lix/src/nix/run.cc
John Ericson bc23a44c54 Make command infra less stateful and more regular
Already, we had classes like `BuiltPathsCommand` and `StorePathsCommand`
which provided alternative `run` virtual functions providing the
implementation with more arguments. This was a very nice and easy way to
make writing command; just fill in the virtual functions and it is
fairly clear what to do.

However, exception to this pattern were `Installable{,s}Command`. These
two classes instead just had a field where the installables would be
stored, and various side-effecting `prepare` and `load` machinery too
fill them in. Command would wish out those fields.

This isn't so clear to use.

What this commit does is make those command classes like the others,
with richer `run` functions.

Not only does this restore the pattern making commands easier to write,
it has a number of other benefits:

- `prepare` and `load` are gone entirely! One command just hands just
  hands off to the next.

- `useDefaultInstallables` because `defaultInstallables`. This takes
  over `prepare` for the one case that needs it, and provides enough
  flexiblity to handle `nix repl`'s idiosyncratic migration.

- We can use `ref` instead of `std::shared_ptr`. The former must be
  initialized (so it is like Rust's `Box` rather than `Option<Box>`,
  This expresses the invariant that the installable are in fact
  initialized much better.

  This is possible because since we just have local variables not
  fields, we can stop worrying about the not-yet-initialized case.

- Fewer lines of code! (Finally I have a large refactor that makes the
  number go down not up...)

- `nix repl` is now implemented in a clearer way.

The last item deserves further mention. `nix repl` is not like the other
installable commands because instead working from once-loaded
installables, it needs to be able to load them again and again.

To properly support this, we make a new superclass
`RawInstallablesCommand`. This class has the argument parsing and
completion logic, but does *not* hand off parsed installables but
instead just the raw string arguments.

This is exactly what `nix repl` needs, and allows us to instead of
having the logic awkwardly split between `prepare`,
`useDefaultInstallables,` and `load`, have everything right next to each
other. I think this will enable future simplifications of that argument
defaulting logic, but I am saving those for a future PR --- best to keep
code motion and more complicated boolean expression rewriting separate
steps.

The "diagnostic ignored `-Woverloaded-virtual`" pragma helps because C++
doesn't like our many `run` methods. In our case, we don't mind the
shadowing it all --- it is *intentional* that the derived class only
provides a `run` method, and doesn't call any of the overridden `run`
methods.

Helps with https://github.com/NixOS/rfcs/pull/134
2023-03-15 16:29:07 -04:00

282 lines
8.4 KiB
C++

#include "run.hh"
#include "command.hh"
#include "common-args.hh"
#include "shared.hh"
#include "store-api.hh"
#include "derivations.hh"
#include "local-store.hh"
#include "finally.hh"
#include "fs-accessor.hh"
#include "progress-bar.hh"
#include "eval.hh"
#include "build/personality.hh"
#if __linux__
#include <sys/mount.h>
#endif
#include <queue>
using namespace nix;
std::string chrootHelperName = "__run_in_chroot";
namespace nix {
void runProgramInStore(ref<Store> store,
const std::string & program,
const Strings & args,
std::optional<std::string_view> system)
{
stopProgressBar();
restoreProcessContext();
/* If this is a diverted store (i.e. its "logical" location
(typically /nix/store) differs from its "physical" location
(e.g. /home/eelco/nix/store), then run the command in a
chroot. For non-root users, this requires running it in new
mount and user namespaces. Unfortunately,
unshare(CLONE_NEWUSER) doesn't work in a multithreaded program
(which "nix" is), so we exec() a single-threaded helper program
(chrootHelper() below) to do the work. */
auto store2 = store.dynamic_pointer_cast<LocalFSStore>();
if (!store2)
throw Error("store '%s' is not a local store so it does not support command execution", store->getUri());
if (store->storeDir != store2->getRealStoreDir()) {
Strings helperArgs = { chrootHelperName, store->storeDir, store2->getRealStoreDir(), std::string(system.value_or("")), program };
for (auto & arg : args) helperArgs.push_back(arg);
execv(getSelfExe().value_or("nix").c_str(), stringsToCharPtrs(helperArgs).data());
throw SysError("could not execute chroot helper");
}
if (system)
setPersonality(*system);
execvp(program.c_str(), stringsToCharPtrs(args).data());
throw SysError("unable to execute '%s'", program);
}
}
struct CmdShell : InstallablesCommand, MixEnvironment
{
using InstallablesCommand::run;
std::vector<std::string> command = { getEnv("SHELL").value_or("bash") };
CmdShell()
{
addFlag({
.longName = "command",
.shortName = 'c',
.description = "Command and arguments to be executed, defaulting to `$SHELL`",
.labels = {"command", "args"},
.handler = {[&](std::vector<std::string> ss) {
if (ss.empty()) throw UsageError("--command requires at least one argument");
command = ss;
}}
});
}
std::string description() override
{
return "run a shell in which the specified packages are available";
}
std::string doc() override
{
return
#include "shell.md"
;
}
void run(ref<Store> store, Installables && installables) override
{
auto outPaths = Installable::toStorePaths(getEvalStore(), store, Realise::Outputs, OperateOn::Output, installables);
auto accessor = store->getFSAccessor();
std::unordered_set<StorePath> done;
std::queue<StorePath> todo;
for (auto & path : outPaths) todo.push(path);
setEnviron();
auto unixPath = tokenizeString<Strings>(getEnv("PATH").value_or(""), ":");
while (!todo.empty()) {
auto path = todo.front();
todo.pop();
if (!done.insert(path).second) continue;
if (true)
unixPath.push_front(store->printStorePath(path) + "/bin");
auto propPath = store->printStorePath(path) + "/nix-support/propagated-user-env-packages";
if (accessor->stat(propPath).type == FSAccessor::tRegular) {
for (auto & p : tokenizeString<Paths>(readFile(propPath)))
todo.push(store->parseStorePath(p));
}
}
setenv("PATH", concatStringsSep(":", unixPath).c_str(), 1);
Strings args;
for (auto & arg : command) args.push_back(arg);
runProgramInStore(store, *command.begin(), args);
}
};
static auto rCmdShell = registerCommand<CmdShell>("shell");
struct CmdRun : InstallableCommand
{
using InstallableCommand::run;
std::vector<std::string> args;
CmdRun()
{
expectArgs({
.label = "args",
.handler = {&args},
.completer = completePath
});
}
std::string description() override
{
return "run a Nix application";
}
std::string doc() override
{
return
#include "run.md"
;
}
Strings getDefaultFlakeAttrPaths() override
{
Strings res{
"apps." + settings.thisSystem.get() + ".default",
"defaultApp." + settings.thisSystem.get(),
};
for (auto & s : SourceExprCommand::getDefaultFlakeAttrPaths())
res.push_back(s);
return res;
}
Strings getDefaultFlakeAttrPathPrefixes() override
{
Strings res{"apps." + settings.thisSystem.get() + "."};
for (auto & s : SourceExprCommand::getDefaultFlakeAttrPathPrefixes())
res.push_back(s);
return res;
}
void run(ref<Store> store, ref<Installable> installable) override
{
auto state = getEvalState();
lockFlags.applyNixConfig = true;
auto app = installable->toApp(*state).resolve(getEvalStore(), store);
Strings allArgs{app.program};
for (auto & i : args) allArgs.push_back(i);
runProgramInStore(store, app.program, allArgs);
}
};
static auto rCmdRun = registerCommand<CmdRun>("run");
void chrootHelper(int argc, char * * argv)
{
int p = 1;
std::string storeDir = argv[p++];
std::string realStoreDir = argv[p++];
std::string system = argv[p++];
std::string cmd = argv[p++];
Strings args;
while (p < argc)
args.push_back(argv[p++]);
#if __linux__
uid_t uid = getuid();
uid_t gid = getgid();
if (unshare(CLONE_NEWUSER | CLONE_NEWNS) == -1)
/* Try with just CLONE_NEWNS in case user namespaces are
specifically disabled. */
if (unshare(CLONE_NEWNS) == -1)
throw SysError("setting up a private mount namespace");
/* Bind-mount realStoreDir on /nix/store. If the latter mount
point doesn't already exists, we have to create a chroot
environment containing the mount point and bind mounts for the
children of /. Would be nice if we could use overlayfs here,
but that doesn't work in a user namespace yet (Ubuntu has a
patch for this:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1478578). */
if (!pathExists(storeDir)) {
// FIXME: Use overlayfs?
Path tmpDir = createTempDir();
createDirs(tmpDir + storeDir);
if (mount(realStoreDir.c_str(), (tmpDir + storeDir).c_str(), "", MS_BIND, 0) == -1)
throw SysError("mounting '%s' on '%s'", realStoreDir, storeDir);
for (auto entry : readDirectory("/")) {
auto src = "/" + entry.name;
Path dst = tmpDir + "/" + entry.name;
if (pathExists(dst)) continue;
auto st = lstat(src);
if (S_ISDIR(st.st_mode)) {
if (mkdir(dst.c_str(), 0700) == -1)
throw SysError("creating directory '%s'", dst);
if (mount(src.c_str(), dst.c_str(), "", MS_BIND | MS_REC, 0) == -1)
throw SysError("mounting '%s' on '%s'", src, dst);
} else if (S_ISLNK(st.st_mode))
createSymlink(readLink(src), dst);
}
char * cwd = getcwd(0, 0);
if (!cwd) throw SysError("getting current directory");
Finally freeCwd([&]() { free(cwd); });
if (chroot(tmpDir.c_str()) == -1)
throw SysError("chrooting into '%s'", tmpDir);
if (chdir(cwd) == -1)
throw SysError("chdir to '%s' in chroot", cwd);
} else
if (mount(realStoreDir.c_str(), storeDir.c_str(), "", MS_BIND, 0) == -1)
throw SysError("mounting '%s' on '%s'", realStoreDir, storeDir);
writeFile("/proc/self/setgroups", "deny");
writeFile("/proc/self/uid_map", fmt("%d %d %d", uid, uid, 1));
writeFile("/proc/self/gid_map", fmt("%d %d %d", gid, gid, 1));
if (system != "")
setPersonality(system);
execvp(cmd.c_str(), stringsToCharPtrs(args).data());
throw SysError("unable to exec '%s'", cmd);
#else
throw Error("mounting the Nix store on '%s' is not supported on this platform", storeDir);
#endif
}