fastboot: Mount /metadata before overlayfs teardown.

fs_mgr_overlayfs needs access to /metadata to tell whether or not the
scratch partition exists on /data.

Bug: 134949511
Test: adb remount, fastboot flash system
Change-Id: I3a09aae495d691e9c1a1e25a8fb3514e355ecd05

fastboot/device/commands.cpp

@@ -31,7 +31,6 @@
 #include <cutils/android_reboot.h>
 #include <ext4_utils/wipe.h>
 #include <fs_mgr.h>
-#include <fs_mgr/roots.h>
 #include <libgsi/libgsi.h>
 #include <liblp/builder.h>
 #include <liblp/liblp.h>
@@ -550,42 +549,6 @@ bool UpdateSuperHandler(FastbootDevice* device, const std::vector<std::string>&
     return UpdateSuper(device, args[1], wipe);
 }
 
-class AutoMountMetadata {
-  public:
-    AutoMountMetadata() {
-        android::fs_mgr::Fstab proc_mounts;
-        if (!ReadFstabFromFile("/proc/mounts", &proc_mounts)) {
-            LOG(ERROR) << "Could not read /proc/mounts";
-            return;
-        }
-
-        auto iter = std::find_if(proc_mounts.begin(), proc_mounts.end(),
-                [](const auto& entry) { return entry.mount_point == "/metadata"; });
-        if (iter != proc_mounts.end()) {
-            mounted_ = true;
-            return;
-        }
-
-        if (!ReadDefaultFstab(&fstab_)) {
-            LOG(ERROR) << "Could not read default fstab";
-            return;
-        }
-        mounted_ = EnsurePathMounted(&fstab_, "/metadata");
-        should_unmount_ = true;
-    }
-    ~AutoMountMetadata() {
-        if (mounted_ && should_unmount_) {
-            EnsurePathUnmounted(&fstab_, "/metadata");
-        }
-    }
-    explicit operator bool() const { return mounted_; }
-
-  private:
-    android::fs_mgr::Fstab fstab_;
-    bool mounted_ = false;
-    bool should_unmount_ = false;
-};
-
 bool GsiHandler(FastbootDevice* device, const std::vector<std::string>& args) {
     if (args.size() != 2) {
         return device->WriteFail("Invalid arguments");

fastboot/device/flashing.cpp

@@ -21,6 +21,7 @@
 
 #include <algorithm>
 #include <memory>
+#include <optional>
 #include <set>
 #include <string>
 
@@ -56,6 +57,7 @@ void WipeOverlayfsForPartition(FastbootDevice* device, const std::string& partit
     Fstab fstab;
     ReadDefaultFstab(&fstab);
 
+    std::optional<AutoMountMetadata> mount_metadata;
     for (const auto& entry : fstab) {
         auto partition = android::base::Basename(entry.mount_point);
         if ("/" == entry.mount_point) {
@@ -63,6 +65,7 @@ void WipeOverlayfsForPartition(FastbootDevice* device, const std::string& partit
         }
 
         if ((partition + device->GetCurrentSlot()) == partition_name) {
+            mount_metadata.emplace();
             fs_mgr_overlayfs_teardown(entry.mount_point.c_str());
         }
     }

fastboot/device/utility.cpp

@@ -26,6 +26,7 @@
 #include <android-base/properties.h>
 #include <android-base/strings.h>
 #include <fs_mgr.h>
+#include <fs_mgr/roots.h>
 #include <fs_mgr_dm_linear.h>
 #include <liblp/builder.h>
 #include <liblp/liblp.h>
@@ -240,3 +241,29 @@ std::string GetSuperSlotSuffix(FastbootDevice* device, const std::string& partit
     }
     return current_slot_suffix;
 }
+
+AutoMountMetadata::AutoMountMetadata() {
+    android::fs_mgr::Fstab proc_mounts;
+    if (!ReadFstabFromFile("/proc/mounts", &proc_mounts)) {
+        LOG(ERROR) << "Could not read /proc/mounts";
+        return;
+    }
+
+    if (GetEntryForMountPoint(&proc_mounts, "/metadata")) {
+        mounted_ = true;
+        return;
+    }
+
+    if (!ReadDefaultFstab(&fstab_)) {
+        LOG(ERROR) << "Could not read default fstab";
+        return;
+    }
+    mounted_ = EnsurePathMounted(&fstab_, "/metadata");
+    should_unmount_ = true;
+}
+
+AutoMountMetadata::~AutoMountMetadata() {
+    if (mounted_ && should_unmount_) {
+        EnsurePathUnmounted(&fstab_, "/metadata");
+    }
+}

fastboot/device/utility.h

@@ -20,6 +20,7 @@
 
 #include <android-base/unique_fd.h>
 #include <android/hardware/boot/1.0/IBootControl.h>
+#include <fstab/fstab.h>
 #include <liblp/liblp.h>
 
 // Logical partitions are only mapped to a block device as needed, and
@@ -51,6 +52,18 @@ class PartitionHandle {
     std::function<void()> closer_;
 };
 
+class AutoMountMetadata {
+  public:
+    AutoMountMetadata();
+    ~AutoMountMetadata();
+    explicit operator bool() const { return mounted_; }
+
+  private:
+    android::fs_mgr::Fstab fstab_;
+    bool mounted_ = false;
+    bool should_unmount_ = false;
+};
+
 class FastbootDevice;
 
 // On normal devices, the super partition is always named "super". On retrofit