputs);
+        if (iter != i.value->attrs->end()) {
+            state.forceList(*iter->value, *iter->pos);
+            if (iter->value->listSize() && !isDerivation(i.name)) {
+                throw EvalError("Tried to add derivation output context of %s, which is not a derivation, to a string, at %s", i.name, i.pos);
+            }
+            for (unsigned int n = 0; n < iter->value->listSize(); ++n) {
+                auto name = state.forceStringNoCtx(*iter->value->listElems()[n], *iter->pos);
+                context.insert("!" + name + "!" + string(i.name));
+            }
+        }
+    }
+
+    mkString(v, orig, context);
+}
+
+static RegisterPrimOp r5("__appendContext", 2, prim_appendContext);
+
+}
diff --git a/src/libstore/download.cc b/src/libstore/download.cc
index 360d48b09..cb77cdc77 100644
--- a/src/libstore/download.cc
+++ b/src/libstore/download.cc
@@ -614,6 +614,22 @@ struct CurlDownloader : public Downloader
         writeFull(wakeupPipe.writeSide.get(), " ");
     }
 
+#ifdef ENABLE_S3
+    std::tuple<std::string, std::string, Store::Params> parseS3Uri(std::string uri)
+    {
+        auto [path, params] = splitUriAndParams(uri);
+
+        auto slash = path.find('/', 5); // 5 is the length of "s3://" prefix
+            if (slash == std::string::npos)
+                throw nix::Error("bad S3 URI '%s'", path);
+
+        std::string bucketName(path, 5, slash - 5);
+        std::string key(path, slash + 1);
+
+        return {bucketName, key, params};
+    }
+#endif
+
     void enqueueDownload(const DownloadRequest & request,
         Callback<DownloadResult> callback) override
     {
@@ -622,12 +638,15 @@ struct CurlDownloader : public Downloader
             // FIXME: do this on a worker thread
             try {
 #ifdef ENABLE_S3
-                S3Helper s3Helper("", Aws::Region::US_EAST_1, "", ""); // FIXME: make configurable
-                auto slash = request.uri.find('/', 5);
-                if (slash == std::string::npos)
-                    throw nix::Error("bad S3 URI '%s'", request.uri);
-                std::string bucketName(request.uri, 5, slash - 5);
-                std::string key(request.uri, slash + 1);
+                auto [bucketName, key, params] = parseS3Uri(request.uri);
+
+                std::string profile = get(params, "profile", "");
+                std::string region = get(params, "region", Aws::Region::US_EAST_1);
+                std::string scheme = get(params, "scheme", "");
+                std::string endpoint = get(params, "endpoint", "");
+
+                S3Helper s3Helper(profile, region, scheme, endpoint);
+
                 // FIXME: implement ETag
                 auto s3Res = s3Helper.getObject(bucketName, key);
                 DownloadResult res;
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index b415d5421..d8a5da0d4 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -129,8 +129,8 @@ Path LocalFSStore::addPermRoot(const Path & _storePath,
        check if the root is in a directory in or linked from the
        gcroots directory. */
     if (settings.checkRootReachability) {
-        Roots roots = findRoots();
-        if (roots.find(gcRoot) == roots.end())
+        Roots roots = findRoots(false);
+        if (roots[storePath].count(gcRoot) == 0)
             printError(
                 format(
                     "warning: '%1%' is not in a directory where the garbage collector looks for roots; "
@@ -197,10 +197,11 @@ void LocalStore::addTempRoot(const Path & path)
 }
 
 
-std::set<std::pair<pid_t, Path>> LocalStore::readTempRoots(FDs & fds)
-{
-    std::set<std::pair<pid_t, Path>> tempRoots;
+static std::string censored = "{censored}";
+
 
+void LocalStore::findTempRoots(FDs & fds, Roots & tempRoots, bool censor)
+{
     /* Read the `temproots' directory for per-process temporary root
        files. */
     for (auto & i : readDirectory(tempRootsDir)) {
@@ -250,14 +251,12 @@ std::set<std::pair<pid_t, Path>> LocalStore::readTempRoots(FDs & fds)
             Path root(contents, pos, end - pos);
             debug("got temporary root '%s'", root);
             assertStorePath(root);
-            tempRoots.emplace(pid, root);
+            tempRoots[root].emplace(censor ? censored : fmt("{temp:%d}", pid));
             pos = end + 1;
         }
 
         fds.push_back(fd); /* keep open */
     }
-
-    return tempRoots;
 }
 
 
@@ -266,7 +265,7 @@ void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
     auto foundRoot = [&](const Path & path, const Path & target) {
         Path storePath = toStorePath(target);
         if (isStorePath(storePath) && isValidPath(storePath))
-            roots[path] = storePath;
+            roots[storePath].emplace(path);
         else
             printInfo(format("skipping invalid root from '%1%' to '%2%'") % path % storePath);
     };
@@ -306,7 +305,7 @@ void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
         else if (type == DT_REG) {
             Path storePath = storeDir + "/" + baseNameOf(path);
             if (isStorePath(storePath) && isValidPath(storePath))
-                roots[path] = storePath;
+                roots[storePath].emplace(path);
         }
 
     }
@@ -321,10 +320,8 @@ void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
 }
 
 
-Roots LocalStore::findRootsNoTemp()
+void LocalStore::findRootsNoTemp(Roots & roots, bool censor)
 {
-    Roots roots;
-
     /* Process direct roots in {gcroots,profiles}. */
     findRoots(stateDir + "/" + gcRootsDir, DT_UNKNOWN, roots);
     findRoots(stateDir + "/profiles", DT_UNKNOWN, roots);
@@ -333,32 +330,22 @@ Roots LocalStore::findRootsNoTemp()
        NIX_ROOT_FINDER environment variable.  This is typically used
        to add running programs to the set of roots (to prevent them
        from being garbage collected). */
-    size_t n = 0;
-    for (auto & root : findRuntimeRoots())
-        roots[fmt("{memory:%d}", n++)] = root;
-
-    return roots;
+    findRuntimeRoots(roots, censor);
 }
 
 
-Roots LocalStore::findRoots()
+Roots LocalStore::findRoots(bool censor)
 {
-    Roots roots = findRootsNoTemp();
+    Roots roots;
+    findRootsNoTemp(roots, censor);
 
     FDs fds;
-    pid_t prev = -1;
-    size_t n = 0;
-    for (auto & root : readTempRoots(fds)) {
-        if (prev != root.first) n = 0;
-        prev = root.first;
-        roots[fmt("{temp:%d:%d}", root.first, n++)] = root.second;
-    }
+    findTempRoots(fds, roots, censor);
 
     return roots;
 }
 
-
-static void readProcLink(const string & file, StringSet & paths)
+static void readProcLink(const string & file, Roots & roots)
 {
     /* 64 is the starting buffer size gnu readlink uses... */
     auto bufsiz = ssize_t{64};
@@ -377,8 +364,8 @@ try_again:
         goto try_again;
     }
     if (res > 0 && buf[0] == '/')
-        paths.emplace(static_cast<char *>(buf), res);
-    return;
+        roots[std::string(static_cast<char *>(buf), res)]
+            .emplace(file);
 }
 
 static string quoteRegexChars(const string & raw)
@@ -387,20 +374,20 @@ static string quoteRegexChars(const string & raw)
     return std::regex_replace(raw, specialRegex, R"(\$&)");
 }
 
-static void readFileRoots(const char * path, StringSet & paths)
+static void readFileRoots(const char * path, Roots & roots)
 {
     try {
-        paths.emplace(readFile(path));
+        roots[readFile(path)].emplace(path);
     } catch (SysError & e) {
         if (e.errNo != ENOENT && e.errNo != EACCES)
             throw;
     }
 }
 
-PathSet LocalStore::findRuntimeRoots()
+void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
 {
-    PathSet roots;
-    StringSet paths;
+    Roots unchecked;
+
     auto procDir = AutoCloseDir{opendir("/proc")};
     if (procDir) {
         struct dirent * ent;
@@ -410,10 +397,10 @@ PathSet LocalStore::findRuntimeRoots()
         while (errno = 0, ent = readdir(procDir.get())) {
             checkInterrupt();
             if (std::regex_match(ent->d_name, digitsRegex)) {
-                readProcLink((format("/proc/%1%/exe") % ent->d_name).str(), paths);
-                readProcLink((format("/proc/%1%/cwd") % ent->d_name).str(), paths);
+                readProcLink(fmt("/proc/%s/exe" ,ent->d_name), unchecked);
+                readProcLink(fmt("/proc/%s/cwd", ent->d_name), unchecked);
 
-                auto fdStr = (format("/proc/%1%/fd") % ent->d_name).str();
+                auto fdStr = fmt("/proc/%s/fd", ent->d_name);
                 auto fdDir = AutoCloseDir(opendir(fdStr.c_str()));
                 if (!fdDir) {
                     if (errno == ENOENT || errno == EACCES)
@@ -422,9 +409,8 @@ PathSet LocalStore::findRuntimeRoots()
                 }
                 struct dirent * fd_ent;
                 while (errno = 0, fd_ent = readdir(fdDir.get())) {
-                    if (fd_ent->d_name[0] != '.') {
-                        readProcLink((format("%1%/%2%") % fdStr % fd_ent->d_name).str(), paths);
-                    }
+                    if (fd_ent->d_name[0] != '.')
+                        readProcLink(fmt("%s/%s", fdStr, fd_ent->d_name), unchecked);
                 }
                 if (errno) {
                     if (errno == ESRCH)
@@ -434,18 +420,19 @@ PathSet LocalStore::findRuntimeRoots()
                 fdDir.reset();
 
                 try {
-                    auto mapLines =
-                        tokenizeString<std::vector<string>>(readFile((format("/proc/%1%/maps") % ent->d_name).str(), true), "\n");
-                    for (const auto& line : mapLines) {
+                    auto mapFile = fmt("/proc/%s/maps", ent->d_name);
+                    auto mapLines = tokenizeString<std::vector<string>>(readFile(mapFile, true), "\n");
+                    for (const auto & line : mapLines) {
                         auto match = std::smatch{};
                         if (std::regex_match(line, match, mapRegex))
-                            paths.emplace(match[1]);
+                            unchecked[match[1]].emplace(mapFile);
                     }
 
-                    auto envString = readFile((format("/proc/%1%/environ") % ent->d_name).str(), true);
+                    auto envFile = fmt("/proc/%s/environ", ent->d_name);
+                    auto envString = readFile(envFile, true);
                     auto env_end = std::sregex_iterator{};
                     for (auto i = std::sregex_iterator{envString.begin(), envString.end(), storePathRegex}; i != env_end; ++i)
-                        paths.emplace(i->str());
+                        unchecked[i->str()].emplace(envFile);
                 } catch (SysError & e) {
                     if (errno == ENOENT || errno == EACCES || errno == ESRCH)
                         continue;
@@ -465,7 +452,7 @@ PathSet LocalStore::findRuntimeRoots()
         for (const auto & line : lsofLines) {
             std::smatch match;
             if (std::regex_match(line, match, lsofRegex))
-                paths.emplace(match[1]);
+                unchecked[match[1]].emplace("{lsof}");
         }
     } catch (ExecError & e) {
         /* lsof not installed, lsof failed */
@@ -473,21 +460,23 @@ PathSet LocalStore::findRuntimeRoots()
 #endif
 
 #if defined(__linux__)
-    readFileRoots("/proc/sys/kernel/modprobe", paths);
-    readFileRoots("/proc/sys/kernel/fbsplash", paths);
-    readFileRoots("/proc/sys/kernel/poweroff_cmd", paths);
+    readFileRoots("/proc/sys/kernel/modprobe", unchecked);
+    readFileRoots("/proc/sys/kernel/fbsplash", unchecked);
+    readFileRoots("/proc/sys/kernel/poweroff_cmd", unchecked);
 #endif
 
-    for (auto & i : paths)
-        if (isInStore(i)) {
-            Path path = toStorePath(i);
-            if (roots.find(path) == roots.end() && isStorePath(path) && isValidPath(path)) {
+    for (auto & [target, links] : unchecked) {
+        if (isInStore(target)) {
+            Path path = toStorePath(target);
+            if (isStorePath(path) && isValidPath(path)) {
                 debug(format("got additional root '%1%'") % path);
-                roots.insert(path);
+                if (censor)
+                    roots[path].insert(censored);
+                else
+                    roots[path].insert(links.begin(), links.end());
             }
         }
-
-    return roots;
+    }
 }
 
 
@@ -754,16 +743,20 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
     /* Find the roots.  Since we've grabbed the GC lock, the set of
        permanent roots cannot increase now. */
     printError(format("finding garbage collector roots..."));
-    Roots rootMap = options.ignoreLiveness ? Roots() : findRootsNoTemp();
+    Roots rootMap;
+    if (!options.ignoreLiveness)
+        findRootsNoTemp(rootMap, true);
 
-    for (auto & i : rootMap) state.roots.insert(i.second);
+    for (auto & i : rootMap) state.roots.insert(i.first);
 
     /* Read the temporary roots.  This acquires read locks on all
        per-process temporary root files.  So after this point no paths
        can be added to the set of temporary roots. */
     FDs fds;
-    for (auto & root : readTempRoots(fds))
-        state.tempRoots.insert(root.second);
+    Roots tempRoots;
+    findTempRoots(fds, tempRoots, true);
+    for (auto & root : tempRoots)
+        state.tempRoots.insert(root.first);
     state.roots.insert(state.tempRoots.begin(), state.tempRoots.end());
 
     /* After this point the set of roots or temporary roots cannot
diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index fce963433..6b655647b 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -180,11 +180,11 @@ private:
     typedef std::shared_ptr<AutoCloseFD> FDPtr;
     typedef list<FDPtr> FDs;
 
-    std::set<std::pair<pid_t, Path>> readTempRoots(FDs & fds);
+    void findTempRoots(FDs & fds, Roots & roots, bool censor);
 
 public:
 
-    Roots findRoots() override;
+    Roots findRoots(bool censor) override;
 
     void collectGarbage(const GCOptions & options, GCResults & results) override;
 
@@ -267,9 +267,9 @@ private:
 
     void findRoots(const Path & path, unsigned char type, Roots & roots);
 
-    Roots findRootsNoTemp();
+    void findRootsNoTemp(Roots & roots, bool censor);
 
-    PathSet findRuntimeRoots();
+    void findRuntimeRoots(Roots & roots, bool censor);
 
     void removeUnusedLinks(const GCState & state);
 
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index def140cfb..15faf78a5 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -596,7 +596,7 @@ void RemoteStore::syncWithGC()
 }
 
 
-Roots RemoteStore::findRoots()
+Roots RemoteStore::findRoots(bool censor)
 {
     auto conn(getConnection());
     conn->to << wopFindRoots;
@@ -606,7 +606,7 @@ Roots RemoteStore::findRoots()
     while (count--) {
         Path link = readString(conn->from);
         Path target = readStorePath(*this, conn->from);
-        result[link] = target;
+        result[target].emplace(link);
     }
     return result;
 }
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
index 919c6d819..80f18ab71 100644
--- a/src/libstore/remote-store.hh
+++ b/src/libstore/remote-store.hh
@@ -82,7 +82,7 @@ public:
 
     void syncWithGC() override;
 
-    Roots findRoots() override;
+    Roots findRoots(bool censor) override;
 
     void collectGarbage(const GCOptions & options, GCResults & results) override;
 
diff --git a/src/libstore/s3-binary-cache-store.cc b/src/libstore/s3-binary-cache-store.cc
index 51de89e0d..cd547a964 100644
--- a/src/libstore/s3-binary-cache-store.cc
+++ b/src/libstore/s3-binary-cache-store.cc
@@ -126,6 +126,7 @@ ref<Aws::Client::ClientConfiguration> S3Helper::makeConfig(const string & region
         res->endpointOverride = endpoint;
     }
     res->requestTimeoutMs = 600 * 1000;
+    res->connectTimeoutMs = 5 * 1000;
     res->retryStrategy = std::make_shared<RetryStrategy>();
     res->caFile = settings.caFile;
     return res;
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 913a11121..c13ff1156 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -842,12 +842,11 @@ namespace nix {
 
 RegisterStoreImplementation::Implementations * RegisterStoreImplementation::implementations = 0;
 
-
-ref<Store> openStore(const std::string & uri_,
-    const Store::Params & extraParams)
+/* Split URI into protocol+hierarchy part and its parameter set. */
+std::pair<std::string, Store::Params> splitUriAndParams(const std::string & uri_)
 {
     auto uri(uri_);
-    Store::Params params(extraParams);
+    Store::Params params;
     auto q = uri.find('?');
     if (q != std::string::npos) {
         for (auto s : tokenizeString<Strings>(uri.substr(q + 1), "&")) {
@@ -873,6 +872,15 @@ ref<Store> openStore(const std::string & uri_,
         }
         uri = uri_.substr(0, q);
     }
+    return {uri, params};
+}
+
+ref<Store> openStore(const std::string & uri_,
+    const Store::Params & extraParams)
+{
+    auto [uri, uriParams] = splitUriAndParams(uri_);
+    auto params = extraParams;
+    params.insert(uriParams.begin(), uriParams.end());
 
     for (auto fun : *RegisterStoreImplementation::implementations) {
         auto store = fun(uri, params);
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index f504735e0..7a1b31d0f 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -11,6 +11,8 @@
 #include <atomic>
 #include <limits>
 #include <map>
+#include <unordered_map>
+#include <unordered_set>
 #include <memory>
 #include <string>
 
@@ -47,7 +49,7 @@ const size_t storePathHashLen = 32; // i.e. 160 bits
 const uint32_t exportMagic = 0x4558494e;
 
 
-typedef std::map<Path, Path> Roots;
+typedef std::unordered_map<Path, std::unordered_set<std::string>> Roots;
 
 
 struct GCOptions
@@ -483,8 +485,10 @@ public:
 
     /* Find the roots of the garbage collector.  Each root is a pair
        (link, storepath) where `link' is the path of the symlink
-       outside of the Nix store that point to `storePath'.  */
-    virtual Roots findRoots()
+       outside of the Nix store that point to `storePath'. If
+       'censor' is true, privacy-sensitive information about roots
+       found in /proc is censored. */
+    virtual Roots findRoots(bool censor)
     { unsupported("findRoots"); }
 
     /* Perform a garbage collection. */
@@ -798,4 +802,8 @@ ValidPathInfo decodeValidPathInfo(std::istream & str,
    for paths created by makeFixedOutputPath() / addToStore(). */
 std::string makeFixedOutputCA(bool recursive, const Hash & hash);
 
+
+/* Split URI into protocol+hierarchy part and its parameter set. */
+std::pair<std::string, Store::Params> splitUriAndParams(const std::string & uri);
+
 }
diff --git a/src/libutil/archive.cc b/src/libutil/archive.cc
index bb68e8288..3aa120270 100644
--- a/src/libutil/archive.cc
+++ b/src/libutil/archive.cc
@@ -331,7 +331,7 @@ struct RestoreSink : ParseSink
                filesystem doesn't support preallocation (e.g. on
                OpenSolaris).  Since preallocation is just an
                optimisation, ignore it. */
-            if (errno && errno != EINVAL)
+            if (errno && errno != EINVAL && errno != EOPNOTSUPP && errno != ENOSYS)
                 throw SysError(format("preallocating file of %1% bytes") % len);
         }
 #endif
diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc
index 8368c3266..8d63b8f36 100644
--- a/src/nix-daemon/nix-daemon.cc
+++ b/src/nix-daemon/nix-daemon.cc
@@ -475,11 +475,19 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
 
     case wopFindRoots: {
         logger->startWork();
-        Roots roots = store->findRoots();
+        Roots roots = store->findRoots(!trusted);
         logger->stopWork();
-        to << roots.size();
+
+        size_t size = 0;
         for (auto & i : roots)
-            to << i.first << i.second;
+            size += i.second.size();
+
+        to << size;
+
+        for (auto & [target, links] : roots)
+            for (auto & link : links)
+                to << link << target;
+
         break;
     }
 
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index a9ad14762..f324056bb 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -427,10 +427,11 @@ static void opQuery(Strings opFlags, Strings opArgs)
                     maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise),
                     referrers, true, settings.gcKeepOutputs, settings.gcKeepDerivations);
             }
-            Roots roots = store->findRoots();
-            for (auto & i : roots)
-                if (referrers.find(i.second) != referrers.end())
-                    cout << format("%1%\n") % i.first;
+            Roots roots = store->findRoots(false);
+            for (auto & [target, links] : roots)
+                if (referrers.find(target) != referrers.end())
+                    for (auto & link : links)
+                        cout << format("%1% -> %2%\n") % link % target;
             break;
         }
 
@@ -485,11 +486,16 @@ static void opReadLog(Strings opFlags, Strings opArgs)
 static void opDumpDB(Strings opFlags, Strings opArgs)
 {
     if (!opFlags.empty()) throw UsageError("unknown flag");
-    if (!opArgs.empty())
-        throw UsageError("no arguments expected");
-    PathSet validPaths = store->queryAllValidPaths();
-    for (auto & i : validPaths)
-        cout << store->makeValidityRegistration({i}, true, true);
+    if (!opArgs.empty()) {
+        for (auto & i : opArgs)
+            i = store->followLinksToStorePath(i);
+        for (auto & i : opArgs)
+            cout << store->makeValidityRegistration({i}, true, true);
+    } else {
+        PathSet validPaths = store->queryAllValidPaths();
+        for (auto & i : validPaths)
+            cout << store->makeValidityRegistration({i}, true, true);
+    }
 }
 
 
@@ -585,9 +591,14 @@ static void opGC(Strings opFlags, Strings opArgs)
     if (!opArgs.empty()) throw UsageError("no arguments expected");
 
     if (printRoots) {
-        Roots roots = store->findRoots();
-        for (auto & i : roots)
-            cout << i.first << " -> " << i.second << std::endl;
+        Roots roots = store->findRoots(false);
+        std::set<std::pair<Path, Path>> roots2;
+        // Transpose and sort the roots.
+        for (auto & [target, links] : roots)
+            for (auto & link : links)
+                roots2.emplace(link, target);
+        for (auto & [link, target] : roots2)
+            std::cout << link << " -> " << target << "\n";
     }
 
     else {