libstore: Create platform LocalStore subclasses

This creates new subclasses of LocalStore for each OS to include
platform-specific functionality. Currently this just includes garbage
collector roots but it could be extended to sandboxing as well.

In order to make sure that the generic LocalStore is not accidentally
constructed, its constructor is protected. A Fallback is provided which
implements no functionality except constructors.

Change-Id: I836a28e90b68309873f75afb83e0f1b2e2c89fb3

src/libstore/gc-store.hh

@@ -7,7 +7,14 @@
 namespace nix {
 
 
+/**
+ * Garbage-collector roots, referring to a store path
+ */
 typedef std::unordered_map<StorePath, std::unordered_set<std::string>> Roots;
+/**
+ * Possible garbage collector roots, referring to any path
+ */
+typedef std::unordered_map<Path, std::unordered_set<std::string>> UncheckedRoots;
 
 
 struct GCOptions

src/libstore/gc.cc

@@ -321,105 +321,8 @@ Roots LocalStore::findRoots(bool censor)
     return roots;
 }
 
-typedef std::unordered_map<Path, std::unordered_set<std::string>> UncheckedRoots;
-
-static void readProcLink(const std::string & file, UncheckedRoots & roots)
+void LocalStore::findPlatformRoots(UncheckedRoots & unchecked)
 {
-    constexpr auto bufsiz = PATH_MAX;
-    char buf[bufsiz];
-    auto res = readlink(file.c_str(), buf, bufsiz);
-    if (res == -1) {
-        if (errno == ENOENT || errno == EACCES || errno == ESRCH)
-            return;
-        throw SysError("reading symlink");
-    }
-    if (res == bufsiz) {
-        throw Error("overly long symlink starting with '%1%'", std::string_view(buf, bufsiz));
-    }
-    if (res > 0 && buf[0] == '/')
-        roots[std::string(static_cast<char *>(buf), res)]
-            .emplace(file);
-}
-
-static std::string quoteRegexChars(const std::string & raw)
-{
-    static auto specialRegex = std::regex(R"([.^$\\*+?()\[\]{}|])");
-    return std::regex_replace(raw, specialRegex, R"(\$&)");
-}
-
-#if __linux__
-static void readFileRoots(const char * path, UncheckedRoots & roots)
-{
-    try {
-        roots[readFile(path)].emplace(path);
-    } catch (SysError & e) {
-        if (e.errNo != ENOENT && e.errNo != EACCES)
-            throw;
-    }
-}
-#endif
-
-void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
-{
-    UncheckedRoots unchecked;
-
-    auto procDir = AutoCloseDir{opendir("/proc")};
-    if (procDir) {
-        struct dirent * ent;
-        auto digitsRegex = std::regex(R"(^\d+$)");
-        auto mapRegex = std::regex(R"(^\s*\S+\s+\S+\s+\S+\s+\S+\s+\S+\s+(/\S+)\s*$)");
-        auto storePathRegex = std::regex(quoteRegexChars(storeDir) + R"(/[0-9a-z]+[0-9a-zA-Z\+\-\._\?=]*)");
-        while (errno = 0, ent = readdir(procDir.get())) {
-            checkInterrupt();
-            if (std::regex_match(ent->d_name, digitsRegex)) {
-                try {
-                    readProcLink(fmt("/proc/%s/exe" ,ent->d_name), unchecked);
-                    readProcLink(fmt("/proc/%s/cwd", ent->d_name), unchecked);
-
-                    auto fdStr = fmt("/proc/%s/fd", ent->d_name);
-                    auto fdDir = AutoCloseDir(opendir(fdStr.c_str()));
-                    if (!fdDir) {
-                        if (errno == ENOENT || errno == EACCES)
-                            continue;
-                        throw SysError("opening %1%", fdStr);
-                    }
-                    struct dirent * fd_ent;
-                    while (errno = 0, fd_ent = readdir(fdDir.get())) {
-                        if (fd_ent->d_name[0] != '.')
-                            readProcLink(fmt("%s/%s", fdStr, fd_ent->d_name), unchecked);
-                    }
-                    if (errno) {
-                        if (errno == ESRCH)
-                            continue;
-                        throw SysError("iterating /proc/%1%/fd", ent->d_name);
-                    }
-                    fdDir.reset();
-
-                    auto mapFile = fmt("/proc/%s/maps", ent->d_name);
-                    auto mapLines = tokenizeString<std::vector<std::string>>(readFile(mapFile), "\n");
-                    for (const auto & line : mapLines) {
-                        auto match = std::smatch{};
-                        if (std::regex_match(line, match, mapRegex))
-                            unchecked[match[1]].emplace(mapFile);
-                    }
-
-                    auto envFile = fmt("/proc/%s/environ", ent->d_name);
-                    auto envString = readFile(envFile);
-                    auto env_end = std::sregex_iterator{};
-                    for (auto i = std::sregex_iterator{envString.begin(), envString.end(), storePathRegex}; i != env_end; ++i)
-                        unchecked[i->str()].emplace(envFile);
-                } catch (SysError & e) {
-                    if (errno == ENOENT || errno == EACCES || errno == ESRCH)
-                        continue;
-                    throw;
-                }
-            }
-        }
-        if (errno)
-            throw SysError("iterating /proc");
-    }
-
-#if !defined(__linux__)
     // lsof is really slow on OS X. This actually causes the gc-concurrent.sh test to fail.
     // See: https://github.com/NixOS/nix/issues/3011
     // Because of this we disable lsof when running the tests.
@@ -437,13 +340,13 @@ void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
             /* lsof not installed, lsof failed */
         }
     }
-#endif
+}
 
-#if __linux__
-    readFileRoots("/proc/sys/kernel/modprobe", unchecked);
-    readFileRoots("/proc/sys/kernel/fbsplash", unchecked);
-    readFileRoots("/proc/sys/kernel/poweroff_cmd", unchecked);
-#endif
+void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
+{
+    UncheckedRoots unchecked;
+
+    findPlatformRoots(unchecked);
 
     for (auto & [target, links] : unchecked) {
         if (!isInStore(target)) continue;

src/libstore/local-store.cc

@@ -1940,6 +1940,4 @@ std::optional<std::string> LocalStore::getVersion()
     return nixVersion;
 }
 
-static RegisterStoreImplementation<LocalStore, LocalStoreConfig> regLocalStore;
-
 }  // namespace nix

src/libstore/local-store.hh

@@ -127,6 +127,17 @@ private:
 
     const PublicKeys & getPublicKeys();
 
+protected:
+
+    /**
+     * Initialise the local store, upgrading the schema if
+     * necessary.
+     * Protected so that users don't accidentally create a LocalStore
+     * instead of a platform's subclass.
+     */
+    LocalStore(const Params & params);
+    LocalStore(std::string scheme, std::string path, const Params & params);
+
 public:
 
     /**
@@ -134,18 +145,16 @@ public:
      */
     PathSet locksHeld;
 
-    /**
-     * Initialise the local store, upgrading the schema if
-     * necessary.
-     */
-    LocalStore(const Params & params);
-    LocalStore(std::string scheme, std::string path, const Params & params);
-
-    ~LocalStore();
+    virtual ~LocalStore();
 
     static std::set<std::string> uriSchemes()
     { return {}; }
 
+    /**
+     * Create a LocalStore, possibly a platform-specific subclass
+     */
+    static std::shared_ptr<LocalStore> makeLocalStore(const Params & params);
+
     /**
      * Implementations of abstract store API methods.
      */
@@ -330,6 +339,12 @@ private:
 
     void findRootsNoTemp(Roots & roots, bool censor);
 
+    /**
+     * Find possible garbage collector roots in a platform-specific manner,
+     * e.g. by looking in `/proc` or using `lsof`
+     */
+    virtual void findPlatformRoots(UncheckedRoots & unchecked);
+
     void findRuntimeRoots(Roots & roots, bool censor);
 
     std::pair<Path, AutoCloseFD> createTempDirInStore();

src/libstore/local.mk

@@ -5,6 +5,11 @@ libstore_NAME = libnixstore
 libstore_DIR := $(d)
 
 libstore_SOURCES := $(wildcard $(d)/*.cc $(d)/builtins/*.cc $(d)/build/*.cc)
+ifdef HOST_LINUX
+libstore_SOURCES += $(d)/platform/linux.cc
+else
+libstore_SOURCES += $(d)/platform/fallback.cc
+endif
 
 libstore_LIBS = libutil
 

src/libstore/meson.build

@@ -66,6 +66,7 @@ libstore_sources = files(
   'path-with-outputs.cc',
   'path.cc',
   'pathlocks.cc',
+  'platform.cc',
   'profiles.cc',
   'realisation.cc',
   'remote-fs-accessor.cc',
@@ -158,6 +159,14 @@ libstore_headers = files(
   'worker-protocol.hh',
 )
 
+if host_machine.system() == 'linux'
+  libstore_sources += files('platform/linux.cc')
+  libstore_headers += files('platform/linux.hh')
+else
+  libstore_sources += files('platform/fallback.cc')
+  libstore_headers += files('platform/fallback.hh')
+endif
+
 # These variables (aside from LSOF) are created pseudo-dynamically, near the beginning of
 # the top-level meson.build. Aside from prefix itself, each of these was
 # made into an absolute path by joining it with prefix, unless it was already

src/libstore/platform.cc

@@ -0,0 +1,18 @@
+#include "local-store.hh"
+
+#if __linux__
+#include "platform/linux.hh"
+#else
+#include "platform/fallback.hh"
+#endif
+
+namespace nix {
+std::shared_ptr<LocalStore> LocalStore::makeLocalStore(const Params & params)
+{
+#if __linux__
+    return std::shared_ptr<LocalStore>(new LinuxLocalStore(params));
+#else
+    return std::shared_ptr<LocalStore>(new FallbackLocalStore(params));
+#endif
+}
+}

src/libstore/platform/fallback.cc

@@ -0,0 +1,5 @@
+#include "platform/fallback.hh"
+
+namespace nix {
+static RegisterStoreImplementation<FallbackLocalStore, LocalStoreConfig> regLocalStore;
+}

src/libstore/platform/fallback.hh

@@ -0,0 +1,31 @@
+#pragma once
+///@file
+
+#include "local-store.hh"
+
+namespace nix {
+
+/**
+ * Fallback platform implementation of LocalStore
+ * Exists so we can make LocalStore constructor protected
+ */
+class FallbackLocalStore : public LocalStore
+{
+public:
+    FallbackLocalStore(const Params & params)
+        : StoreConfig(params)
+        , LocalFSStoreConfig(params)
+        , LocalStoreConfig(params)
+        , Store(params)
+        , LocalFSStore(params)
+        , LocalStore(params)
+    {
+    }
+    FallbackLocalStore(const std::string scheme, std::string path, const Params & params)
+        : FallbackLocalStore(params)
+    {
+        throw UnimplementedError("FallbackLocalStore");
+    }
+};
+
+}

src/libstore/platform/linux.cc

@@ -0,0 +1,123 @@
+#include "gc-store.hh"
+#include "signals.hh"
+#include "platform/linux.hh"
+
+#include <regex>
+
+namespace nix {
+static RegisterStoreImplementation<LinuxLocalStore, LocalStoreConfig> regLocalStore;
+
+static void readProcLink(const std::string & file, UncheckedRoots & roots)
+{
+    constexpr auto bufsiz = PATH_MAX;
+    char buf[bufsiz];
+    auto res = readlink(file.c_str(), buf, bufsiz);
+    if (res == -1) {
+        if (errno == ENOENT || errno == EACCES || errno == ESRCH) {
+            return;
+        }
+        throw SysError("reading symlink");
+    }
+    if (res == bufsiz) {
+        throw Error("overly long symlink starting with '%1%'", std::string_view(buf, bufsiz));
+    }
+    if (res > 0 && buf[0] == '/') {
+        roots[std::string(static_cast<char *>(buf), res)].emplace(file);
+    }
+}
+
+static std::string quoteRegexChars(const std::string & raw)
+{
+    static auto specialRegex = std::regex(R"([.^$\\*+?()\[\]{}|])");
+    return std::regex_replace(raw, specialRegex, R"(\$&)");
+}
+
+static void readFileRoots(const char * path, UncheckedRoots & roots)
+{
+    try {
+        roots[readFile(path)].emplace(path);
+    } catch (SysError & e) {
+        if (e.errNo != ENOENT && e.errNo != EACCES) {
+            throw;
+        }
+    }
+}
+
+void LinuxLocalStore::findPlatformRoots(UncheckedRoots & unchecked)
+{
+    auto procDir = AutoCloseDir{opendir("/proc")};
+    if (procDir) {
+        struct dirent * ent;
+        auto digitsRegex = std::regex(R"(^\d+$)");
+        auto mapRegex = std::regex(R"(^\s*\S+\s+\S+\s+\S+\s+\S+\s+\S+\s+(/\S+)\s*$)");
+        auto storePathRegex =
+            std::regex(quoteRegexChars(storeDir) + R"(/[0-9a-z]+[0-9a-zA-Z\+\-\._\?=]*)");
+        while (errno = 0, ent = readdir(procDir.get())) {
+            checkInterrupt();
+            if (std::regex_match(ent->d_name, digitsRegex)) {
+                try {
+                    readProcLink(fmt("/proc/%s/exe", ent->d_name), unchecked);
+                    readProcLink(fmt("/proc/%s/cwd", ent->d_name), unchecked);
+
+                    auto fdStr = fmt("/proc/%s/fd", ent->d_name);
+                    auto fdDir = AutoCloseDir(opendir(fdStr.c_str()));
+                    if (!fdDir) {
+                        if (errno == ENOENT || errno == EACCES) {
+                            continue;
+                        }
+                        throw SysError("opening %1%", fdStr);
+                    }
+                    struct dirent * fd_ent;
+                    while (errno = 0, fd_ent = readdir(fdDir.get())) {
+                        if (fd_ent->d_name[0] != '.') {
+                            readProcLink(fmt("%s/%s", fdStr, fd_ent->d_name), unchecked);
+                        }
+                    }
+                    if (errno) {
+                        if (errno == ESRCH) {
+                            continue;
+                        }
+                        throw SysError("iterating /proc/%1%/fd", ent->d_name);
+                    }
+                    fdDir.reset();
+
+                    auto mapFile = fmt("/proc/%s/maps", ent->d_name);
+                    auto mapLines =
+                        tokenizeString<std::vector<std::string>>(readFile(mapFile), "\n");
+                    for (const auto & line : mapLines) {
+                        auto match = std::smatch{};
+                        if (std::regex_match(line, match, mapRegex)) {
+                            unchecked[match[1]].emplace(mapFile);
+                        }
+                    }
+
+                    auto envFile = fmt("/proc/%s/environ", ent->d_name);
+                    auto envString = readFile(envFile);
+                    auto env_end = std::sregex_iterator{};
+                    for (auto i =
+                             std::sregex_iterator{
+                                 envString.begin(), envString.end(), storePathRegex
+                             };
+                         i != env_end;
+                         ++i)
+                    {
+                        unchecked[i->str()].emplace(envFile);
+                    }
+                } catch (SysError & e) {
+                    if (errno == ENOENT || errno == EACCES || errno == ESRCH) {
+                        continue;
+                    }
+                    throw;
+                }
+            }
+        }
+        if (errno) {
+            throw SysError("iterating /proc");
+        }
+    }
+
+    readFileRoots("/proc/sys/kernel/modprobe", unchecked);
+    readFileRoots("/proc/sys/kernel/fbsplash", unchecked);
+    readFileRoots("/proc/sys/kernel/poweroff_cmd", unchecked);
+}
+}

src/libstore/platform/linux.hh

@@ -0,0 +1,35 @@
+#pragma once
+///@file
+
+#include "gc-store.hh"
+#include "local-store.hh"
+
+namespace nix {
+
+/**
+ * Linux-specific implementation of LocalStore
+ */
+class LinuxLocalStore : public LocalStore
+{
+public:
+    LinuxLocalStore(const Params & params)
+        : StoreConfig(params)
+        , LocalFSStoreConfig(params)
+        , LocalStoreConfig(params)
+        , Store(params)
+        , LocalFSStore(params)
+        , LocalStore(params)
+    {
+    }
+    LinuxLocalStore(const std::string scheme, std::string path, const Params & params)
+        : LinuxLocalStore(params)
+    {
+        throw UnimplementedError("LinuxLocalStore");
+    }
+
+private:
+
+    void findPlatformRoots(UncheckedRoots & unchecked) override;
+};
+
+}

src/libstore/store-api.cc

@@ -1426,7 +1426,7 @@ std::shared_ptr<Store> openFromNonUri(const std::string & uri, const Store::Para
     if (uri == "" || uri == "auto") {
         auto stateDir = getOr(params, "state", settings.nixStateDir);
         if (access(stateDir.c_str(), R_OK | W_OK) == 0)
-            return std::make_shared<LocalStore>(params);
+            return LocalStore::makeLocalStore(params);
         else if (pathExists(settings.nixDaemonSocketFile))
             return std::make_shared<UDSRemoteStore>(params);
         #if __linux__
@@ -1444,26 +1444,26 @@ std::shared_ptr<Store> openFromNonUri(const std::string & uri, const Store::Para
                 try {
                     createDirs(chrootStore);
                 } catch (Error & e) {
-                    return std::make_shared<LocalStore>(params);
+                    return LocalStore::makeLocalStore(params);
                 }
                 warn("'%s' does not exist, so Nix will use '%s' as a chroot store", stateDir, chrootStore);
             } else
                 debug("'%s' does not exist, so Nix will use '%s' as a chroot store", stateDir, chrootStore);
             Store::Params params2;
             params2["root"] = chrootStore;
-            return std::make_shared<LocalStore>(params2);
+            return LocalStore::makeLocalStore(params);
         }
         #endif
         else
-            return std::make_shared<LocalStore>(params);
+            return LocalStore::makeLocalStore(params);
     } else if (uri == "daemon") {
         return std::make_shared<UDSRemoteStore>(params);
     } else if (uri == "local") {
-        return std::make_shared<LocalStore>(params);
+        return LocalStore::makeLocalStore(params);
     } else if (isNonUriPath(uri)) {
         Store::Params params2 = params;
         params2["root"] = absPath(uri);
-        return std::make_shared<LocalStore>(params2);
+        return LocalStore::makeLocalStore(params2);
     } else {
         return nullptr;
     }