Use exFAT for SDXC cards

When both VFAT and exFAT are supported VFAT will only be used to
format card. Use exFAT for cards larger than 32GB per SDXC standard.

Test: build, manual, mount exFAT volume
Bug: 80202067
Change-Id: If504f9685256a669c5801a69d69d5a214ad27455

model/PublicVolume.cpp

@@ -246,28 +246,53 @@ status_t PublicVolume::doUnmount() {
 }
 
 status_t PublicVolume::doFormat(const std::string& fsType) {
-    if ((fsType == "vfat" || fsType == "auto") && vfat::IsSupported()) {
-        if (WipeBlockDevice(mDevPath) != OK) {
-            LOG(WARNING) << getId() << " failed to wipe";
+    bool useVfat = vfat::IsSupported();
+    bool useExfat = exfat::IsSupported();
+    status_t res = OK;
+
+    // Resolve the target filesystem type
+    if (fsType == "auto" && useVfat && useExfat) {
+        uint64_t size = 0;
+
+        res = GetBlockDevSize(mDevPath, &size);
+        if (res != OK) {
+            LOG(ERROR) << "Couldn't get device size " << mDevPath;
+            return res;
         }
-        if (vfat::Format(mDevPath, 0)) {
-            LOG(ERROR) << getId() << " failed to format";
-            return -errno;
-        }
-    } else if ((fsType == "exfat" || fsType == "auto") && exfat::IsSupported()) {
-        if (WipeBlockDevice(mDevPath) != OK) {
-            LOG(WARNING) << getId() << " failed to wipe";
-        }
-        if (exfat::Format(mDevPath)) {
-            LOG(ERROR) << getId() << " failed to format";
-            return -errno;
+
+        // If both vfat & exfat are supported use exfat for SDXC (>~32GiB) cards
+        if (size > 32896LL * 1024 * 1024) {
+            useVfat = false;
+        } else {
+            useExfat = false;
         }
-    } else {
+    } else if (fsType == "vfat") {
+        useExfat = false;
+    } else if (fsType == "exfat") {
+        useVfat = false;
+    }
+
+    if (!useVfat && !useExfat) {
         LOG(ERROR) << "Unsupported filesystem " << fsType;
         return -EINVAL;
     }
 
-    return OK;
+    if (WipeBlockDevice(mDevPath) != OK) {
+        LOG(WARNING) << getId() << " failed to wipe";
+    }
+
+    if (useVfat) {
+        res = vfat::Format(mDevPath, 0);
+    } else if (useExfat) {
+        res = exfat::Format(mDevPath);
+    }
+
+    if (res != OK) {
+        LOG(ERROR) << getId() << " failed to format";
+        res = -errno;
+    }
+
+    return res;
 }
 
 }  // namespace vold