This fetchers copies a plain directory (i.e. not a Git/Mercurial
repository) to the store (or does nothing if the path is already a
store path).
One use case is to pin the 'nixpkgs' flake used to build the current
NixOS system, and prevent it from being garbage-collected, via a
system registry entry like this:
{
"from": {
"id": "nixpkgs",
"type": "indirect"
},
"to": {
"type": "path",
"path": "/nix/store/rralhl3wj4rdwzjn16g7d93mibvlr521-source",
"lastModified": 1585388205,
"rev": "b0c285807d6a9f1b7562ec417c24fa1a30ecc31a"
},
"exact": true
}
Note the fake "lastModified" and "rev" attributes that ensure that the
flake gives the same evaluation results as the corresponding
Git/GitHub inputs.
(cherry picked from commit 12f9379123)
This provides a pluggable mechanism for defining new fetchers. It adds
a builtin function 'fetchTree' that generalizes existing fetchers like
'fetchGit', 'fetchMercurial' and 'fetchTarball'. 'fetchTree' takes a
set of attributes, e.g.
fetchTree {
type = "git";
url = "https://example.org/repo.git";
ref = "some-branch";
rev = "abcdef...";
}
The existing fetchers are just wrappers around this. Note that the
input attributes to fetchTree are the same as flake input
specifications and flake lock file entries.
All fetchers share a common cache stored in
~/.cache/nix/fetcher-cache-v1.sqlite. This replaces the ad hoc caching
mechanisms in fetchGit and download.cc (e.g. ~/.cache/nix/{tarballs,git-revs*}).
This also adds support for Git worktrees (c169ea5904).
This is useful for finding out what a registry lookup resolves to, e.g
$ nix flake info patchelf
Resolved URL: github:NixOS/patchelf
Locked URL: github:NixOS/patchelf/cd7955af31698c571c30b7a0f78e59fd624d0229
When encountering an unsupported protocol, there's no need to retry.
Chances are, it won't suddenly be supported between retry attempts;
error instead. Otherwise, you see something like the following:
$ nix-env -i -f git://git@github.com/foo/bar
warning: unable to download 'git://git@github.com/foo/bar': Unsupported protocol (1); retrying in 335 ms
warning: unable to download 'git://git@github.com/foo/bar': Unsupported protocol (1); retrying in 604 ms
warning: unable to download 'git://git@github.com/foo/bar': Unsupported protocol (1); retrying in 1340 ms
warning: unable to download 'git://git@github.com/foo/bar': Unsupported protocol (1); retrying in 2685 ms
With this change, you now see:
$ nix-env -i -f git://git@github.com/foo/bar
error: unable to download 'git://git@github.com/foo/bar': Unsupported protocol (1)
When we do something like 'nix flake update --override-input nixpkgs
...', the override is now kept on subsequent calls. (If you don't want
this behaviour, you can use --no-write-lock-file.)
This fetchers copies a plain directory (i.e. not a Git/Mercurial
repository) to the store (or does nothing if the path is already a
store path).
One use case is to pin the 'nixpkgs' flake used to build the current
NixOS system, and prevent it from being garbage-collected, via a
system registry entry like this:
{
"from": {
"id": "nixpkgs",
"type": "indirect"
},
"to": {
"type": "path",
"path": "/nix/store/rralhl3wj4rdwzjn16g7d93mibvlr521-source",
"lastModified": 1585388205,
"rev": "b0c285807d6a9f1b7562ec417c24fa1a30ecc31a"
},
"exact": true
}
Note the fake "lastModified" and "rev" attributes that ensure that the
flake gives the same evaluation results as the corresponding
Git/GitHub inputs.
This allows querying the location of function arguments. E.g.
builtins.unsafeGetAttrPos "x" (builtins.functionArgs ({ x }: null))
=> { column = 57; file = "/home/infinisil/src/nix/inst/test.nix"; line = 1; }
An example use is for pinning the "nixpkgs" entry the system-wide
registry to a particular store path. Inexact matches
(e.g. "nixpkgs/master") should still use the global registry.
One application for this is pinning the 'nixpkgs' flake to the exact
revision used to build the NixOS system, e.g.
{
"flakes": [
{
"from": {
"id": "nixpkgs",
"type": "indirect"
},
"to": {
"owner": "NixOS",
"repo": "nixpkgs",
"type": "github",
"rev": "b0c285807d6a9f1b7562ec417c24fa1a30ecc31a"
}
}
],
"version": 2
}
Using std::filesystem means also having to link with -lstdc++fs on
some platforms and it's hard to discover for what platforms this is
needed. As all the functionality is already implemented as utilities,
use those instead.
Due to fetchGit not checking if rev is an ancestor of ref (there is even
a FIXME comment about it in the code), the cache repo might not have the
ref even though it has the rev. This doesn't matter when submodule =
false, but the submodule = true code blows up because it tries to fetch
the (missing) ref from the cache repo.
Fix this in the simplest way possible: fetch all refs from the local
cache repo when submodules = true.
TODO: Add tests.
The .link file is used as a lock, so I think we should put the
"submodule" attribute in there since turning on submodules creates a new
.link file path.
This is now done in a single pass. Also fixes some issues when
updating flakes with circular dependencies. Finally, when using
'--recreate-lock-file --commit-lock-file', the commit message now
correctly shows the differences.
Sadly 10.15 changed /bin/sh to a shim which executes bash, this means it
can't be used anymore without also opening up the sandbox to allow bash.
Failed to exec /bin/bash as variant for /bin/sh (1: Operation not permitted).
This is used to determine the dependency tree of impure libraries so nix
knows what paths to open in the sandbox. With the less restrictive
defaults it isn't needed anymore.
Running `nix-store --gc --delete` will, as of Nix 2.3.3, simply fail
because the --delete option conflicts with the --delete operation.
$ nix-store --gc --delete
error: only one operation may be specified
Try 'nix-store --help' for more information.
Furthermore, it has been broken since at least Nix 0.16 (which was
released sometime in 2010), which means that any scripts which depend
on it should have been broken at least nine years ago. This commit
simply formally removes the option. There should be no actual difference
in behaviour as far as the user is concerned: it errors with the exact
same error message. The manual has been edited to remove any references
to the (now gone) --delete option.
Other information:
* Path for Nix 0.16 used:
/nix/store/rp3sgmskn0p0pj1ia2qwd5al6f6pinz4-nix-0.16
If you do a fetchTree on a Git repository, whether the result contains
a revCount attribute should not depend on whether that repository
happens to be a shallow clone or not. That would complicate caching a
lot and would be semantically messy. So applying fetchTree/fetchGit to
a shallow repository is now an error unless you pass the attribute
'shallow = true'. If 'shallow = true', we don't return revCount, even
if the repository is not actually shallow.
Note that Nix itself is not doing shallow clones at the moment. But it
could do so as an optimisation if the user specifies 'shallow = true'.
Issue #2988.
In
nix-instantiate --dry-run '<nixpkgs/nixos/release-combined.nix>' -A nixos.tests.simple.x86_64-linux
this reduces time spent in unparse() from 9.15% to 4.31%. The main
culprit was appending characters one at a time to the destination
string. Even though the string has enough capacity, push_back() still
needs to check this on every call.
Note: like 'nix run', and unlike 'nix-shell', this takes an argv
vector rather than a shell command. So
nix dev-shell -c 'echo $PATH'
doesn't work. Instead you need to do
nix dev-shell -c bash -c 'echo $PATH'
The problem fixed: each nix-shell invocation creates a new temporary
directory (`/tmp/nix-shell-*`) and never cleans up.
And while I'm here, shellescape all variables inlined into the rcfile.
See what might happen without escaping:
$ export TZ="';echo pwned'"
$ nix-shell -p hello --run hello
pwned
Hello, world!
Worktrees[1] are a feature of git which allow you to check out a ref in
a different directory.
While playing around with flakes I realized that git repositories in a
worktree checkout break when trying to build a flake:
```
$ git worktree add ../nixpkgs-flakes nixpkgs-flakes
$ cd ../nixpkgs-flakes
$ nix build .#hello
error: opening directory '/home/ma27/Projects/nixpkgs-flakes/.git/refs/heads': Not a directory
```
This issue has been fixed by determining with `git rev-parse --git-common-dir`
where the actual `.git` directory is.
Please note that this issue only exists on the `flakes` branch, fetching
worktree checkouts with Nix master seems to work fine.
[1] https://git-scm.com/docs/git-worktree
The ssh client is lazily started by the first worker thread, that
requires a ssh connection. To avoid the ssh client to be killed, when
the worker process is stopped, do not set PR_SET_PDEATHSIG.
This allows all supported fetchers to be used, e.g.
builtins.fetchTree {
type = "github";
owner = "NixOS";
repo = "nix";
rev = "d4df99a3349cf2228a8ee78dea320afef86eb3ba";
}
Brings the functionality of ssh-ng:// in sync with the legacy ssh://
implementation. Specifying the remote store uri enables various useful
things. eg.
$ nix copy --to ssh-ng://cache?remote-store=file://mnt/cache --all
This improves reproducibility and may be faster than fetching from the
original source (especially for git/hg inputs, but probably also for
github inputs - our binary cache is probably faster than GitHub's
dynamically generated tarballs).
Unfortunately this doesn't work for the top-level flake since even if
we know the NAR hash of the tree, we don't know the other tree
attributes such as revCount and lastModified.
Fixes#3253.
This copies a flake and all its inputs recursively to a store (e.g. a
binary cache). This is intended to enable long-term reproducibility
for flakes. However this will also require #3253.
Example:
$ nix flake archive --json --to file:///tmp/my-cache nixops
{"path":"/nix/store/272igzkgl1gdzmabsjvb2kb2zqbphb3p-source","inputs":{"nixops-aws":{"path":"/nix/store/ybcykw13gr7iq1pzg18iyibbcv8k9q1v-source","inputs":{}},"nixops-hetzner":{"path":"/nix/store/6yn0205x3nz55w8ms3335p2841javz2d-source","inputs":{}},"nixpkgs":{"path":"/nix/store/li3lkr2ajrzphqqz3jj2avndnyd3i5lc-source","inputs":{}}}}
$ ll /tmp/my-cache
total 16
-rw-r--r-- 1 eelco users 403 Jan 30 01:01 272igzkgl1gdzmabsjvb2kb2zqbphb3p.narinfo
-rw-r--r-- 1 eelco users 403 Jan 30 01:01 6yn0205x3nz55w8ms3335p2841javz2d.narinfo
-rw-r--r-- 1 eelco users 408 Jan 30 01:01 li3lkr2ajrzphqqz3jj2avndnyd3i5lc.narinfo
drwxr-xr-x 2 eelco users 6 Jan 30 01:01 nar
-rw-r--r-- 1 eelco users 21 Jan 30 01:01 nix-cache-info
-rw-r--r-- 1 eelco users 404 Jan 30 01:01 ybcykw13gr7iq1pzg18iyibbcv8k9q1v.narinfo
Fixes#3336.
Typical usage:
$ nix flake update ~/Misc/eelco-configurations/hagbard --update-input nixpkgs
to update the 'nixpkgs' input of a flake while leaving every other
input unchanged.
The argument is an input path, so you can do e.g. '--update-input
dwarffs/nixpkgs' to update an input of an input.
Fixes#2928.
Added a flag --no-update-lock-file to barf if the lock file needs any
changes. This is useful for CI systems if you're building a
checkout. Fixes#2947.
Renamed --no-save-lock-file to --no-write-lock-file. It is now a fatal
error if the lock file needs changes but --no-write-lock-file is not
given.
E.g.
$ nix flake update ~/Misc/eelco-configurations/hagbard \
--override-input 'dwarffs/nixpkgs' ../my-nixpkgs
overrides the 'nixpkgs' input of the 'dwarffs' input of the top-level
flake.
Fixes#2837.
When computing a lock file, we now respect the lock files of flake
inputs. This is important for usability / reproducibility. For
example, the 'nixops' flake depends on the 'nixops-aws' and
'nixops-hetzner' repositories. So when the 'nixops' flake is used in
another flake, we want the versions of 'nixops-aws' and
'nixops-hetzner' locked by the the 'nixops' flake because those
presumably have been tested.
This can lead to a proliferation of versions of flakes like 'nixpkgs'
(since every flake's lock file could depend on a different version of
'nixpkgs'). This is not a major issue when using Nixpkgs overlays or
NixOS modules, since then the top-level flake composes those
overlays/modules into *its* version of Nixpkgs and all other versions
are ignored. Lock file computation has been made a bit more lazy so it
won't try to fetch all those versions of 'nixpkgs'.
However, in case it's necessary to minimize flake versions, there now
are two input attributes that allow this. First, you can copy an input
from another flake, as follows:
inputs.nixpkgs.follows = "dwarffs/nixpkgs";
This states that the calling flake's 'nixpkgs' input shall be the same
as the 'nixpkgs' input of the 'dwarffs' input.
Second, you can override inputs of inputs:
inputs.nixpkgs.url = github:edolstra/nixpkgs/<hash>;
inputs.nixops.inputs.nixpkgs.url = github:edolstra/nixpkgs/<hash>;
or equivalently, using 'follows':
inputs.nixpkgs.url = github:edolstra/nixpkgs/<hash>;
inputs.nixops.inputs.nixpkgs.follows = "nixpkgs";
This states that the 'nixpkgs' input of the 'nixops' input shall be
the same as the calling flake's 'nixpkgs' input.
Finally, at '-v' Nix now prints the changes to the lock file, e.g.
$ nix flake update ~/Misc/eelco-configurations/hagbard
inputs of flake 'git+file:///home/eelco/Misc/eelco-configurations?subdir=hagbard' changed:
updated 'nixpkgs': 'github:edolstra/nixpkgs/7845bf5f4b3013df1cf036e9c9c3a55a30331db9' -> 'github:edolstra/nixpkgs/03f3def66a104a221aac8b751eeb7075374848fd'
removed 'nixops'
removed 'nixops/nixops-aws'
removed 'nixops/nixops-hetzner'
removed 'nixops/nixpkgs'
Fixes
error: derivation '/nix/store/klivma7r7h5lndb99f7xxmlh5whyayvg-zlib-1.2.11.drv' has incorrect output '/nix/store/fv98nnx5ykgbq8sqabilkgkbc4169q05-zlib-1.2.11-dev', should be '/nix/store/adm7pilzlj3z5k249s8b4wv3scprhzi1-zlib-1.2.11-dev'
Includes the expression of the condition in the assertion message if
the assertion failed, making assertions much easier to debug. eg.
error: assertion (withPython -> (python2Packages != null)) failed at pkgs/tools/security/nmap/default.nix:11:1
As fromTOML supports \u and \U escapes, bring fromJSON on par. As JSON defaults
to UTF-8 encoding (every JSON parser must support UTF-8), this change parses the
`\u hex hex hex hex` sequence (\u followed by 4 hexadecimal digits) into an
UTF-8 representation.
Add a test to verify correct parsing, using all escape sequences from json.org.
This prevents them from being inlined. On gcc 9, this reduces the
stack size needed for
nix-instantiate '<nixpkgs>' -A texlive.combined.scheme-full --dry-run
from 12.9 MiB to 4.8 MiB.
Having a colon in the path may cause issues, and having the hash
function indicated isn't actually necessary. We now verify the path
format in the tests to prevent regressions.
Before, we would get:
[deploy@bastion:~]$ nix-store -r /nix/store/grfnl76cahwls0igd2by2pqv0dimi8h2-nixos-system-eris-19.09.20191213.03f3def.drv
these derivations will be built:
/nix/store/3ka4ihvwh6wsyhpd2qa9f59506mnxvx1-initrd-linux-4.19.88.drv
/nix/store/ssxwmll7v21did1c8j027q0m8w6pg41i-unit-prometheus-alertmanager-irc-notifier.service.drv
/nix/store/mvyvkj46ay7pp7b1znqbkck2mq98k0qd-unit-script-network-local-commands-start.drv
/nix/store/vsl1y9mz38qfk6pyirjwnfzfggz5akg6-unit-network-local-commands.service.drv
/nix/store/wi5ighfwwb83fdmav6z6n2fw6npm9ffl-unit-prometheus-hydra-exporter.service.drv
/nix/store/x0qkv535n75pbl3xn6nn1w7qkrg9wwyg-unit-prometheus-packet-sd.service.drv
/nix/store/lv491znsjxdf51xnfxh9ld7r1zg14d52-unit-script-packet-sd-env-key-pre-start.drv
/nix/store/nw4nzlca49agsajvpibx7zg5b873gk9f-unit-script-packet-sd-env-key-start.drv
/nix/store/x674wwabdwjrkhnykair4c8mpxa9532w-unit-packet-sd-env-key.service.drv
/nix/store/ywivz64ilb1ywlv652pkixw3vxzfvgv8-unit-wireguard-wg0.service.drv
/nix/store/v3b648293g3zl8pnn0m1345nvmyd8dwb-unit-script-acme-selfsigned-status.nixos.org-start.drv
/nix/store/zci5d3zvr6fgdicz6k7jjka6lmx0v3g4-unit-acme-selfsigned-status.nixos.org.service.drv
/nix/store/f6pwvnm63d0kw5df0v7sipd1rkhqxk5g-system-units.drv
/nix/store/iax8071knxk9c7krpm9jqg0lcrawf4lc-etc.drv
/nix/store/grfnl76cahwls0igd2by2pqv0dimi8h2-nixos-system-eris-19.09.20191213.03f3def.drv
error: invalid file name 'closure-init-0' in 'exportReferencesGraph'
This was tough to debug, I didn't figure out which one was broken until I did:
nix-store -r /nix/store/grfnl76cahwls0igd2by2pqv0dimi8h2-nixos-system-eris-19.09.20191213.03f3def.drv 2>&1 | grep nix/store | xargs -n1 nix-store -r
and then looking at the remaining build graph:
$ nix-store -r /nix/store/grfnl76cahwls0igd2by2pqv0dimi8h2-nixos-system-eris-19.09.20191213.03f3def.drv
these derivations will be built:
/nix/store/3ka4ihvwh6wsyhpd2qa9f59506mnxvx1-initrd-linux-4.19.88.drv
/nix/store/grfnl76cahwls0igd2by2pqv0dimi8h2-nixos-system-eris-19.09.20191213.03f3def.drv
error: invalid file name 'closure-init-0' in 'exportReferencesGraph'
and knowing the initrd build is before the system, then:
$ nix show-derivation /nix/store/3ka4ihvwh6wsyhpd2qa9f59506mnxvx1-initrd-linux-4.19.88.drv
{
"/nix/store/3ka4ihvwh6wsyhpd2qa9f59506mnxvx1-initrd-linux-4.19.88.drv": {
[...]
"exportReferencesGraph": "closure-init-0 /nix/store/...-stage-1-init.sh closure-mdadm.conf-1 /nix/store/...-mdadm.conf closure-ubuntu.conf-2 ...",
[...]
}
}
I then searched the repo for "in 'exportReferencesGraph'", found this
recently updated regex, and realized it was missing a "-".
Before:
$ nix-channel --update
unpacking channels...
warning: SQLite database '/nix/var/nix/db/db.sqlite' is busy (SQLITE_PROTOCOL)
warning: SQLite database '/nix/var/nix/db/db.sqlite' is busy (SQLITE_PROTOCOL)
warning: SQLite database '/nix/var/nix/db/db.sqlite' is busy (SQLITE_PROTOCOL)
warning: SQLite database '/nix/var/nix/db/db.sqlite' is busy (SQLITE_PROTOCOL)
warning: SQLite database '/nix/var/nix/db/db.sqlite' is busy (SQLITE_PROTOCOL)
After:
$ inst/bin/nix-channel --update
unpacking channels...
created 1 symlinks in user environment
I've seen complaints that "sandbox" caused problems under WSL but I'm
having no problems. I think recent changes could have fixed the issue.
This allows overriding the priority of substituters, e.g.
$ nix-store --store ~/my-nix/ -r /nix/store/df3m4da96d84ljzxx4mygfshm1p0r2n3-geeqie-1.4 \
--substituters 'http://cache.nixos.org?priority=100 daemon?priority=10'
Fixes#3264.
There is no termination condition for evaluation of cyclical
expression paths which can lead to infinite loops. This addresses
one spot in the parser in a similar fashion as utils.cc/canonPath
does.
This issue can be reproduced by something like:
```
ln -s a b
ln -s b a
nix-instantiate -E 'import ./a'
```
If the `throw` is reached, this means that execvp into `ssh` wasn’t
successful. We can hint at a usual problem, which is a missing `ssh`
executable.
Test with:
```
env PATH= ./result/bin/nix-copy-closure --builders '' unusedhost
```
and the bash version with
```
env PATH= ./result/bin/nix-copy-closure --builders '' localhost
```
Most functions now take a StorePath argument rather than a Path (which
is just an alias for std::string). The StorePath constructor ensures
that the path is syntactically correct (i.e. it looks like
<store-dir>/<base32-hash>-<name>). Similarly, functions like
buildPaths() now take a StorePathWithOutputs, rather than abusing Path
by adding a '!<outputs>' suffix.
Note that the StorePath type is implemented in Rust. This involves
some hackery to allow Rust values to be used directly in C++, via a
helper type whose destructor calls the Rust type's drop()
function. The main issue is the dynamic nature of C++ move semantics:
after we have moved a Rust value, we should not call the drop function
on the original value. So when we move a value, we set the original
value to bitwise zero, and the destructor only calls drop() if the
value is not bitwise zero. This should be sufficient for most types.
Also lots of minor cleanups to the C++ API to make it more modern
(e.g. using std::optional and std::string_view in some places).
The FunctionCallTrace object consumes a few hundred bytes of stack
space, even when tracing is disabled. This was causing stack overflows:
$ nix-instantiate '<nixpkgs> -A texlive.combined.scheme-full --dry-run
error: stack overflow (possible infinite recursion)
This is with the default stack size of 8 MiB.
Putting the object on the heap reduces stack usage to < 5 MiB.
https://hydra.nixos.org/build/107467517
Seems that on i686-linux, gcc and rustc disagree on how to return
1-word structs: gcc has the caller pass a pointer to the result, while
rustc has the callee return the result in a register. Work around this
by using a bare pointer.
This replaces the '(...)' installable syntax, which is not very
discoverable. The downside is that you can't have multiple expressions
or mix expressions and other installables.
Also, fetchGit now runs in O(1) memory since we pipe the output of
'git archive' directly into unpackTarball() (rather than first reading
it all into memory).
We can now convert Rust Errors to C++ exceptions. At the Rust->C++ FFI
boundary, Result<T, Error> will cause Error to be converted to and
thrown as a C++ exception.
E.g.
$ nix-build '<nixpkgs>' -A hello --experimental-features no-url-literals
error: URL literals are disabled, at /nix/store/vsjamkzh15r3c779q2711az826hqgvzr-nixpkgs-20.03pre194957.bef773ed53f/nixpkgs/pkgs/top-level/all-packages.nix:1236:11
Helps with implementing https://github.com/NixOS/rfcs/pull/45.
A corrupt entry in .links prevents adding a fixed version of that file
to the store in any path. The user experience is that corruption
present in the store 'spreads' to new paths added to the store:
(With store optimisation enabled)
1. A file in the store gets corrupted somehow (eg: filesystem bug).
2. The user tries to add a thing to the store which contains a good copy
of the corrupted file.
3. The file being added to the store is hashed, found to match the bad
.links entry, and is replaced by a link to the bad .links entry.
(The .links entry's hash is not verified during add -- this would
impose a substantial performance burden.)
4. The user observes that the thing in the store that is supposed to be
a copy of what they were trying to add is not a correct copy -- some
files have different contents! Running "nix-store --verify
--check-contents --repair" does not fix the problem.
This change makes "nix-store --verify --check-contents --repair" fix
this problem. Bad .links entries are simply removed, allowing future
attempts to insert a good copy of the file to succeed.
This doesn't work anymore since `packages` was removed from the
`nixpkgs`-fork with flake support[1], now it's only possible to refer to
pkgs via `legacyPackages`.
[1] 49c9b71e4c
The store path is not enough. For example, when we build a dirty tree,
commit, and build the clean tree, a re-evaluation is necessary because
the flake may depend on the lastModified or revCount attributes.
Derivations that want to use recursion should now set
requiredSystemFeatures = [ "recursive-nix" ];
to make the daemon socket appear.
Also, Nix should be configured with "experimental-features =
recursive-nix".
This allows Nix builders to call Nix to build derivations, with some
limitations.
Example:
let nixpkgs = fetchTarball channel:nixos-18.03; in
with import <nixpkgs> {};
runCommand "foo"
{
buildInputs = [ nix jq ];
NIX_PATH = "nixpkgs=${nixpkgs}";
}
''
hello=$(nix-build -E '(import <nixpkgs> {}).hello.overrideDerivation (args: { name = "hello-3.5"; })')
$hello/bin/hello
mkdir -p $out/bin
ln -s $hello/bin/hello $out/bin/hello
nix path-info -r --json $hello | jq .
''
This derivation makes a recursive Nix call to build GNU Hello and
symlinks it from its $out, i.e.
# ll ./result/bin/
lrwxrwxrwx 1 root root 63 Jan 1 1970 hello -> /nix/store/s0awxrs71gickhaqdwxl506hzccb30y5-hello-3.5/bin/hello
# nix-store -qR ./result
/nix/store/hwwqshlmazzjzj7yhrkyjydxamvvkfd3-glibc-2.26-131
/nix/store/s0awxrs71gickhaqdwxl506hzccb30y5-hello-3.5
/nix/store/sgmvvyw8vhfqdqb619bxkcpfn9lvd8ss-foo
This is implemented as follows:
* Before running the outer builder, Nix creates a Unix domain socket
'.nix-socket' in the builder's temporary directory and sets
$NIX_REMOTE to point to it. It starts a thread to process
connections to this socket. (Thus you don't need to have nix-daemon
running.)
* The daemon thread uses a wrapper store (RestrictedStore) to keep
track of paths added through recursive Nix calls, to implement some
restrictions (see below), and to do some censorship (e.g. for
purity, queryPathInfo() won't return impure information such as
signatures and timestamps).
* After the build finishes, the output paths are scanned for
references to the paths added through recursive Nix calls (in
addition to the inputs closure). Thus, in the example above, $out
has a reference to $hello.
The main restriction on recursive Nix calls is that they cannot do
arbitrary substitutions. For example, doing
nix-store -r /nix/store/kmwd1hq55akdb9sc7l3finr175dajlby-hello-2.10
is forbidden unless /nix/store/kmwd... is in the inputs closure or
previously built by a recursive Nix call. This is to prevent
irreproducible derivations that have hidden dependencies on
substituters or the current store contents. Building a derivation is
fine, however, and Nix will use substitutes if available. In other
words, the builder has to present proof that it knows how to build a
desired store path from scratch by constructing a derivation graph for
that path.
Probably we should also disallow instantiating/building fixed-output
derivations (specifically, those that access the network, but
currently we have no way to mark fixed-output derivations that don't
access the network). Otherwise sandboxed derivations can bypass
sandbox restrictions and access the network.
When sandboxing is enabled, we make paths appear in the sandbox of the
builder by entering the mount namespace of the builder and
bind-mounting each path. This is tricky because we do a pivot_root()
in the builder to change the root directory of its mount namespace,
and thus the host /nix/store is not visible in the mount namespace of
the builder. To get around this, just before doing pivot_root(), we
branch a second mount namespace that shares its /nix/store mountpoint
with the parent.
Recursive Nix currently doesn't work on macOS in sandboxed mode
(because we can't change the sandbox policy of a running build) and in
non-root mode (because setns() barfs).
Julian Stecklina
Robert Hensing
Maximilian Bosch
Yorick
edef
puck