mirror of
https://github.com/privatevoid-net/nix-super.git
synced 2024-11-16 03:06:17 +02:00
eb7d7780b1
This is needed to avoid this https://github.com/mesonbuild/meson/issues/13774 when we go back to making our subproject directory `src`.
79 lines
3 KiB
Markdown
79 lines
3 KiB
Markdown
# Store Path
|
||
|
||
> **Example**
|
||
>
|
||
> `/nix/store/a040m110amc4h71lds2jmr8qrkj2jhxd-git-2.38.1`
|
||
>
|
||
> A rendered store path
|
||
|
||
Nix implements references to [store objects](./index.md#store-object) as *store paths*.
|
||
|
||
Think of a store path as an [opaque], [unique identifier]:
|
||
The only way to obtain store path is by adding or building store objects.
|
||
A store path will always reference exactly one store object.
|
||
|
||
[opaque]: https://en.m.wikipedia.org/wiki/Opaque_data_type
|
||
[unique identifier]: https://en.m.wikipedia.org/wiki/Unique_identifier
|
||
|
||
Store paths are pairs of
|
||
|
||
- A 20-byte digest for identification
|
||
- A symbolic name for people to read
|
||
|
||
> **Example**
|
||
>
|
||
> - Digest: `b6gvzjyb2pg0kjfwrjmg1vfhh54ad73z`
|
||
> - Name: `firefox-33.1`
|
||
|
||
To make store objects accessible to operating system processes, stores have to expose store objects through the file system.
|
||
|
||
A store path is rendered to a file system path as the concatenation of
|
||
|
||
- [Store directory](#store-directory) (typically `/nix/store`)
|
||
- Path separator (`/`)
|
||
- Digest rendered in a custom variant of [Base32](https://en.wikipedia.org/wiki/Base32) (20 arbitrary bytes become 32 ASCII characters)
|
||
- Hyphen (`-`)
|
||
- Name
|
||
|
||
> **Example**
|
||
>
|
||
> ```
|
||
> /nix/store/b6gvzjyb2pg0kjfwrjmg1vfhh54ad73z-firefox-33.1
|
||
> |--------| |------------------------------| |----------|
|
||
> store directory digest name
|
||
> ```
|
||
|
||
Exactly how the digest is calculated depends on the type of store path.
|
||
Store path digests are *supposed* to be opaque, and so for most operations, it is not necessary to know the details.
|
||
That said, the manual has a full [specification of store path digests](@docroot@/protocols/store-path.md).
|
||
|
||
## Store Directory
|
||
|
||
Every [Nix store](./index.md) has a store directory.
|
||
|
||
Not every store can be accessed through the file system.
|
||
But if the store has a file system representation, the store directory contains the store’s [file system objects], which can be addressed by [store paths](#store-path).
|
||
|
||
[file system objects]: ./file-system-object.md
|
||
|
||
This means a store path is not just derived from the referenced store object itself, but depends on the store that the store object is in.
|
||
|
||
> **Note**
|
||
>
|
||
> The store directory defaults to `/nix/store`, but is in principle arbitrary.
|
||
|
||
It is important which store a given store object belongs to:
|
||
Files in the store object can contain store paths, and processes may read these paths.
|
||
Nix can only guarantee referential integrity if store paths do not cross store boundaries.
|
||
|
||
Therefore one can only copy store objects to a different store if
|
||
|
||
- The source and target stores' directories match
|
||
|
||
or
|
||
|
||
- The store object in question has no references, that is, contains no store paths
|
||
|
||
One cannot copy a store object to a store with a different store directory.
|
||
Instead, it has to be rebuilt, together with all its dependencies.
|
||
It is in general not enough to replace the store directory string in file contents, as this may render executables unusable by invalidating their internal offsets or checksums.
|