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Allow content-addressable paths to have references

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This adds a command 'nix make-content-addressable' that rewrites the
specified store paths into content-addressable paths. The advantage of
such paths is that 1) they can be imported without signatures; 2) they
can enable deduplication in cases where derivation changes do not
cause output changes (apart from store path hashes).

For example,

  $ nix make-content-addressable -r nixpkgs.cowsay
  rewrote '/nix/store/g1g31ah55xdia1jdqabv1imf6mcw0nb1-glibc-2.25-49' to '/nix/store/48jfj7bg78a8n4f2nhg269rgw1936vj4-glibc-2.25-49'
  ...
  rewrote '/nix/store/qbi6rzpk0bxjw8lw6azn2mc7ynnn455q-cowsay-3.03+dfsg1-16' to '/nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16'

We can then copy the resulting closure to another store without
signatures:

  $ nix copy --trusted-public-keys '' ---to ~/my-nix /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16

In order to support self-references in content-addressable paths,
these paths are hashed "modulo" self-references, meaning that
self-references are zeroed out during hashing. Somewhat annoyingly,
this means that the NAR hash stored in the Nix database is no longer
necessarily equal to the output of "nix hash-path"; for
content-addressable paths, you need to pass the --modulo flag:

  $ nix path-info --json /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16  | jq -r .[].narHash
  sha256:0ri611gdilz2c9rsibqhsipbfs9vwcqvs811a52i2bnkhv7w9mgw

  $ nix hash-path --type sha256 --base32 /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16
  1ggznh07khq0hz6id09pqws3a8q9pn03ya3c03nwck1kwq8rclzs

  $ nix hash-path --type sha256 --base32 /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16 --modulo iq6g2x4q62xp7y7493bibx0qn5w7xz67
  0ri611gdilz2c9rsibqhsipbfs9vwcqvs811a52i2bnkhv7w9mgw
This commit is contained in:
Eelco Dolstra 2018-03-30 00:56:13 +02:00
parent aabf5c86c9
commit 0abb3ad537
16 changed files with 289 additions and 65 deletions
Download patch file Download diff file Expand all files Collapse all files

38
src/libstore/store-api.cc
View file

@ -205,15 +205,27 @@ Path Store::makeOutputPath(const string & id,
}
Path Store::makeFixedOutputPath(bool recursive,
const Hash & hash, const string & name) const
static std::string makeType(string && type, const PathSet & references)
{
return hash.type == htSHA256 && recursive
? makeStorePath("source", hash, name)
: makeStorePath("output:out", hashString(htSHA256,
for (auto & i : references) {
type += ":";
type += i;
}
return type;
}
Path Store::makeFixedOutputPath(bool recursive,
const Hash & hash, const string & name, const PathSet & references) const
{
if (hash.type == htSHA256 && recursive) {
return makeStorePath(makeType("source", references), hash, name);
} else {
assert(references.empty());
return makeStorePath("output:out", hashString(htSHA256,
"fixed:out:" + (recursive ? (string) "r:" : "") +
hash.to_string(Base16) + ":"),
name);
hash.to_string(Base16) + ":"), name);
}
}
@ -224,12 +236,7 @@ Path Store::makeTextPath(const string & name, const Hash & hash,
/* Stuff the references (if any) into the type. This is a bit
hacky, but we can't put them in `s' since that would be
ambiguous. */
string type = "text";
for (auto & i : references) {
type += ":";
type += i;
}
return makeStorePath(type, hash, name);
return makeStorePath(makeType("text", references), hash, name);
}
@ -785,8 +792,9 @@ bool ValidPathInfo::isContentAddressed(const Store & store) const
else if (hasPrefix(ca, "fixed:")) {
bool recursive = ca.compare(6, 2, "r:") == 0;
Hash hash(std::string(ca, recursive ? 8 : 6));
if (references.empty() &&
store.makeFixedOutputPath(recursive, hash, storePathToName(path)) == path)
auto refs = references;
replaceInSet(refs, path, std::string("self"));
if (store.makeFixedOutputPath(recursive, hash, storePathToName(path), refs) == path)
return true;
else
warn();