From f495fe798b180345371beec82e4aa74c5feb0dea Mon Sep 17 00:00:00 2001
From: Nikita Ioffe <ioffe@google.com>
Date: Fri, 6 Mar 2020 17:36:05 +0000
Subject: [PATCH] fs_mgr_get_mounted_entry_for_userdata: handle logical
 partitions

In case of GSI on DSU, /data is mounted on the following stack:
userdata -> userdata_gsi -> actual block device, and fstab returned from
ReadDefaultFstab() function will say that /data should be
mounted onto userdata_gsi. This configuration wasn't supported.

To support it, fs_mgr_get_mounted_entry_for_userdata now unwinds the
dm-device stack /data is mounted onto, and for each entry in fstab
resolves corresponding block device (in case of logical partitions by
asking DeviceMapper to resolve name -> path, and for other cases by
reading a symlink), and then checking whenever resolved block device
belongs to the unwinded stack.

Test: on both normal boot & DSU
Test: atest CtsUserspaceRebootHostSideTestCases
Test: atest CtsFsMgrTestCases
Bug: 148612148
Change-Id: I1bb3e64ae92d56de905b4f7f1997b7499b101b0f
---
 fs_mgr/fs_mgr.cpp | 78 ++++++++++++++++++-----------------------------
 1 file changed, 30 insertions(+), 48 deletions(-)

diff --git a/fs_mgr/fs_mgr.cpp b/fs_mgr/fs_mgr.cpp
index 2e46b4f87..d509e7153 100644
--- a/fs_mgr/fs_mgr.cpp
+++ b/fs_mgr/fs_mgr.cpp
@@ -1589,76 +1589,58 @@ static bool fs_mgr_unmount_all_data_mounts(const std::string& block_device) {
     }
 }
 
-static std::string ResolveBlockDevice(const std::string& block_device) {
+static bool UnwindDmDeviceStack(const std::string& block_device,
+                                std::vector<std::string>* dm_stack) {
     if (!StartsWith(block_device, "/dev/block/")) {
         LWARNING << block_device << " is not a block device";
-        return block_device;
+        return false;
     }
-    std::string name = block_device.substr(5);
-    if (!StartsWith(name, "block/dm-")) {
-        // Not a dm-device, but might be a symlink. Optimistically try to readlink.
-        std::string result;
-        if (Readlink(block_device, &result)) {
-            return result;
-        } else if (errno == EINVAL) {
-            // After all, it wasn't a symlink.
-            return block_device;
-        } else {
-            LERROR << "Failed to readlink " << block_device;
-            return "";
-        }
-    }
-    // It's a dm-device, let's find what's inside!
-    std::string sys_dir = "/sys/" + name;
+    std::string current = block_device;
+    DeviceMapper& dm = DeviceMapper::Instance();
     while (true) {
-        std::string slaves_dir = sys_dir + "/slaves";
-        std::unique_ptr<DIR, decltype(&closedir)> dir(opendir(slaves_dir.c_str()), closedir);
-        if (!dir) {
-            LERROR << "Failed to open " << slaves_dir;
-            return "";
+        dm_stack->push_back(current);
+        if (!dm.IsDmBlockDevice(current)) {
+            break;
         }
-        std::string sub_device_name = "";
-        for (auto entry = readdir(dir.get()); entry; entry = readdir(dir.get())) {
-            if (entry->d_type != DT_LNK) continue;
-            if (!sub_device_name.empty()) {
-                LERROR << "Too many slaves in " << slaves_dir;
-                return "";
-            }
-            sub_device_name = entry->d_name;
+        auto parent = dm.GetParentBlockDeviceByPath(current);
+        if (!parent) {
+            return false;
         }
-        if (sub_device_name.empty()) {
-            LERROR << "No slaves in " << slaves_dir;
-            return "";
-        }
-        if (!StartsWith(sub_device_name, "dm-")) {
-            // Not a dm-device! We can stop now.
-            return "/dev/block/" + sub_device_name;
-        }
-        // Still a dm-device, keep digging.
-        sys_dir = "/sys/block/" + sub_device_name;
+        current = *parent;
     }
+    return true;
 }
 
 FstabEntry* fs_mgr_get_mounted_entry_for_userdata(Fstab* fstab, const FstabEntry& mounted_entry) {
-    std::string resolved_block_device = ResolveBlockDevice(mounted_entry.blk_device);
-    if (resolved_block_device.empty()) {
+    if (mounted_entry.mount_point != "/data") {
+        LERROR << mounted_entry.mount_point << " is not /data";
+        return nullptr;
+    }
+    std::vector<std::string> dm_stack;
+    if (!UnwindDmDeviceStack(mounted_entry.blk_device, &dm_stack)) {
+        LERROR << "Failed to unwind dm-device stack for " << mounted_entry.blk_device;
         return nullptr;
     }
-    LINFO << "/data is mounted on " << resolved_block_device;
     for (auto& entry : *fstab) {
         if (entry.mount_point != "/data") {
             continue;
         }
         std::string block_device;
-        if (!Readlink(entry.blk_device, &block_device)) {
-            LWARNING << "Failed to readlink " << entry.blk_device;
+        if (entry.fs_mgr_flags.logical) {
+            if (!fs_mgr_update_logical_partition(&entry)) {
+                LERROR << "Failed to update logic partition " << entry.blk_device;
+                continue;
+            }
+            block_device = entry.blk_device;
+        } else if (!Readlink(entry.blk_device, &block_device)) {
+            PWARNING << "Failed to read link " << entry.blk_device;
             block_device = entry.blk_device;
         }
-        if (block_device == resolved_block_device) {
+        if (std::find(dm_stack.begin(), dm_stack.end(), block_device) != dm_stack.end()) {
             return &entry;
         }
     }
-    LERROR << "Didn't find entry that was used to mount /data";
+    LERROR << "Didn't find entry that was used to mount /data onto " << mounted_entry.blk_device;
     return nullptr;
 }