From 251ec05f017fb81628dd1995fb587913063702e4 Mon Sep 17 00:00:00 2001
From: David Anderson <dvander@google.com>
Date: Tue, 20 Aug 2019 16:31:46 -0700
Subject: [PATCH] liblp: Support sdcards in PartitionOpener.

Before ImageManager was introduced, gsid avoided using PartitionOpener
when writing to external media. PartitionOpener couldn't interact with
non-boot devices, because it prepends /dev/block/by-name. We hacked
around this in both gsid and in first-stage init, which manually detects
the problem and prepends /dev/block instead.

After the ImageManager refactoring, sdcard support broke in gsid,
because it started relying on PartitionOpener. Let's fix this by allowing
/dev/block for mmcblk* names in PartitionOpener.

Bug: 139204329
Test: fiemap_image_test gtest
Change-Id: Ic1cbdbe0a18fc09522ee38cc62b35fd8193ce250
---
 fs_mgr/liblp/partition_opener.cpp | 16 +++++++++++++++-
 init/first_stage_mount.cpp        | 16 ++++------------
 2 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/fs_mgr/liblp/partition_opener.cpp b/fs_mgr/liblp/partition_opener.cpp
index f1e8fc20c..1d4db8525 100644
--- a/fs_mgr/liblp/partition_opener.cpp
+++ b/fs_mgr/liblp/partition_opener.cpp
@@ -41,7 +41,21 @@ std::string GetPartitionAbsolutePath(const std::string& path) {
     if (android::base::StartsWith(path, "/")) {
         return path;
     }
-    return "/dev/block/by-name/" + path;
+
+    auto by_name = "/dev/block/by-name/" + path;
+    if (access(by_name.c_str(), F_OK) != 0) {
+        // If the by-name symlink doesn't exist, as a special case we allow
+        // certain devices to be used as partition names. This can happen if a
+        // Dynamic System Update is installed to an sdcard, which won't be in
+        // the boot device list.
+        //
+        // We whitelist because most devices in /dev/block are not valid for
+        // storing fiemaps.
+        if (android::base::StartsWith(path, "mmcblk")) {
+            return "/dev/block/" + path;
+        }
+    }
+    return by_name;
 }
 
 bool GetBlockDeviceInfo(const std::string& block_device, BlockDeviceInfo* device_info) {
diff --git a/init/first_stage_mount.cpp b/init/first_stage_mount.cpp
index 1a5ed2847..dffd6af00 100644
--- a/init/first_stage_mount.cpp
+++ b/init/first_stage_mount.cpp
@@ -602,19 +602,11 @@ void FirstStageMount::UseGsiIfPresent() {
         return;
     }
 
-    // Find the name of the super partition for the GSI. It will either be
-    // "userdata", or a block device such as an sdcard. There are no by-name
-    // partitions other than userdata that we support installing GSIs to.
+    // Find the super name. PartitionOpener will ensure this translates to the
+    // correct block device path.
     auto super = GetMetadataSuperBlockDevice(*metadata.get());
-    std::string super_name = android::fs_mgr::GetBlockDevicePartitionName(*super);
-    std::string super_path;
-    if (super_name == "userdata") {
-        super_path = "/dev/block/by-name/" + super_name;
-    } else {
-        super_path = "/dev/block/" + super_name;
-    }
-
-    if (!android::fs_mgr::CreateLogicalPartitions(*metadata.get(), super_path)) {
+    auto super_name = android::fs_mgr::GetBlockDevicePartitionName(*super);
+    if (!android::fs_mgr::CreateLogicalPartitions(*metadata.get(), super_name)) {
         LOG(ERROR) << "GSI partition layout could not be instantiated";
         return;
     }