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This change introduces dynamic manifest updates to asset streaming. Asset streaming describes the directory to be streamed in a manifest, which is a proto definition of all content metadata. This information is sufficient to answer `stat` and `readdir` calls in the FUSE layer without additional round-trips to the workstation. When a directory is streamed for the first time, the corresponding manifest is created in two steps: 1. The directory is traversed recursively and the inode information of all contained files and directories is written to the manifest. 2. The content of all identified files is processed to generate each file's chunk list. This list is part of the definition of a file in the manifest. * The chunk boundaries are identified using our implementation of the FastCDC algorithm. * The hash of each chunk is calculated using the BLAKE3 hash function. * The length and hash of each chunk is appended to the file's chunk list. Prior to this change, when the user mounted a workstation directory on a client, the asset streaming server pushed an intermediate manifest to the gamelet as soon as step 1 was completed. At this point, the FUSE client started serving the virtual file system and was ready to answer `stat` and `readdir` calls. In case the FUSE client received any call that required file contents, such as `read`, it would block the caller until the server completed step 2 above and pushed the final manifest to the client. This works well for large directories (> 100GB) with a reasonable number of files (< 100k). But when dealing with millions of tiny files, creating the full manifest can take several minutes. With this change, we introduce dynamic manifest updates. When the FUSE layer receives an `open` or `readdir` request for a file or directory that is incomplete, it sends an RPC to the workstation about what information is missing from the manifest. The workstation identifies the corresponding file chunker or directory scanner tasks and moves them to the front of the queue. As soon as the task is completed, the workstation pushes an updated intermediate manifest to the client which now includes the information to serve the FUSE request. The queued FUSE request is resumed and returns the result to the caller. While this does not reduce the required time to build the final manifest, it splits up the work into smaller tasks. This allows us to interrupt the current work and prioritize those tasks which are required to handle an incoming request from the client. While this still takes a round-trip to the workstation plus the processing time for the task, an updated manifest is received within a few seconds, which is much better than blocking for several minutes. This latency is only visible when serving data while the manifest is still being created. The situation improves as the manifest creation on the workstation progresses. As soon as the final manifest is pushed, all metadata can be served directly without having to wait for pending tasks.
85 lines
2.6 KiB
C++
85 lines
2.6 KiB
C++
/*
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* Copyright 2022 Google LLC
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef CDC_FUSE_FS_CDC_FUSE_FS_H_
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#define CDC_FUSE_FS_CDC_FUSE_FS_H_
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#ifndef R_OK
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#define R_OK 4
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#endif
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#ifndef W_OK
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#define W_OK 2
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#endif
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#ifndef X_OK
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#define X_OK 1
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#endif
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#include <memory>
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#include "absl/status/status.h"
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#include "cdc_fuse_fs/config_stream_client.h"
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#include "grpcpp/channel.h"
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#include "manifest/manifest_proto_defs.h"
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namespace cdc_ft {
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class DataStoreReader;
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// CdcFuse filesystem constants, exposed for testing.
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namespace internal {
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// Number of hardlinks is not important since the fs is read-only (I think).
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constexpr int kCdcFuseDefaultNLink = 1;
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// Cloudcast user and group id.
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constexpr int kCdcFuseCloudcastUid = 1000;
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constexpr int kCdcFuseCloudcastGid = 1000;
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// Root user and group id.
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constexpr int kCdcFuseRootUid = 0;
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constexpr int kCdcFuseRootGid = 0;
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// Default timeout after which the kernel will assume inodes are stale.
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constexpr double kCdcFuseInodeTimeoutSec = 1.0;
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} // namespace internal
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namespace cdc_fuse_fs {
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// Initializes the CDC FUSE filesystem. Parses the command line, sets up a
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// channel and a session, and optionally forks the process. For valid arguments
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// see fuse_common.h.
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absl::Status Initialize(int argc, char** argv);
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// Sets the client to read configuration updates to |config_client|.
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void SetConfigClient(std::unique_ptr<ConfigStreamClient> config_client);
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// Sets the |data_store_reader| to load data from, initializes FUSE with a
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// manifest for an empty directory, and starts the filesystem. The call does
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// not return until the filesystem finishes running.
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// |consistency_check| defines whether FUSE consistency should be inspected
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// after each manifest update.
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absl::Status Run(DataStoreReader* data_store_reader, bool consistency_check);
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// Releases resources. Should be called when the filesystem finished running.
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void Shutdown();
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// Sets |manifest_id| as a CDC FUSE root.
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absl::Status SetManifest(const ContentIdProto& manifest_id);
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} // namespace cdc_fuse_fs
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} // namespace cdc_ft
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#endif // CDC_FUSE_FS_CDC_FUSE_FS_H_
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