File a minor race condition in the backup realm file action #7341
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Pull Request Test Coverage Report for Build thomas.goyne_172Details
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michael-wb
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Feb 14, 2024
| @@ -193,6 +193,13 @@ void migrate_to_v7(std::shared_ptr<Realm> old_realm, std::shared_ptr<Realm> real | |||
| } | |||
| } | |||
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| void migrate_to_v8(Realm&, Realm& realm) | |||
| { | |||
| if (auto app_metadata_table = realm.read_group().get_table("class_AppMetadata")) { | |||
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Will we need to do anything to convert the fileActionMetadata entries to the new format without the partition and identity fields? If so, maybe add a comment somewhere in this function.
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No, removing columns no longer present in the schema is done automatically. It just requires a schema version bump since it's a destructive change.
Checking if the destination exists before copying is a race condition as the file can be created in between the check and the copy. Instead we should attempt to copy without overwriting the target if it exists.
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Checking if the destination of a copy exists before trying to copy is a TOCTOU race because the state of the filesystem can change between when we check and when we perform the copy. We should instead just open the target file and not perform the copy if it already existed.
clonefile()is an APFS feature to perform copy-on-write clones of files. This is much faster, and makes it so that the copy and then delete original that we do doesn't consume extra disk space. It's not always supported, so we fall back to manual copying if it fails.Two of the file action fields weren't actually used for anything.