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.
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.
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).
The intent of the code was that if the window size cannot be determined,
it would be treated as having the maximum possible size. Because of a
missing assignment, it was actually treated as having a width of 0.
The reason the width could not be determined was because it was obtained
from stdout, not stderr, even though the printing was done to stderr.
This commit addresses both issues.
Add missing docstring on InstallableCommand. Also, some of these were wrapped
when they're right next to a line longer than the unwrapped line, so we can just
unwrap them to save vertical space.
Fixes the following warning and the indicate potential issue:
src/libstore/worker-protocol.hh:66:1: warning: class 'Source' was previously declared as a struct; this is valid, but may result in linker errors
under the Microsoft C++ ABI [-Wmismatched-tags]
(cherry picked from commit 6e1bb04870b1b723282d32182af286646f13bf3c)
This is an alternative to the IN_NIX_SHELL environment variable,
allowing the expression to adapt itself to nix-shell without
triggering those adaptations when used as a dependency of another
shell.
Closes#3147
