mirror of
https://github.com/privatevoid-net/nix-super.git
synced 2024-11-16 03:06:17 +02:00
72 lines
2.6 KiB
C++
72 lines
2.6 KiB
C++
#pragma once
|
|
///@file
|
|
|
|
#include "local-fs-store.hh"
|
|
|
|
namespace nix {
|
|
|
|
/**
|
|
* Mix-in class for implementing permanent roots as a pair of a direct
|
|
* (strong) reference and indirect weak reference to the first
|
|
* reference.
|
|
*
|
|
* See methods for details on the operations it represents.
|
|
*
|
|
* @note
|
|
* To understand the purpose of this class, it might help to do some
|
|
* "closed-world" rather than "open-world" reasoning, and consider the
|
|
* problem it solved for us. This class was factored out from
|
|
* `LocalFSStore` in order to support the following table, which
|
|
* contains 4 concrete store types (non-abstract classes, exposed to the
|
|
* user), and how they implemented the two GC root methods:
|
|
*
|
|
* @note
|
|
* | | `addPermRoot()` | `addIndirectRoot()` |
|
|
* |-------------------|-----------------|---------------------|
|
|
* | `LocalStore` | local | local |
|
|
* | `UDSRemoteStore` | local | remote |
|
|
* | `SSHStore` | doesn't have | doesn't have |
|
|
* | `MountedSSHStore` | remote | doesn't have |
|
|
*
|
|
* @note
|
|
* Note how only the local implementations of `addPermRoot()` need
|
|
* `addIndirectRoot()`; that is what this class enforces. Without it,
|
|
* and with `addPermRoot()` and `addIndirectRoot()` both `virtual`, we
|
|
* would accidentally be allowing for a combinatorial explosion of
|
|
* possible implementations many of which make no sense. Having this and
|
|
* that invariant enforced cuts down that space.
|
|
*/
|
|
struct IndirectRootStore : public virtual LocalFSStore
|
|
{
|
|
inline static std::string operationName = "Indirect GC roots registration";
|
|
|
|
/**
|
|
* Implementation of `LocalFSStore::addPermRoot` where the permanent
|
|
* root is a pair of
|
|
*
|
|
* - The user-facing symlink which all implementations must create
|
|
*
|
|
* - An additional weak reference known as the "indirect root" that
|
|
* points to that symlink.
|
|
*
|
|
* The garbage collector will automatically remove the indirect root
|
|
* when it finds that the symlink has disappeared.
|
|
*
|
|
* The implementation of this method is concrete, but it delegates
|
|
* to `addIndirectRoot()` which is abstract.
|
|
*/
|
|
Path addPermRoot(const StorePath & storePath, const Path & gcRoot) override final;
|
|
|
|
/**
|
|
* Add an indirect root, which is a weak reference to the
|
|
* user-facing symlink created by `addPermRoot()`.
|
|
*
|
|
* @param path user-facing and user-controlled symlink to a store
|
|
* path.
|
|
*
|
|
* The form this weak-reference takes is implementation-specific.
|
|
*/
|
|
virtual void addIndirectRoot(const Path & path) = 0;
|
|
};
|
|
|
|
}
|