feat(libstore): add page size system feature

doc/manual/source/language/advanced-attributes.md

@@ -370,6 +370,18 @@ Derivations can declare some infrequently used optional attributes.
 
   ensures that the derivation can only be built on a machine with the `kvm` feature.
 
+- [`rejectSystemFeatures`]{#adv-attr-rejectSystemFeatures}\
+
+  If a derivation has the `rejectSystemFeatures` attribute, then Nix will only build it on a machine that does not have the corresponding features set in its [`system-features` configuration](@docroot@/command-ref/conf-file.md#conf-system-features).
+
+  For example, setting
+
+  ```nix
+  rejectSystemFeatures = [ "pages-16k" ];
+  ```
+
+  ensures that the derivation can only be built on a machine which does not have the `pages-16k` feature.
+
 [xp-feature-ca-derivations]: @docroot@/development/experimental-features.md#xp-feature-ca-derivations
 [xp-feature-dynamic-derivations]: @docroot@/development/experimental-features.md#xp-feature-dynamic-derivations
 [xp-feature-git-hashing]: @docroot@/development/experimental-features.md#xp-feature-git-hashing

src/libstore/derivation-options.cc

@@ -134,6 +134,7 @@ DerivationOptions DerivationOptions::fromParsedDerivation(const ParsedDerivation
         .allowLocalNetworking = parsed.getBoolAttr("__darwinAllowLocalNetworking", defaults.allowLocalNetworking),
         .requiredSystemFeatures =
             parsed.getStringSetAttr("requiredSystemFeatures").value_or(defaults.requiredSystemFeatures),
+        .rejectSystemFeatures = parsed.getStringSetAttr("rejectSystemFeatures").value_or(defaults.rejectSystemFeatures),
         .preferLocalBuild = parsed.getBoolAttr("preferLocalBuild", defaults.preferLocalBuild),
         .allowSubstitutes = parsed.getBoolAttr("allowSubstitutes", defaults.allowSubstitutes),
     };
@@ -150,6 +151,15 @@ StringSet DerivationOptions::getRequiredSystemFeatures(const BasicDerivation & d
     return res;
 }
 
+StringSet DerivationOptions::getRejectSystemFeatures(const BasicDerivation & drv) const
+{
+    // FIXME: cache this?
+    StringSet res;
+    for (auto & i : rejectSystemFeatures)
+        res.insert(i);
+    return res;
+}
+
 bool DerivationOptions::canBuildLocally(Store & localStore, const BasicDerivation & drv) const
 {
     if (drv.platform != settings.thisSystem.get() && !settings.extraPlatforms.get().count(drv.platform)
@@ -215,6 +225,7 @@ DerivationOptions adl_serializer<DerivationOptions>::from_json(const json & json
         .allowLocalNetworking = getBoolean(valueAt(json, "allowLocalNetworking")),
 
         .requiredSystemFeatures = getStringSet(valueAt(json, "requiredSystemFeatures")),
+        .rejectSystemFeatures = getStringSet(valueAt(json, "rejectSystemFeatures")),
         .preferLocalBuild = getBoolean(valueAt(json, "preferLocalBuild")),
         .allowSubstitutes = getBoolean(valueAt(json, "allowSubstitutes")),
     };
@@ -247,6 +258,7 @@ void adl_serializer<DerivationOptions>::to_json(json & json, DerivationOptions o
     json["allowLocalNetworking"] = o.allowLocalNetworking;
 
     json["requiredSystemFeatures"] = o.requiredSystemFeatures;
+    json["rejectSystemFeatures"] = o.rejectSystemFeatures;
     json["preferLocalBuild"] = o.preferLocalBuild;
     json["allowSubstitutes"] = o.allowSubstitutes;
 }

src/libstore/derivation-options.hh

@@ -134,6 +134,11 @@ struct DerivationOptions
      */
     StringSet requiredSystemFeatures = {};
 
+    /**
+     * env: rejectSystemFeatures
+     */
+    StringSet rejectSystemFeatures = {};
+
     /**
      * env: preferLocalBuild
      */
@@ -161,6 +166,11 @@ struct DerivationOptions
      */
     StringSet getRequiredSystemFeatures(const BasicDerivation & drv) const;
 
+    /**
+     * @param drv See note on `getRequiredSystemFeatures`
+     */
+    StringSet getRejectSystemFeatures(const BasicDerivation & drv) const;
+
     /**
      * @param drv See note on `getRequiredSystemFeatures`
      */

src/libstore/globals.cc

@@ -174,6 +174,8 @@ static bool hasVirt() {
 }
 #endif
 
+extern "C" const char** nix_libstore_get_default_system_features();
+
 StringSet Settings::getDefaultSystemFeatures()
 {
     /* For backwards compatibility, accept some "features" that are
@@ -195,6 +197,14 @@ StringSet Settings::getDefaultSystemFeatures()
         features.insert("apple-virt");
     #endif
 
+    const char** value = nix_libstore_get_default_system_features();
+    if (value != nullptr) {
+        for (size_t i = 0; value[i] != nullptr; i++) {
+            features.insert(value[i]);
+        }
+    }
+    free(value);
+
     return features;
 }
 

src/libstore/globals.hh

@@ -304,7 +304,7 @@ public:
 
           6. A comma-separated list of supported [system features](#conf-system-features).
 
-             A machine will only be used to build a derivation if all the features in the derivation's [`requiredSystemFeatures`](@docroot@/language/advanced-attributes.html#adv-attr-requiredSystemFeatures) attribute are supported by that machine.
+             A machine will only be used to build a derivation if all the features in the derivation's [`requiredSystemFeatures`](@docroot@/language/advanced-attributes.html#adv-attr-requiredSystemFeatures) attribute are supported by that machine and does not have any features in [`rejectSystemFeatures`](@docroot@/language/advanced-attributes.html#adv-attr-rejectSystemFeatures).
 
           7. A comma-separated list of required [system features](#conf-system-features).
 

src/libstore/globals.zig

@@ -0,0 +1,23 @@
+const std = @import("std");
+
+pub fn getDefaultSystemFeatures() callconv(.C) ?[*:null]const ?[*:0]const u8 {
+    var list = std.ArrayList(?[*:0]const u8).init(std.heap.c_allocator);
+    defer list.deinit();
+
+    const pgsize = std.heap.pageSize();
+
+    if (pgsize == std.heap.page_size_max) {
+        list.append(std.fmt.allocPrintZ(std.heap.c_allocator, "pages-{d}k", .{pgsize / 1024}) catch return null) catch return null;
+    } else {
+        var i = pgsize;
+        while (i < std.heap.page_size_max) : (i *= 2) {
+            list.append(std.fmt.allocPrintZ(std.heap.c_allocator, "pages-{d}k", .{i / 1024}) catch return null) catch return null;
+        }
+    }
+
+    return list.toOwnedSliceSentinel(null) catch return null;
+}
+
+comptime {
+    @export(&getDefaultSystemFeatures, .{ .name = "nix_libstore_get_default_system_features" });
+}

src/libstore/libstore.zig

@@ -0,0 +1,5 @@
+pub const globals = @import("globals.zig");
+
+comptime {
+    _ = globals;
+}

src/libstore/meson.build

@@ -1,4 +1,4 @@
-project('nix-store', 'cpp',
+project('nix-store', 'cpp', 'c',
   version : files('.zix-version'),
   default_options : [
     'cpp_std=c++2a',
@@ -132,6 +132,8 @@ if aws_s3.found()
 endif
 deps_other += aws_s3
 
+subdir('nix-meson-build-support/zig')
+
 subdir('nix-meson-build-support/generate-header')
 
 generated_headers = []
@@ -424,6 +426,18 @@ endforeach
 subdir('nix-meson-build-support/export-all-symbols')
 subdir('nix-meson-build-support/windows-version')
 
+sources += custom_target(
+  'zig build-lib',
+  command: [zig, 'build-lib', '-femit-h=@OUTDIR@/libstore-zig.h', '-femit-bin=@OUTPUT@', '-ofmt=c', '-lc', zig_args, '@INPUT@'],
+  output: 'libstore-zig.c',
+  input: 'libstore.zig',
+  depend_files: [
+    'globals.zig',
+  ],
+)
+
+include_dirs += fs.parent(fs.parent(zig.full_path())) / 'lib' / 'zig'
+
 this_library = library(
   'nixstore',
   generated_headers,

src/libstore/package.nix

@@ -50,6 +50,7 @@ mkMesonLibrary (finalAttrs: {
     (fileset.fileFilter (file: file.hasExt "sb") ./.)
     (fileset.fileFilter (file: file.hasExt "md") ./.)
     (fileset.fileFilter (file: file.hasExt "sql") ./.)
+    (fileset.fileFilter (file: file.hasExt "zig") ./.)
   ];
 
   nativeBuildInputs = lib.optional embeddedSandboxShell unixtools.hexdump;

src/libstore/unix/build/local-derivation-goal.cc

@@ -531,9 +531,10 @@ void LocalDerivationGoal::startBuilder()
         if (drv->platform == "x86_64-darwin" && settings.thisSystem == "aarch64-darwin") {
             throw Error("run `/usr/sbin/softwareupdate --install-rosetta` to enable your %s to run programs for %s", settings.thisSystem, drv->platform);
         } else {
-            throw Error("a '%s' with features {%s} is required to build '%s', but I am a '%s' with features {%s}",
+            throw Error("a '%s' with features {%s} & not {%s} is required to build '%s', but I am a '%s' with features {%s}",
                 drv->platform,
                 concatStringsSep(", ", drvOptions->getRequiredSystemFeatures(*drv)),
+                concatStringsSep(", ", drvOptions->getRejectSystemFeatures(*drv)),
                 worker.store.printStorePath(drvPath),
                 settings.thisSystem,
                 concatStringsSep<StringSet>(", ", worker.store.systemFeatures));

tests/functional/build-hook.nix

@@ -69,12 +69,31 @@ let
     requiredSystemFeatures = [ "baz" ];
   };
 
+  input4 = mkDerivation {
+    shell = busybox;
+    name = "build-remote-input-4";
+    buildCommand = ''
+      echo hi-input3
+      read x < ${input3}
+      echo $x BAZ > $out
+    '';
+    rejectSystemFeatures = [ "bar" ];
+    requiredSystemFeatures = [ "foo" ];
+  };
+
 in
 
 mkDerivation {
   shell = busybox;
   name = "build-remote";
-  passthru = { inherit input1 input2 input3; };
+  passthru = {
+    inherit
+      input1
+      input2
+      input3
+      input4
+      ;
+  };
   buildCommand = ''
     read x < ${input1}
     read y < ${input3}

tests/functional/build-remote.sh

@@ -23,6 +23,7 @@ builders=(
   "ssh://localhost?remote-store=$TEST_ROOT/machine1?system-features=$(join_by "%20" foo "${EXTRA_SYSTEM_FEATURES[@]}") - - 1 1 $(join_by "," foo "${EXTRA_SYSTEM_FEATURES[@]}")"
   "$TEST_ROOT/machine2 - - 1 1 $(join_by "," bar "${EXTRA_SYSTEM_FEATURES[@]}")"
   "ssh-ng://localhost?remote-store=$TEST_ROOT/machine3?system-features=$(join_by "%20" baz "${EXTRA_SYSTEM_FEATURES[@]}") - - 1 1 $(join_by "," baz "${EXTRA_SYSTEM_FEATURES[@]}")"
+  "$TEST_ROOT/machine4 - - 1 1 $(join_by "," bar foo "${EXTRA_SYSTEM_FEATURES[@]}")"
 )
 
 chmod -R +w "$TEST_ROOT/machine"* || true
@@ -70,6 +71,12 @@ echo "$output" | grepQuietInverse builder-build-remote-input-2.sh
 echo "$output" | grepQuiet builder-build-remote-input-3.sh
 unset output
 
+# Ensure that input4 was built on store4 due to the required feature.
+output=$(nix path-info --store "$TEST_ROOT/machine4" --all)
+echo "$output" | grepQuietInverse builder-build-remote-input-1.sh
+echo "$output" | grepQuietInverse builder-build-remote-input-2.sh
+echo "$output" | grepQuietInverse builder-build-remote-input-3.sh
+unset output
 
 for i in input1 input3; do
 nix log --store "$TEST_ROOT/machine0" --file "$file" --arg busybox "$busybox" "passthru.$i" | grep hi-$i