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[mediawiki.git] / includes / filebackend / FileBackendMultiWrite.php

<?php
/**
 * Proxy backend that mirrors writes to several internal backends.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 * @ingroup FileBackend
 * @author Aaron Schulz
 */

/**
 * @brief Proxy backend that mirrors writes to several internal backends.
 *
 * This class defines a multi-write backend. Multiple backends can be
 * registered to this proxy backend and it will act as a single backend.
 * Use this when all access to those backends is through this proxy backend.
 * At least one of the backends must be declared the "master" backend.
 *
 * Only use this class when transitioning from one storage system to another.
 *
 * Read operations are only done on the 'master' backend for consistency.
 * Write operations are performed on all backends, starting with the master.
 * This makes a best-effort to have transactional semantics, but since requests
 * may sometimes fail, the use of "autoResync" or background scripts to fix
 * inconsistencies is important.
 *
 * @ingroup FileBackend
 * @since 1.19
 */
class FileBackendMultiWrite extends FileBackend {
        /** @var FileBackendStore[] Prioritized list of FileBackendStore objects */
        protected $backends = array();

        /** @var int Index of master backend */
        protected $masterIndex = -1;
        /** @var int Index of read affinity backend */
        protected $readIndex = -1;

        /** @var int Bitfield */
        protected $syncChecks = 0;
        /** @var string|bool */
        protected $autoResync = false;

        /** @var bool */
        protected $asyncWrites = false;

        /* Possible internal backend consistency checks */
        const CHECK_SIZE = 1;
        const CHECK_TIME = 2;
        const CHECK_SHA1 = 4;

        /**
         * Construct a proxy backend that consists of several internal backends.
         * Locking, journaling, and read-only checks are handled by the proxy backend.
         *
         * Additional $config params include:
         *   - backends       : Array of backend config and multi-backend settings.
         *                      Each value is the config used in the constructor of a
         *                      FileBackendStore class, but with these additional settings:
         *                        - class         : The name of the backend class
         *                        - isMultiMaster : This must be set for one backend.
         *                        - readAffinity  : Use this for reads without 'latest' set.
         *                        - template:     : If given a backend name, this will use
         *                                          the config of that backend as a template.
         *                                          Values specified here take precedence.
         *   - syncChecks     : Integer bitfield of internal backend sync checks to perform.
         *                      Possible bits include the FileBackendMultiWrite::CHECK_* constants.
         *                      There are constants for SIZE, TIME, and SHA1.
         *                      The checks are done before allowing any file operations.
         *   - autoResync     : Automatically resync the clone backends to the master backend
         *                      when pre-operation sync checks fail. This should only be used
         *                      if the master backend is stable and not missing any files.
         *                      Use "conservative" to limit resyncing to copying newer master
         *                      backend files over older (or non-existing) clone backend files.
         *                      Cases that cannot be handled will result in operation abortion.
         *   - replication    : Set to 'async' to defer file operations on the non-master backends.
         *                      This will apply such updates post-send for web requests. Note that
         *                      any checks from "syncChecks" are still synchronous.
         *
         * @param array $config
         * @throws FileBackendError
         */
        public function __construct( array $config ) {
                parent::__construct( $config );
                $this->syncChecks = isset( $config['syncChecks'] )
                        ? $config['syncChecks']
                        : self::CHECK_SIZE;
                $this->autoResync = isset( $config['autoResync'] )
                        ? $config['autoResync']
                        : false;
                $this->asyncWrites = isset( $config['replication'] ) && $config['replication'] === 'async';
                // Construct backends here rather than via registration
                // to keep these backends hidden from outside the proxy.
                $namesUsed = array();
                foreach ( $config['backends'] as $index => $config ) {
                        if ( isset( $config['template'] ) ) {
                                // Config is just a modified version of a registered backend's.
                                // This should only be used when that config is used only by this backend.
                                $config = $config + FileBackendGroup::singleton()->config( $config['template'] );
                        }
                        $name = $config['name'];
                        if ( isset( $namesUsed[$name] ) ) { // don't break FileOp predicates
                                throw new FileBackendError( "Two or more backends defined with the name $name." );
                        }
                        $namesUsed[$name] = 1;
                        // Alter certain sub-backend settings for sanity
                        unset( $config['readOnly'] ); // use proxy backend setting
                        unset( $config['fileJournal'] ); // use proxy backend journal
                        unset( $config['lockManager'] ); // lock under proxy backend
                        $config['wikiId'] = $this->wikiId; // use the proxy backend wiki ID
                        if ( !empty( $config['isMultiMaster'] ) ) {
                                if ( $this->masterIndex >= 0 ) {
                                        throw new FileBackendError( 'More than one master backend defined.' );
                                }
                                $this->masterIndex = $index; // this is the "master"
                                $config['fileJournal'] = $this->fileJournal; // log under proxy backend
                        }
                        if ( !empty( $config['readAffinity'] ) ) {
                                $this->readIndex = $index; // prefer this for reads
                        }
                        // Create sub-backend object
                        if ( !isset( $config['class'] ) ) {
                                throw new FileBackendError( 'No class given for a backend config.' );
                        }
                        $class = $config['class'];
                        $this->backends[$index] = new $class( $config );
                }
                if ( $this->masterIndex < 0 ) { // need backends and must have a master
                        throw new FileBackendError( 'No master backend defined.' );
                }
                if ( $this->readIndex < 0 ) {
                        $this->readIndex = $this->masterIndex; // default
                }
        }

        final protected function doOperationsInternal( array $ops, array $opts ) {
                $status = Status::newGood();

                $mbe = $this->backends[$this->masterIndex]; // convenience

                // Try to lock those files for the scope of this function...
                $scopeLock = null;
                if ( empty( $opts['nonLocking'] ) ) {
                        // Try to lock those files for the scope of this function...
                        /** @noinspection PhpUnusedLocalVariableInspection */
                        $scopeLock = $this->getScopedLocksForOps( $ops, $status );
                        if ( !$status->isOK() ) {
                                return $status; // abort
                        }
                }
                // Clear any cache entries (after locks acquired)
                $this->clearCache();
                $opts['preserveCache'] = true; // only locked files are cached
                // Get the list of paths to read/write...
                $relevantPaths = $this->fileStoragePathsForOps( $ops );
                // Check if the paths are valid and accessible on all backends...
                $status->merge( $this->accessibilityCheck( $relevantPaths ) );
                if ( !$status->isOK() ) {
                        return $status; // abort
                }
                // Do a consistency check to see if the backends are consistent...
                $syncStatus = $this->consistencyCheck( $relevantPaths );
                if ( !$syncStatus->isOK() ) {
                        wfDebugLog( 'FileOperation', get_class( $this ) .
                                " failed sync check: " . FormatJson::encode( $relevantPaths ) );
                        // Try to resync the clone backends to the master on the spot...
                        if ( !$this->autoResync || !$this->resyncFiles( $relevantPaths )->isOK() ) {
                                $status->merge( $syncStatus );

                                return $status; // abort
                        }
                }
                // Actually attempt the operation batch on the master backend...
                $realOps = $this->substOpBatchPaths( $ops, $mbe );
                $masterStatus = $mbe->doOperations( $realOps, $opts );
                $status->merge( $masterStatus );
                // Propagate the operations to the clone backends if there were no unexpected errors
                // and if there were either no expected errors or if the 'force' option was used.
                // However, if nothing succeeded at all, then don't replicate any of the operations.
                // If $ops only had one operation, this might avoid backend sync inconsistencies.
                if ( $masterStatus->isOK() && $masterStatus->successCount > 0 ) {
                        foreach ( $this->backends as $index => $backend ) {
                                if ( $index === $this->masterIndex ) {
                                        continue; // done already
                                }

                                $realOps = $this->substOpBatchPaths( $ops, $backend );
                                if ( $this->asyncWrites ) {
                                        // Bind $scopeLock to the callback to preserve locks
                                        DeferredUpdates::addCallableUpdate(
                                                function() use ( $backend, $realOps, $opts, $scopeLock ) {
                                                        $backend->doOperations( $realOps, $opts );
                                                }
                                        );
                                } else {
                                        $status->merge( $backend->doOperations( $realOps, $opts ) );
                                }
                        }
                }
                // Make 'success', 'successCount', and 'failCount' fields reflect
                // the overall operation, rather than all the batches for each backend.
                // Do this by only using success values from the master backend's batch.
                $status->success = $masterStatus->success;
                $status->successCount = $masterStatus->successCount;
                $status->failCount = $masterStatus->failCount;

                return $status;
        }

        /**
         * Check that a set of files are consistent across all internal backends
         *
         * @param array $paths List of storage paths
         * @return Status
         */
        public function consistencyCheck( array $paths ) {
                $status = Status::newGood();
                if ( $this->syncChecks == 0 || count( $this->backends ) <= 1 ) {
                        return $status; // skip checks
                }

                $mBackend = $this->backends[$this->masterIndex];
                foreach ( $paths as $path ) {
                        $params = array( 'src' => $path, 'latest' => true );
                        $mParams = $this->substOpPaths( $params, $mBackend );
                        // Stat the file on the 'master' backend
                        $mStat = $mBackend->getFileStat( $mParams );
                        if ( $this->syncChecks & self::CHECK_SHA1 ) {
                                $mSha1 = $mBackend->getFileSha1Base36( $mParams );
                        } else {
                                $mSha1 = false;
                        }
                        // Check if all clone backends agree with the master...
                        foreach ( $this->backends as $index => $cBackend ) {
                                if ( $index === $this->masterIndex ) {
                                        continue; // master
                                }
                                $cParams = $this->substOpPaths( $params, $cBackend );
                                $cStat = $cBackend->getFileStat( $cParams );
                                if ( $mStat ) { // file is in master
                                        if ( !$cStat ) { // file should exist
                                                $status->fatal( 'backend-fail-synced', $path );
                                                continue;
                                        }
                                        if ( $this->syncChecks & self::CHECK_SIZE ) {
                                                if ( $cStat['size'] != $mStat['size'] ) { // wrong size
                                                        $status->fatal( 'backend-fail-synced', $path );
                                                        continue;
                                                }
                                        }
                                        if ( $this->syncChecks & self::CHECK_TIME ) {
                                                $mTs = wfTimestamp( TS_UNIX, $mStat['mtime'] );
                                                $cTs = wfTimestamp( TS_UNIX, $cStat['mtime'] );
                                                if ( abs( $mTs - $cTs ) > 30 ) { // outdated file somewhere
                                                        $status->fatal( 'backend-fail-synced', $path );
                                                        continue;
                                                }
                                        }
                                        if ( $this->syncChecks & self::CHECK_SHA1 ) {
                                                if ( $cBackend->getFileSha1Base36( $cParams ) !== $mSha1 ) { // wrong SHA1
                                                        $status->fatal( 'backend-fail-synced', $path );
                                                        continue;
                                                }
                                        }
                                } else { // file is not in master
                                        if ( $cStat ) { // file should not exist
                                                $status->fatal( 'backend-fail-synced', $path );
                                        }
                                }
                        }
                }

                return $status;
        }

        /**
         * Check that a set of file paths are usable across all internal backends
         *
         * @param array $paths List of storage paths
         * @return Status
         */
        public function accessibilityCheck( array $paths ) {
                $status = Status::newGood();
                if ( count( $this->backends ) <= 1 ) {
                        return $status; // skip checks
                }

                foreach ( $paths as $path ) {
                        foreach ( $this->backends as $backend ) {
                                $realPath = $this->substPaths( $path, $backend );
                                if ( !$backend->isPathUsableInternal( $realPath ) ) {
                                        $status->fatal( 'backend-fail-usable', $path );
                                }
                        }
                }

                return $status;
        }

        /**
         * Check that a set of files are consistent across all internal backends
         * and re-synchronize those files against the "multi master" if needed.
         *
         * @param array $paths List of storage paths
         * @return Status
         */
        public function resyncFiles( array $paths ) {
                $status = Status::newGood();

                $mBackend = $this->backends[$this->masterIndex];
                foreach ( $paths as $path ) {
                        $mPath = $this->substPaths( $path, $mBackend );
                        $mSha1 = $mBackend->getFileSha1Base36( array( 'src' => $mPath, 'latest' => true ) );
                        $mStat = $mBackend->getFileStat( array( 'src' => $mPath, 'latest' => true ) );
                        if ( $mStat === null || ( $mSha1 !== false && !$mStat ) ) { // sanity
                                $status->fatal( 'backend-fail-internal', $this->name );
                                wfDebugLog( 'FileOperation', __METHOD__
                                        . ': File is not available on the master backend' );
                                continue; // file is not available on the master backend...
                        }
                        // Check of all clone backends agree with the master...
                        foreach ( $this->backends as $index => $cBackend ) {
                                if ( $index === $this->masterIndex ) {
                                        continue; // master
                                }
                                $cPath = $this->substPaths( $path, $cBackend );
                                $cSha1 = $cBackend->getFileSha1Base36( array( 'src' => $cPath, 'latest' => true ) );
                                $cStat = $cBackend->getFileStat( array( 'src' => $cPath, 'latest' => true ) );
                                if ( $cStat === null || ( $cSha1 !== false && !$cStat ) ) { // sanity
                                        $status->fatal( 'backend-fail-internal', $cBackend->getName() );
                                        wfDebugLog( 'FileOperation', __METHOD__ .
                                                ': File is not available on the clone backend' );
                                        continue; // file is not available on the clone backend...
                                }
                                if ( $mSha1 === $cSha1 ) {
                                        // already synced; nothing to do
                                } elseif ( $mSha1 !== false ) { // file is in master
                                        if ( $this->autoResync === 'conservative'
                                                && $cStat && $cStat['mtime'] > $mStat['mtime']
                                        ) {
                                                $status->fatal( 'backend-fail-synced', $path );
                                                continue; // don't rollback data
                                        }
                                        $fsFile = $mBackend->getLocalReference(
                                                array( 'src' => $mPath, 'latest' => true ) );
                                        $status->merge( $cBackend->quickStore(
                                                array( 'src' => $fsFile->getPath(), 'dst' => $cPath )
                                        ) );
                                } elseif ( $mStat === false ) { // file is not in master
                                        if ( $this->autoResync === 'conservative' ) {
                                                $status->fatal( 'backend-fail-synced', $path );
                                                continue; // don't delete data
                                        }
                                        $status->merge( $cBackend->quickDelete( array( 'src' => $cPath ) ) );
                                }
                        }
                }

                return $status;
        }

        /**
         * Get a list of file storage paths to read or write for a list of operations
         *
         * @param array $ops Same format as doOperations()
         * @return array List of storage paths to files (does not include directories)
         */
        protected function fileStoragePathsForOps( array $ops ) {
                $paths = array();
                foreach ( $ops as $op ) {
                        if ( isset( $op['src'] ) ) {
                                // For things like copy/move/delete with "ignoreMissingSource" and there
                                // is no source file, nothing should happen and there should be no errors.
                                if ( empty( $op['ignoreMissingSource'] )
                                        || $this->fileExists( array( 'src' => $op['src'] ) )
                                ) {
                                        $paths[] = $op['src'];
                                }
                        }
                        if ( isset( $op['srcs'] ) ) {
                                $paths = array_merge( $paths, $op['srcs'] );
                        }
                        if ( isset( $op['dst'] ) ) {
                                $paths[] = $op['dst'];
                        }
                }

                return array_values( array_unique( array_filter( $paths, 'FileBackend::isStoragePath' ) ) );
        }

        /**
         * Substitute the backend name in storage path parameters
         * for a set of operations with that of a given internal backend.
         *
         * @param array $ops List of file operation arrays
         * @param FileBackendStore $backend
         * @return array
         */
        protected function substOpBatchPaths( array $ops, FileBackendStore $backend ) {
                $newOps = array(); // operations
                foreach ( $ops as $op ) {
                        $newOp = $op; // operation
                        foreach ( array( 'src', 'srcs', 'dst', 'dir' ) as $par ) {
                                if ( isset( $newOp[$par] ) ) { // string or array
                                        $newOp[$par] = $this->substPaths( $newOp[$par], $backend );
                                }
                        }
                        $newOps[] = $newOp;
                }

                return $newOps;
        }

        /**
         * Same as substOpBatchPaths() but for a single operation
         *
         * @param array $ops File operation array
         * @param FileBackendStore $backend
         * @return array
         */
        protected function substOpPaths( array $ops, FileBackendStore $backend ) {
                $newOps = $this->substOpBatchPaths( array( $ops ), $backend );

                return $newOps[0];
        }

        /**
         * Substitute the backend of storage paths with an internal backend's name
         *
         * @param array|string $paths List of paths or single string path
         * @param FileBackendStore $backend
         * @return array|string
         */
        protected function substPaths( $paths, FileBackendStore $backend ) {
                return preg_replace(
                        '!^mwstore://' . preg_quote( $this->name, '!' ) . '/!',
                        StringUtils::escapeRegexReplacement( "mwstore://{$backend->getName()}/" ),
                        $paths // string or array
                );
        }

        /**
         * Substitute the backend of internal storage paths with the proxy backend's name
         *
         * @param array|string $paths List of paths or single string path
         * @return array|string
         */
        protected function unsubstPaths( $paths ) {
                return preg_replace(
                        '!^mwstore://([^/]+)!',
                        StringUtils::escapeRegexReplacement( "mwstore://{$this->name}" ),
                        $paths // string or array
                );
        }

        protected function doQuickOperationsInternal( array $ops ) {
                $status = Status::newGood();
                // Do the operations on the master backend; setting Status fields...
                $realOps = $this->substOpBatchPaths( $ops, $this->backends[$this->masterIndex] );
                $masterStatus = $this->backends[$this->masterIndex]->doQuickOperations( $realOps );
                $status->merge( $masterStatus );
                // Propagate the operations to the clone backends...
                foreach ( $this->backends as $index => $backend ) {
                        if ( $index === $this->masterIndex ) {
                                continue; // done already
                        }

                        $realOps = $this->substOpBatchPaths( $ops, $backend );
                        if ( $this->asyncWrites ) {
                                DeferredUpdates::addCallableUpdate(
                                        function() use ( $backend, $realOps ) {
                                                $backend->doQuickOperations( $realOps );
                                        }
                                );
                        } else {
                                $status->merge( $backend->doQuickOperations( $realOps ) );
                        }
                }
                // Make 'success', 'successCount', and 'failCount' fields reflect
                // the overall operation, rather than all the batches for each backend.
                // Do this by only using success values from the master backend's batch.
                $status->success = $masterStatus->success;
                $status->successCount = $masterStatus->successCount;
                $status->failCount = $masterStatus->failCount;

                return $status;
        }

        protected function doPrepare( array $params ) {
                return $this->doDirectoryOp( 'prepare', $params );
        }

        protected function doSecure( array $params ) {
                return $this->doDirectoryOp( 'secure', $params );
        }

        protected function doPublish( array $params ) {
                return $this->doDirectoryOp( 'publish', $params );
        }

        protected function doClean( array $params ) {
                return $this->doDirectoryOp( 'clean', $params );
        }

        /**
         * @param string $method One of (doPrepare,doSecure,doPublish,doClean)
         * @param array $params Method arguments
         * @return Status
         */
        protected function doDirectoryOp( $method, array $params ) {
                $status = Status::newGood();

                $realParams = $this->substOpPaths( $params, $this->backends[$this->masterIndex] );
                $masterStatus = $this->backends[$this->masterIndex]->$method( $realParams );
                $status->merge( $masterStatus );

                foreach ( $this->backends as $index => $backend ) {
                        if ( $index === $this->masterIndex ) {
                                continue; // already done
                        }

                        $realParams = $this->substOpPaths( $params, $backend );
                        if ( $this->asyncWrites ) {
                                DeferredUpdates::addCallableUpdate(
                                        function() use ( $backend, $method, $realParams ) {
                                                $backend->$method( $realParams );
                                        }
                                );
                        } else {
                                $status->merge( $backend->$method( $realParams ) );
                        }
                }

                return $status;
        }

        public function concatenate( array $params ) {
                // We are writing to an FS file, so we don't need to do this per-backend
                $index = $this->getReadIndexFromParams( $params );
                $realParams = $this->substOpPaths( $params, $this->backends[$index] );

                return $this->backends[$index]->concatenate( $realParams );
        }

        public function fileExists( array $params ) {
                $index = $this->getReadIndexFromParams( $params );
                $realParams = $this->substOpPaths( $params, $this->backends[$index] );

                return $this->backends[$index]->fileExists( $realParams );
        }

        public function getFileTimestamp( array $params ) {
                $index = $this->getReadIndexFromParams( $params );
                $realParams = $this->substOpPaths( $params, $this->backends[$index] );

                return $this->backends[$index]->getFileTimestamp( $realParams );
        }

        public function getFileSize( array $params ) {
                $index = $this->getReadIndexFromParams( $params );
                $realParams = $this->substOpPaths( $params, $this->backends[$index] );

                return $this->backends[$index]->getFileSize( $realParams );
        }

        public function getFileStat( array $params ) {
                $index = $this->getReadIndexFromParams( $params );
                $realParams = $this->substOpPaths( $params, $this->backends[$index] );

                return $this->backends[$index]->getFileStat( $realParams );
        }

        public function getFileXAttributes( array $params ) {
                $index = $this->getReadIndexFromParams( $params );
                $realParams = $this->substOpPaths( $params, $this->backends[$index] );

                return $this->backends[$index]->getFileXAttributes( $realParams );
        }

        public function getFileContentsMulti( array $params ) {
                $index = $this->getReadIndexFromParams( $params );
                $realParams = $this->substOpPaths( $params, $this->backends[$index] );

                $contentsM = $this->backends[$index]->getFileContentsMulti( $realParams );

                $contents = array(); // (path => FSFile) mapping using the proxy backend's name
                foreach ( $contentsM as $path => $data ) {
                        $contents[$this->unsubstPaths( $path )] = $data;
                }

                return $contents;
        }

        public function getFileSha1Base36( array $params ) {
                $index = $this->getReadIndexFromParams( $params );
                $realParams = $this->substOpPaths( $params, $this->backends[$index] );

                return $this->backends[$index]->getFileSha1Base36( $realParams );
        }

        public function getFileProps( array $params ) {
                $index = $this->getReadIndexFromParams( $params );
                $realParams = $this->substOpPaths( $params, $this->backends[$index] );

                return $this->backends[$index]->getFileProps( $realParams );
        }

        public function streamFile( array $params ) {
                $index = $this->getReadIndexFromParams( $params );
                $realParams = $this->substOpPaths( $params, $this->backends[$index] );

                return $this->backends[$index]->streamFile( $realParams );
        }

        public function getLocalReferenceMulti( array $params ) {
                $index = $this->getReadIndexFromParams( $params );
                $realParams = $this->substOpPaths( $params, $this->backends[$index] );

                $fsFilesM = $this->backends[$index]->getLocalReferenceMulti( $realParams );

                $fsFiles = array(); // (path => FSFile) mapping using the proxy backend's name
                foreach ( $fsFilesM as $path => $fsFile ) {
                        $fsFiles[$this->unsubstPaths( $path )] = $fsFile;
                }

                return $fsFiles;
        }

        public function getLocalCopyMulti( array $params ) {
                $index = $this->getReadIndexFromParams( $params );
                $realParams = $this->substOpPaths( $params, $this->backends[$index] );

                $tempFilesM = $this->backends[$index]->getLocalCopyMulti( $realParams );

                $tempFiles = array(); // (path => TempFSFile) mapping using the proxy backend's name
                foreach ( $tempFilesM as $path => $tempFile ) {
                        $tempFiles[$this->unsubstPaths( $path )] = $tempFile;
                }

                return $tempFiles;
        }

        public function getFileHttpUrl( array $params ) {
                $index = $this->getReadIndexFromParams( $params );
                $realParams = $this->substOpPaths( $params, $this->backends[$index] );

                return $this->backends[$index]->getFileHttpUrl( $realParams );
        }

        public function directoryExists( array $params ) {
                $realParams = $this->substOpPaths( $params, $this->backends[$this->masterIndex] );

                return $this->backends[$this->masterIndex]->directoryExists( $realParams );
        }

        public function getDirectoryList( array $params ) {
                $realParams = $this->substOpPaths( $params, $this->backends[$this->masterIndex] );

                return $this->backends[$this->masterIndex]->getDirectoryList( $realParams );
        }

        public function getFileList( array $params ) {
                $realParams = $this->substOpPaths( $params, $this->backends[$this->masterIndex] );

                return $this->backends[$this->masterIndex]->getFileList( $realParams );
        }

        public function getFeatures() {
                return $this->backends[$this->masterIndex]->getFeatures();
        }

        public function clearCache( array $paths = null ) {
                foreach ( $this->backends as $backend ) {
                        $realPaths = is_array( $paths ) ? $this->substPaths( $paths, $backend ) : null;
                        $backend->clearCache( $realPaths );
                }
        }

        public function preloadCache( array $paths ) {
                $realPaths = $this->substPaths( $paths, $this->backends[$this->readIndex] );
                $this->backends[$this->readIndex]->preloadCache( $realPaths );
        }

        public function preloadFileStat( array $params ) {
                $index = $this->getReadIndexFromParams( $params );
                $realParams = $this->substOpPaths( $params, $this->backends[$index] );

                return $this->backends[$index]->preloadFileStat( $realParams );
        }

        public function getScopedLocksForOps( array $ops, Status $status ) {
                $realOps = $this->substOpBatchPaths( $ops, $this->backends[$this->masterIndex] );
                $fileOps = $this->backends[$this->masterIndex]->getOperationsInternal( $realOps );
                // Get the paths to lock from the master backend
                $paths = $this->backends[$this->masterIndex]->getPathsToLockForOpsInternal( $fileOps );
                // Get the paths under the proxy backend's name
                $pbPaths = array(
                        LockManager::LOCK_UW => $this->unsubstPaths( $paths[LockManager::LOCK_UW] ),
                        LockManager::LOCK_EX => $this->unsubstPaths( $paths[LockManager::LOCK_EX] )
                );

                // Actually acquire the locks
                return $this->getScopedFileLocks( $pbPaths, 'mixed', $status );
        }

        /**
         * @param array $params
         * @return int The master or read affinity backend index, based on $params['latest']
         */
        protected function getReadIndexFromParams( array $params ) {
                return !empty( $params['latest'] ) ? $this->masterIndex : $this->readIndex;
        }
}