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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
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21
src/libstore/local-store.cc
View file

@ -5,6 +5,7 @@
#include "worker-protocol.hh"
#include "derivations.hh"
#include "nar-info.hh"
#include "references.hh"
#include <iostream>
#include <algorithm>
@ -1009,17 +1010,21 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
/* While restoring the path from the NAR, compute the hash
of the NAR. */
HashSink hashSink(htSHA256);
std::unique_ptr<AbstractHashSink> hashSink;
if (info.ca == "")
hashSink = std::make_unique<HashSink>(htSHA256);
else
hashSink = std::make_unique<HashModuloSink>(htSHA256, storePathToHash(info.path));
LambdaSource wrapperSource([&](unsigned char * data, size_t len) -> size_t {
size_t n = source.read(data, len);
hashSink(data, n);
(*hashSink)(data, n);
return n;
});
restorePath(realPath, wrapperSource);
auto hashResult = hashSink.finish();
auto hashResult = hashSink->finish();
if (hashResult.first != info.narHash)
throw Error("hash mismatch importing path '%s';\n wanted: %s\n got: %s",
@ -1241,7 +1246,15 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
/* Check the content hash (optionally - slow). */
printMsg(lvlTalkative, format("checking contents of '%1%'") % i);
HashResult current = hashPath(info->narHash.type, toRealPath(i));
std::unique_ptr<AbstractHashSink> hashSink;
if (info->ca == "")
hashSink = std::make_unique<HashSink>(info->narHash.type);
else
hashSink = std::make_unique<HashModuloSink>(info->narHash.type, storePathToHash(info->path));
dumpPath(toRealPath(i), *hashSink);
auto current = hashSink->finish();
if (info->narHash != nullHash && info->narHash != current.first) {
printError(format("path '%1%' was modified! "