API doc improvement to FileIntegrityManager

     * Enables fs-verity to the owned file under the calling app's private directory. It always uses

     * the common configuration, i.e. SHA-256 digest algorithm, 4K block size, and without salt.

     *

     * The operation can only succeed when the file is not opened as writable by any process.

     * <p>For enabling fs-verity to succeed, the device must support fs-verity, the file must be

     * writable by the app and not already have fs-verity enabled, and the file must not currently

     * be open for writing by any process. To check whether the device supports fs-verity, use

     * {@link #isApkVeritySupported()}.

     *

     * It takes O(file size) time to build the underlying data structure for continuous

     * <p>It takes O(file size) time to build the underlying data structure for continuous

     * verification. The operation is atomic, i.e. it's either enabled or not, even in case of

     * power failure during or after the call.

     *

     * Note for the API users: When the file's authenticity is crucial, the app typical needs to

     * <p>Note for the API users: When the file's authenticity is crucial, the app typical needs to

     * perform a signature check by itself before using the file. The signature is often delivered

     * as a separate file and stored next to the targeting file in the filesystem. The public key of

     * the signer (normally the same app developer) can be put in the APK, and the app can use the

     * public key to verify the signature to the file's actual fs-verity digest (from {@link

     * #getFsVerityDigest}) before using the file. The exact format is not prescribed by the

     * #getFsVerityDigest(File)}) before using the file. The exact format is not prescribed by the

     * framework. App developers may choose to use common practices like JCA for the signing and

     * verification, or their own preferred approach.

     *

     * @param file The file to enable fs-verity. It should be an absolute path.

     * @param file The file to enable fs-verity. It must represent an absolute path.

     * @throws IllegalArgumentException If the provided file is not an absolute path.

     * @throws IOException If the operation failed.

     *

     * @see <a href="https://www.kernel.org/doc/html/next/filesystems/fsverity.html">Kernel doc</a>

     */

    @FlaggedApi(Flags.FLAG_FSVERITY_API)

    public void setupFsVerity(@NonNull File file) throws IOException {

        if (!file.isAbsolute()) {

            // fs-verity is to be enabled by installd, which enforces the validation to the

            // (untrusted) file path passed from here. To make this less error prone, installd

            // accepts only absolute path. When a relative path is provided, we fail with an

            // explicit exception to help developers understand the requirement to use an absolute

            // path.

            throw new IllegalArgumentException("Expect an absolute path");

        }

        IFsveritySetupAuthToken authToken;

    }

    /**

     * Returns the fs-verity digest for the owned file under the calling app's

     * private directory, or null when the file does not have fs-verity enabled.

     * Returns the fs-verity digest for the owned file under the calling app's private directory, or

     * null when the file does not have fs-verity enabled (including when fs-verity is not supported

     * on older devices).

     *

     * @param file The file to measure the fs-verity digest.

     * @return The fs-verity digeset in byte[], null if none.

     * @return The fs-verity digest in byte[], null if none.

     * @see <a href="https://www.kernel.org/doc/html/next/filesystems/fsverity.html">Kernel doc</a>

     */

    @FlaggedApi(Flags.FLAG_FSVERITY_API)