ui: Add Linux section and Journald config to Record new trace page

This adds a new `Linux` section to the `Record new trace` page in the
UI, adding the `linux.journald` datasource as the first section.  In
order to properly allow configuration of the minimum priority to
capture, a `dropdown` widget is added.

Author: staticfloat

ui/src/plugins/dev.perfetto.RecordTraceV2/index.ts

@@ -25,6 +25,7 @@ import {chromeRecordSection} from './pages/chrome';
 import {cpuRecordSection} from './pages/cpu';
 import {gpuRecordSection} from './pages/gpu';
 import {instructionsPage} from './pages/instructions_page';
+import {linuxRecordSection} from './pages/linux';
 import {memoryRecordSection} from './pages/memory';
 import {powerRecordSection} from './pages/power';
 import {RecordPageV2} from './pages/record_page';
@@ -118,6 +119,7 @@ export default class implements PerfettoPlugin {
         gpuRecordSection(),
         powerRecordSection(),
         memoryRecordSection(),
+        linuxRecordSection(),
         androidRecordSection(),
         perfettoSDKRecordSection(),
         stackSamplingRecordSection(),

ui/src/plugins/dev.perfetto.RecordTraceV2/pages/linux.ts

@@ -0,0 +1,89 @@
+// Copyright (C) 2026 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import {RecordProbe, RecordSubpage} from '../config/config_interfaces';
+import {TraceConfigBuilder} from '../config/trace_config_builder';
+import {Dropdown} from './widgets/dropdown';
+import {Textarea} from './widgets/textarea';
+
+const JOURNALD_DS = 'linux.journald';
+
+const MIN_PRIO_OPTIONS = [
+  {value: 0, label: 'EMERG'},
+  {value: 1, label: 'ALERT'},
+  {value: 2, label: 'CRIT'},
+  {value: 3, label: 'ERR'},
+  {value: 4, label: 'WARNING'},
+  {value: 5, label: 'NOTICE'},
+  {value: 6, label: 'INFO'},
+  {value: 7, label: 'DEBUG'},
+] as const;
+
+export function linuxRecordSection(): RecordSubpage {
+  return {
+    kind: 'PROBES_PAGE',
+    id: 'linux',
+    title: 'Linux',
+    subtitle: 'Linux-specific data sources',
+    icon: 'dns',
+    probes: [journald()],
+  };
+}
+
+function journald(): RecordProbe {
+  const settings = {
+    minPrio: new Dropdown<number>({
+      title: 'Minimum syslog priority',
+      options: MIN_PRIO_OPTIONS,
+      defaultValue: 7,
+    }),
+    identifiers: new Textarea({
+      title: 'Process name (SYSLOG_IDENTIFIER) to record',
+      placeholder: 'One identifier per line\nsshd\nmy-service',
+    }),
+    units: new Textarea({
+      title: 'systemd units to record',
+      placeholder:
+        'One unit per line\nsystemd-journald.service\nuser@1000.service',
+    }),
+  };
+
+  return {
+    id: 'journald',
+    title: 'Journald log messages',
+    description: 'Records log messages from systemd-journald.',
+    supportedPlatforms: ['LINUX'],
+    settings,
+    genConfig(tc: TraceConfigBuilder) {
+      const ds = tc.addDataSource(JOURNALD_DS);
+      const journaldConfig = (ds.journaldConfig ??= {});
+      journaldConfig.minPrio = settings.minPrio.value;
+
+      const identifiers = settings.identifiers.text
+        .split('\n')
+        .map((line) => line.trim())
+        .filter((line) => line.length > 0);
+      if (identifiers.length > 0) {
+        journaldConfig.filterIdentifiers = identifiers;
+      }
+      const units = settings.units.text
+        .split('\n')
+        .map((line) => line.trim())
+        .filter((line) => line.length > 0);
+      if (units.length > 0) {
+        journaldConfig.filterUnits = units;
+      }
+    },
+  };
+}

ui/src/plugins/dev.perfetto.RecordTraceV2/pages/record_page.ts

@@ -155,6 +155,7 @@ export class RecordPageV2 implements m.ClassComponent<RecordPageAttrs> {
     memory: 40,
     android: 50,
     network: 60,
+    linux: 65,
     chrome: 70,
     stack_sampling: 80,
     perfetto_sdk: 90,

ui/src/plugins/dev.perfetto.RecordTraceV2/pages/widgets/dropdown.ts

@@ -0,0 +1,82 @@
+// Copyright (C) 2026 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import m from 'mithril';
+import {assertTrue} from '../../../../base/assert';
+import {ProbeSetting} from '../../config/config_interfaces';
+import {Select} from '../../../../widgets/select';
+
+export interface DropdownOption<T extends string | number> {
+  readonly value: T;
+  readonly label: string;
+}
+
+export interface DropdownAttrs<T extends string | number> {
+  readonly title: string;
+  readonly options: ReadonlyArray<DropdownOption<T>>;
+  readonly defaultValue?: T;
+}
+
+export class Dropdown<T extends string | number> implements ProbeSetting {
+  private _value: T;
+
+  constructor(readonly attrs: DropdownAttrs<T>) {
+    assertTrue(attrs.options.length > 0);
+    this._value = attrs.defaultValue ?? attrs.options[0].value;
+  }
+
+  serialize() {
+    return this._value;
+  }
+
+  deserialize(state: unknown): void {
+    if (typeof state !== 'string' && typeof state !== 'number') {
+      return;
+    }
+    const option = this.attrs.options.find(
+      (candidate) => candidate.value === state,
+    );
+    if (option) {
+      this._value = option.value;
+    }
+  }
+
+  get value(): T {
+    return this._value;
+  }
+
+  render() {
+    return m('.textarea-holder', [
+      m('header', this.attrs.title),
+      m(
+        Select,
+        {
+          value: String(this._value),
+          onchange: (e: Event) => {
+            const selectedValue = (e.target as HTMLSelectElement).value;
+            const option = this.attrs.options.find(
+              (candidate) => String(candidate.value) === selectedValue,
+            );
+            if (option) {
+              this._value = option.value;
+            }
+          },
+        },
+        this.attrs.options.map((option) =>
+          m('option', {value: String(option.value)}, option.label),
+        ),
+      ),
+    ]);
+  }
+}