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| author | John Ericson <John.Ericson@Obsidian.Systems> | 2022-04-19 01:44:02 -0400 |
|---|---|---|
| committer | Valentin Gagarin <valentin.gagarin@tweag.io> | 2022-08-04 12:37:46 +0200 |
| commit | e4eea5e84e78cc57859cca9295da450258e8f55b (patch) | |
| tree | 395c54e752f7c79122f91d14d5ca3f481781eecb /doc/manual | |
| parent | b98dc3b19c62abb3b8edc778cee0ac8234c5577d (diff) | |
Include abstract syntax based on the thesis for FSOs
See https://edolstra.github.io/pubs/phd-thesis.pdf, page 91.
Diffstat (limited to 'doc/manual')
| -rw-r--r-- | doc/manual/src/design/store/objects.md | 23 |
1 files changed, 22 insertions, 1 deletions
diff --git a/doc/manual/src/design/store/objects.md b/doc/manual/src/design/store/objects.md index 38c73bc7a..0f3d2a499 100644 --- a/doc/manual/src/design/store/objects.md +++ b/doc/manual/src/design/store/objects.md @@ -9,6 +9,16 @@ A store object is the pair of ## File system objects The Nix store uses a simple filesystem model. + + data FileSystemObject + = Regular Executable ByteString + | Directory (Map FileName FSO) + | SymLink ByteString + + data Executable + = Executable + | NonExecutable + In particular, every file system object falls into these three cases: - File: an executable flag, and arbitrary data @@ -26,10 +36,21 @@ A bare file or symlink as the "root" file system object is allowed. This is close to Git's model, but with one crucial difference: Git puts the "permission" info within the directory map's values instead of making it part of the file (blob, in it's parlance) object. + data GitObject + = Blob ByteString + | Tree (Map FileName (Persission, FSO)) + + data Persission + = Directory -- IFF paired with tree + -- Iff paired with blob, one of: + | RegFile + | ExecutableFile + | Symlink + So long as the root object is a directory, the representations are isomorphic. There is no "wiggle room" the git way since whenever the permission info wouldn't matter (e.g. the child object being mapped to is a directory), the permission info must be a sentinel value. -However, if the root object is a file, there is loss of fidelity. +However, if the root object is a blob, there is loss of fidelity. Since the permission info is used to distinguish executable files, non-executable files, and symlinks, but there isn't a "parent" directory of the root to contain that info, these 3 cases cannot be distinguished. Git's model matches Unix tradition, but Nix's model is more natural. |