init: add MountHandler property handler

Set properties dev.mnt.blk.<mount_point>=<device_block_class> for mount
and umount operations by setting up an Epoll handler to catch
EPOLLERR or EPOLLPRI signals when /proc/mounts is changed.  Only
update properties associated with block devices.  For the mount
point of /, use the designation of /root instead.

Can use the properties in init rc expansion like:

on property dev.mnt.blk.root=*
    write /sys/block/${dev.mnt.blk.root}/queue/read_ahead_kb ${boot_read_ahead_kb:-2048}

on property dev.mnt.blk.data=*
    write /sys/block/${dev.mnt.blk.data}/queue/read_ahead_kb ${boot_read_ahead_kb:-2048}

on late-fs
    setprop boot_read_ahead_kb 128
    write /sys/block/${dev.mnt.blk.root}/queue/read_ahead_kb ${boot_read_ahead_kb}
    write /sys/block/${dev.mnt.blk.data}/queue/read_ahead_kb ${boot_read_ahead_kb}

Test: boot and inspect getprop results.
Bug: 124072565
Change-Id: I1b8aff44f922ba372cd926de2919c215c40ee874

1 files changed, 59 insertions, 0 deletions

diff --git a/init/mount_handler.h b/init/mount_handler.h
new file mode 100644
index 000000000..e524a74ae
--- /dev/null
+++ b/init/mount_handler.h
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2019 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.
+ */
+
+#pragma once
+
+#include <stdio.h>
+
+#include <memory>
+#include <set>
+#include <string>
+
+#include "epoll.h"
+
+namespace android {
+namespace init {
+
+struct MountHandlerEntry {
+    MountHandlerEntry(const std::string& blk_device, const std::string& mount_point,
+                      const std::string& fs_type);
+
+    bool operator<(const MountHandlerEntry& r) const;
+
+    const std::string blk_device;
+    const std::string mount_point;
+    const std::string fs_type;
+};
+
+class MountHandler {
+  public:
+    explicit MountHandler(Epoll* epoll);
+    MountHandler(const MountHandler&) = delete;
+    MountHandler(MountHandler&&) = delete;
+    MountHandler& operator=(const MountHandler&) = delete;
+    MountHandler& operator=(MountHandler&&) = delete;
+    ~MountHandler();
+
+  private:
+    void MountHandlerFunction();
+
+    Epoll* epoll_;
+    std::unique_ptr<FILE, decltype(&fclose)> fp_;
+    std::set<MountHandlerEntry> mounts_;
+};
+
+}  // namespace init
+}  // namespace android