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Support opening local store with database on read-only filesystem (#8356)

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Previously it was not possible to open a local store when its database is on a read-only filesystem. Obviously a store on a read-only filesystem cannot be modified, but it would still be useful to be able to query it.

This change adds a new read-only setting to LocalStore. When set to true, Nix will skip operations that fail when the database is on a read-only filesystem (acquiring big-lock, schema migration, etc), and the store database will be opened in immutable mode.

Co-authored-by: Ben Radford <benradf@users.noreply.github.com>
Co-authored-by: cidkidnix <cidkidnix@protonmail.com>
Co-authored-by: Dylan Green <67574902+cidkidnix@users.noreply.github.com>
Co-authored-by: John Ericson <git@JohnEricson.me>
Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
This commit is contained in:
Ben Radford 2023-06-20 10:34:09 +01:00 • committed by GitHub
parent 3910430b9d
commit 6ae35534b7
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9 changed files with 144 additions and 16 deletions
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21
src/libstore/local-store.hh
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@ -46,6 +46,23 @@ struct LocalStoreConfig : virtual LocalFSStoreConfig
"require-sigs",
"Whether store paths copied into this store should have a trusted signature."};
Setting<bool> readOnly{(StoreConfig*) this,
false,
"read-only",
R"(
Allow this store to be opened when its [database](@docroot@/glossary.md#gloss-nix-database) is on a read-only filesystem.
Normally Nix will attempt to open the store database in read-write mode, even for querying (when write access is not needed), causing it to fail if the database is on a read-only filesystem.
Enable read-only mode to disable locking and open the SQLite database with the [`immutable` parameter](https://www.sqlite.org/c3ref/open.html) set.
> **Warning**
> Do not use this unless the filesystem is read-only.
>
> Using it when the filesystem is writable can cause incorrect query results or corruption errors if the database is changed by another process.
> While the filesystem the database resides on might appear to be read-only, consider whether another user or system might have write access to it.
)"};
const std::string name() override { return "Local Store"; }
std::string doc() override;
@ -269,6 +286,10 @@ public:
private:
/**
* Retrieve the current version of the database schema.
* If the database does not exist yet, the version returned will be 0.
*/
int getSchema();
void openDB(State & state, bool create);