recovery: make /etc/fstab only include entries that match the detected fs type

* toybox's `mount` does not support multiple entries like we do,
   so if we can detect the filesystem of an fstab enrtry print that
   and only that one to /etc/fstab, so that mounting via toybox has
   a better chance of succeding.

 * as a bonus, this patch also gets rid of duplicates in /etc/fstab
   caused by the fact that ReadDefaultFstab() combines entries from
   DT and from recovery.fstab

Change-Id: Iec4ab38044054555d2a33da6f5d53de7716e7bee

recovery_utils/Android.bp

@@ -48,6 +48,10 @@ cc_defaults {
         "libhealthhalutils",
         "libhealthshim",
     ],
+
+    whole_static_libs: [
+        "libext2_blkid",
+    ],
 }
 
 // A utility lib that's local to recovery (in contrast, libotautil is exposed to device-specific

recovery_utils/roots.cpp

@@ -34,6 +34,7 @@
 #include <android-base/properties.h>
 #include <android-base/stringprintf.h>
 #include <android-base/unique_fd.h>
+#include <blkid/blkid.h>
 #include <ext4_utils/ext4_utils.h>
 #include <ext4_utils/wipe.h>
 #include <fs_mgr.h>
@@ -59,18 +60,31 @@ static Fstab fstab;
 
 constexpr const char* CACHE_ROOT = "/cache";
 
+FstabEntry* fstab_entry_for_mount_point_detect_fs(const std::string& path) {
+  FstabEntry* found = android::fs_mgr::GetEntryForMountPoint(&fstab, path);
+  if (found == nullptr) {
+    return nullptr;
+  }
+
+  if (char* detected_fs_type = blkid_get_tag_value(nullptr, "TYPE", found->blk_device.c_str())) {
+    for (auto& entry : fstab) {
+      if (entry.mount_point == path && entry.fs_type == detected_fs_type) {
+        found = &entry;
+        break;
+      }
+    }
+    free(detected_fs_type);
+  }
+
+  return found;
+}
+
 void load_volume_table() {
   if (!ReadDefaultFstab(&fstab)) {
     LOG(ERROR) << "Failed to read default fstab";
     return;
   }
 
-  // Create a boring /etc/fstab so tools like Busybox work
-  FILE* file = fopen("/etc/fstab", "w");
-  if (!file) {
-    LOG(ERROR) << "Unable to create /etc/fstab";
-  }
-
   fstab.emplace_back(FstabEntry{
       .blk_device = "ramdisk",
       .mount_point = "/tmp",
@@ -78,20 +92,34 @@ void load_volume_table() {
       .length = 0,
   });
 
+  Fstab fake_fstab;
   std::cout << "recovery filesystem table" << std::endl << "=========================" << std::endl;
   for (size_t i = 0; i < fstab.size(); ++i) {
     const auto& entry = fstab[i];
     std::cout << "  " << i << " " << entry.mount_point << " "
               << " " << entry.fs_type << " " << entry.blk_device << " " << entry.length
               << std::endl;
-    if (file) {
-      write_fstab_entry(entry, file);
+
+    if (std::find_if(fake_fstab.begin(), fake_fstab.end(), [entry](const FstabEntry& e) {
+          return entry.mount_point == e.mount_point;
+        }) == fake_fstab.end()) {
+      FstabEntry* entry_detectfs = fstab_entry_for_mount_point_detect_fs(entry.mount_point);
+      if (entry_detectfs == &entry) {
+        fake_fstab.emplace_back(entry);
+      }
     }
   }
   std::cout << std::endl;
 
+  // Create a boring /etc/fstab so tools like Busybox work
+  FILE* file = fopen("/etc/fstab", "w");
   if (file) {
+    for (auto& entry : fake_fstab) {
+      write_fstab_entry(entry, file);
+    }
     fclose(file);
+  } else {
+    LOG(ERROR) << "Unable to create /etc/fstab";
   }
 }