Init: add dev.mnt.blk.bootdevice to access device sysfs

This patch adds a new property, 'dev.mnt.root.<mount_point>', which provides,
for example of /data,

1. dm-N
  dev.mnt.dev.data = dm-N
  dev.mnt.blk.data = sdaN or mmcblk0pN
  dev.mnt.rootdisk.data = sda or mmcblk0

2. sdaN or mmcblk0pN
  dev.mnt.dev.data = sdaN or mmcblk0pN
  dev.mnt.blk.data = sdaN or mmcblk0pN
  dev.mnt.rootdisk.data = sda or mmcblk0

Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
Change-Id: I0a58a62d416f966f26b5de04112c2f9a7eceb22c

init/README.md

@@ -804,13 +804,18 @@ Init provides state information with the following properties.
 `init.svc.<name>`
 > State of a named service ("stopped", "stopping", "running", "restarting")
 
-`dev.mnt.blk.<mount_point>`
+`dev.mnt.dev.<mount_point>`, `dev.mnt.blk.<mount_point>`, `dev.mnt.rootdisk.<mount_point>`
 > Block device base name associated with a *mount_point*.
   The *mount_point* has / replaced by . and if referencing the root mount point
-  "/", it will use "/root", specifically `dev.mnt.blk.root`.
+  "/", it will use "/root".
-  Meant for references to `/sys/device/block/${dev.mnt.blk.<mount_point>}/` and
+  `dev.mnt.dev.<mount_point>` indicates a block device attached to filesystems.
-  `/sys/fs/ext4/${dev.mnt.blk.<mount_point>}/` to tune the block device
+    (e.g., dm-N or sdaN/mmcblk0pN to access `/sys/fs/ext4/${dev.mnt.dev.<mount_point>}/`)
-  characteristics in a device agnostic manner.
+
+  `dev.mnt.blk.<mount_point>` indicates the disk partition to the above block device.
+    (e.g., sdaN / mmcblk0pN to access `/sys/class/block/${dev.mnt.blk.<mount_point>}/`)
+
+  `dev.mnt.rootdisk.<mount_point>` indicates the root disk to contain the above disk partition.
+    (e.g., sda / mmcblk0 to access `/sys/class/block/${dev.mnt.rootdisk.<mount_point>}/queue`)
 
 Init responds to properties that begin with `ctl.`.  These properties take the format of
 `ctl.[<target>_]<command>` and the _value_ of the system property is used as a parameter.  The

init/mount_handler.cpp

@@ -72,8 +72,25 @@ MountHandlerEntry ParseMount(const std::string& line) {
     return MountHandlerEntry(fields[0], fields[1], fields[2]);
 }
 
-// return dm-4 or dm-8 for dm-4, sda for sda25, or mmcblk0 for mmcblk0p24
+// return sda25 for dm-4, sda25 for sda25, or mmcblk0p24 for mmcblk0p24
+std::string GetDiskPart(std::string blockdev) {
+    if (blockdev.find('/') != std::string::npos) return {};
+
+    while (android::base::StartsWith(blockdev, "dm-")) {
+        auto& dm = dm::DeviceMapper::Instance();
+        std::optional<std::string> parent = dm.GetParentBlockDeviceByPath("/dev/block/" + blockdev);
+        if (parent) {
+            blockdev = android::base::Basename(*parent);
+        } else {
+            return {};
+        }
+    }
+    return blockdev;
+}
+
+// return sda for sda25, or mmcblk0 for mmcblk0p24
 std::string GetRootDisk(std::string blockdev) {
+    if (blockdev.empty()) return {};
     if (blockdev.find('/') != std::string::npos) return {};
 
     std::error_code ec;
@@ -83,7 +100,6 @@ std::string GetRootDisk(std::string blockdev) {
             return Basename(path);
         }
     }
-    if (android::base::StartsWith(blockdev, "dm-")) return blockdev;
     return {};
 }
 
@@ -91,31 +107,47 @@ void SetMountProperty(const MountHandlerEntry& entry, bool add) {
     static constexpr char devblock[] = "/dev/block/";
     if (!android::base::StartsWith(entry.blk_device, devblock)) return;
     auto target = entry.blk_device.substr(strlen(devblock));
-    std::string value;
+    std::string diskpart, rootdisk;
     if (add) {
-        value = GetRootDisk(target);
+        diskpart = GetDiskPart(target);
+        rootdisk = GetRootDisk(diskpart);
 
         struct stat sb;
-        if (stat(entry.mount_point.c_str(), &sb) || !S_ISDIR(sb.st_mode)) value = "";
+        if (stat(entry.mount_point.c_str(), &sb) || !S_ISDIR(sb.st_mode)) rootdisk = "";
         // Clear the noise associated with loopback and APEX.
-        if (android::base::StartsWith(value, "loop")) value = "";
+        if (android::base::StartsWith(target, "loop")) rootdisk = "";
-        if (android::base::StartsWith(entry.mount_point, "/apex/")) value = "";
+        if (android::base::StartsWith(entry.mount_point, "/apex/")) rootdisk = "";
     }
     auto mount_prop = entry.mount_point;
     if (mount_prop == "/") mount_prop = "/root";
     std::replace(mount_prop.begin(), mount_prop.end(), '/', '.');
     auto blk_mount_prop = "dev.mnt.blk" + mount_prop;
     auto dev_mount_prop = "dev.mnt.dev" + mount_prop;
-    // Set property even if its value does not change to trigger 'on property:'
+    auto rootdisk_mount_prop = "dev.mnt.rootdisk" + mount_prop;
+    // Set property even if its rootdisk does not change to trigger 'on property:'
     // handling, except for clearing non-existent or already clear property.
     // Goal is reduction of empty properties and associated triggers.
-    if (value.empty() && android::base::GetProperty(blk_mount_prop, "").empty()) return;
+    if (rootdisk.empty() && android::base::GetProperty(blk_mount_prop, "").empty()) return;
-    android::base::SetProperty(blk_mount_prop, value);
+
-    if (!value.empty()) {
+    if (rootdisk.empty()) {
-        android::base::SetProperty(dev_mount_prop, target);
+        android::base::SetProperty(blk_mount_prop, "");
-    } else {
         android::base::SetProperty(dev_mount_prop, "");
+        android::base::SetProperty(rootdisk_mount_prop, "");
+        return;
     }
+
+    // 1. dm-N
+    //  dev.mnt.dev.data = dm-N
+    //  dev.mnt.blk.data = sdaN or mmcblk0pN
+    //  dev.mnt.rootdisk.data = sda or mmcblk0
+    //
+    // 2. sdaN or mmcblk0pN
+    //  dev.mnt.dev.data = sdaN or mmcblk0pN
+    //  dev.mnt.blk.data = sdaN or mmcblk0pN
+    //  dev.mnt.rootdisk.data = sda or mmcblk0
+    android::base::SetProperty(dev_mount_prop, target);
+    android::base::SetProperty(blk_mount_prop, diskpart);
+    android::base::SetProperty(rootdisk_mount_prop, rootdisk);
 }
 
 }  // namespace

rootdir/init.rc

@@ -1085,9 +1085,11 @@ on boot
     mkdir /dev/sys/fs/by-name 0755 system system
     symlink /sys/fs/f2fs/${dev.mnt.dev.data} /dev/sys/fs/by-name/userdata
 
-    # to access dm-<num> sysfs
+    # dev.mnt.dev.data=dm-N, dev.mnt.blk.data=sdaN/mmcblk0pN, dev.mnt.rootdisk.data=sda/mmcblk0, or
+    # dev.mnt.dev.data=sdaN/mmcblk0pN, dev.mnt.blk.data=sdaN/mmcblk0pN, dev.mnt.rootdisk.data=sda/mmcblk0
     mkdir /dev/sys/block/by-name 0755 system system
     symlink /sys/class/block/${dev.mnt.dev.data} /dev/sys/block/by-name/userdata
+    symlink /sys/class/block/${dev.mnt.rootdisk.data} /dev/sys/block/by-name/rootdisk
 
     # F2FS tuning. Set cp_interval larger than dirty_expire_centisecs, 30 secs,
     # to avoid power consumption when system becomes mostly idle. Be careful
@@ -1099,8 +1101,9 @@ on boot
 
     # limit discard size to 128MB in order to avoid long IO latency
     # for filesystem tuning first (dm or sda)
-    # Note that, if dm-<num> is used, sda/mmcblk0 should be tuned in vendor/init.rc
+    # this requires enabling selinux entry for sda/mmcblk0 in vendor side
     write /dev/sys/block/by-name/userdata/queue/discard_max_bytes 134217728
+    write /dev/sys/block/by-name/rootdisk/queue/discard_max_bytes 134217728
 
     # Permissions for System Server and daemons.
     chown system system /sys/power/autosleep