commit dcf1c1f46235637a6d1057c88e6d1fed88e1b90a
author Yi-Yo Chiang <yochiang@google.com> Wed May 19 16:25:34 2021 +0800
committer Yo Chiang <yochiang@google.com> Thu May 20 06:40:27 2021 +0000
tree 578fa6aceec220f826edb0df2642b1fbdcafc2ea
parent b440fc9c06b6b612a7e5c9ae87b0c3733042f9ff

fs_mgr_overlayfs: Polish fs_mgr_overlayfs_mount_fstab_entry()

* Add logs.
* Append "override_creds=off" overlayfs mount flag only if
  fs_mgr_overlayfs_valid() returns kOverrideCredsRequired.
  Pre-4.6 kernels or kernels without the override_creds patch don't
  need or don't recognize the override_creds mount flag.
  (Background: I832c8ca3fce0269bdef4ce988541adb7ba9662ed)
* mkdir(mount_point) before mount() to ensure the mount point exists.
  This could happen if the mount point is in a tmpfs, such as /mnt.

Bug: 186342252
Test: Boot to normal with overlayfs mount entries in first stage fstab
Change-Id: I1a05696346610d7fd61de6d25c379520fd58ca9b

fs_mgr/fs_mgr_overlayfs.cpp

diff --git a/fs_mgr/fs_mgr_overlayfs.cpp b/fs_mgr/fs_mgr_overlayfs.cpp
index 9a94d79..925d03f 100644
--- a/fs_mgr/fs_mgr_overlayfs.cpp
+++ b/fs_mgr/fs_mgr_overlayfs.cpp
@@ -92,7 +92,7 @@
     return false;
 }
 
-bool fs_mgr_overlayfs_mount_fstab_entry(const std::string&, const std::string&) {
+bool fs_mgr_overlayfs_mount_fstab_entry(const android::fs_mgr::FstabEntry&) {
     return false;
 }
 
@@ -1299,16 +1299,30 @@
     }
 }
 
-bool fs_mgr_overlayfs_mount_fstab_entry(const std::string& lowers,
-                                        const std::string& mount_point) {
+bool fs_mgr_overlayfs_mount_fstab_entry(const android::fs_mgr::FstabEntry& entry) {
     if (fs_mgr_overlayfs_invalid()) return false;
 
-    std::string aux = "lowerdir=" + lowers + ",override_creds=off";
-    auto rc = mount("overlay", mount_point.c_str(), "overlay", MS_RDONLY | MS_NOATIME, aux.c_str());
+    // Create the mount point in case it doesn't exist.
+    mkdir(entry.mount_point.c_str(), 0755);
 
-    if (rc == 0) return true;
+    auto options = kLowerdirOption + entry.lowerdir;
+    if (fs_mgr_overlayfs_valid() == OverlayfsValidResult::kOverrideCredsRequired) {
+        options += ",override_creds=off";
+    }
 
-    return false;
+    // Use .blk_device as the mount() source for debugging purposes.
+    // Overlayfs is pseudo filesystem, so the source device is a symbolic value and isn't used to
+    // back the filesystem. /proc/mounts would show the source as the device name of the mount.
+    auto report = "__mount(source=" + entry.blk_device + ",target=" + entry.mount_point +
+                  ",type=overlay," + options + ")=";
+    auto ret = mount(entry.blk_device.c_str(), entry.mount_point.c_str(), "overlay",
+                     MS_RDONLY | MS_NOATIME, options.c_str());
+    if (ret) {
+        PERROR << report << ret;
+        return false;
+    }
+    LINFO << report << ret;
+    return true;
 }
 
 bool fs_mgr_overlayfs_mount_all(Fstab* fstab) {

fs_mgr/include/fs_mgr_overlayfs.h

diff --git a/fs_mgr/include/fs_mgr_overlayfs.h b/fs_mgr/include/fs_mgr_overlayfs.h
index ac95ef5..22d12e7 100644
--- a/fs_mgr/include/fs_mgr_overlayfs.h
+++ b/fs_mgr/include/fs_mgr_overlayfs.h
@@ -27,7 +27,7 @@
 android::fs_mgr::Fstab fs_mgr_overlayfs_candidate_list(const android::fs_mgr::Fstab& fstab);
 
 bool fs_mgr_overlayfs_mount_all(android::fs_mgr::Fstab* fstab);
-bool fs_mgr_overlayfs_mount_fstab_entry (const std::string& lowers, const std::string& mount_point);
+bool fs_mgr_overlayfs_mount_fstab_entry(const android::fs_mgr::FstabEntry& entry);
 std::vector<std::string> fs_mgr_overlayfs_required_devices(android::fs_mgr::Fstab* fstab);
 bool fs_mgr_overlayfs_setup(const char* backing = nullptr, const char* mount_point = nullptr,
                             bool* change = nullptr, bool force = true);

init/first_stage_mount.cpp

diff --git a/init/first_stage_mount.cpp b/init/first_stage_mount.cpp
index 87e23ab..616d285 100644
--- a/init/first_stage_mount.cpp
+++ b/init/first_stage_mount.cpp
@@ -542,6 +542,7 @@
             continue;
         }
 
+        // Handle overlayfs entries later.
         if (current->fs_type == "overlay") {
             ++current;
             continue;
@@ -571,6 +572,12 @@
         current = end;
     }
 
+    for (const auto& entry : fstab_) {
+        if (entry.fs_type == "overlay") {
+            fs_mgr_overlayfs_mount_fstab_entry(entry);
+        }
+    }
+
     // If we don't see /system or / in the fstab, then we need to create an root entry for
     // overlayfs.
     if (!GetEntryForMountPoint(&fstab_, "/system") && !GetEntryForMountPoint(&fstab_, "/")) {
@@ -596,13 +603,6 @@
     };
     MapScratchPartitionIfNeeded(&fstab_, init_devices);
 
-    for (auto current = fstab_.begin(); current != fstab_.end(); ) {
-        if (current->fs_type == "overlay") {
-            fs_mgr_overlayfs_mount_fstab_entry(current->lowerdir, current->mount_point);
-        }
-        ++current;
-    }
-
     fs_mgr_overlayfs_mount_all(&fstab_);
 
     return true;