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daemon: use kj for splicing stdio connections

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drop our reimplementation of splice for non-linux in favor of using kj
pumpTo. this avoids select() for its O(maxfd) behavior, and if kj ever
uses something more efficient than read/write loops we'll benefit too.

Change-Id: Id01ba84bf8831455af2d9755bf1a3039d215bb47
This commit is contained in:
eldritch horrors
2025-07-22 10:39:32 +00:00
parent bf3d52e5bb
commit d8dfffbe37
2 changed files with 18 additions and 48 deletions
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lix/nix/daemon.cc
+15 -48
View File
@@ -81,27 +81,6 @@ AuthorizationSettings authorizationSettings;
static GlobalConfig::Register rSettings(&authorizationSettings);
#ifndef __linux__
#define SPLICE_F_MOVE 0
static ssize_t splice(int fd_in, void *off_in, int fd_out, void *off_out, size_t len, unsigned int flags)
{
// We ignore most parameters, we just have them for conformance with the linux syscall
std::vector<char> buf(8192);
auto read_count = read(fd_in, buf.data(), buf.size());
if (read_count == -1)
return read_count;
auto write_count = decltype(read_count)(0);
while (write_count < read_count) {
auto res = write(fd_out, buf.data() + write_count, read_count - write_count);
if (res == -1)
return res;
write_count += res;
}
return read_count;
}
#endif
static void sigChldHandler(int sigNo)
{
// Ensure we don't modify errno of whatever we've interrupted
@@ -470,34 +449,22 @@ static void daemonInstance(AsyncIoRoot & aio, std::optional<TrustedFlag> forceTr
*
* Loops until standard input disconnects, or an error is encountered.
*/
static void forwardStdioConnection(RemoteStore & store) {
static void forwardStdioConnection(AsyncIoRoot & aio, RemoteStore & store)
{
auto conn = store.openConnectionWrapper();
int from = conn->getFD();
int to = conn->getFD();
auto connSocket = AIO().lowLevelProvider.wrapSocketFd(conn->getFD());
auto stdin = AIO().lowLevelProvider.wrapInputFd(STDIN_FILENO);
auto stdout = AIO().lowLevelProvider.wrapOutputFd(STDOUT_FILENO);
auto nfds = std::max(from, STDIN_FILENO) + 1;
while (true) {
fd_set fds;
FD_ZERO(&fds);
FD_SET(from, &fds);
FD_SET(STDIN_FILENO, &fds);
if (select(nfds, &fds, nullptr, nullptr, nullptr) == -1)
throw SysError("waiting for data from client or server");
if (FD_ISSET(from, &fds)) {
auto res = splice(from, nullptr, STDOUT_FILENO, nullptr, SSIZE_MAX, SPLICE_F_MOVE);
if (res == -1)
throw SysError("splicing data from daemon socket to stdout");
else if (res == 0)
throw EndOfFile("unexpected EOF from daemon socket");
}
if (FD_ISSET(STDIN_FILENO, &fds)) {
auto res = splice(STDIN_FILENO, nullptr, to, nullptr, SSIZE_MAX, SPLICE_F_MOVE);
if (res == -1)
throw SysError("splicing data from stdin to daemon socket");
else if (res == 0)
return;
}
}
aio.blockOn(connSocket->pumpTo(*stdout)
.then([](auto) -> Result<void> {
return {
std::make_exception_ptr(EndOfFile("unexpected EOF from daemon socket"))
};
})
.exclusiveJoin(stdin->pumpTo(*connSocket).then([](auto) -> Result<void> {
return result::success();
})));
}
/**
@@ -534,7 +501,7 @@ runDaemon(AsyncIoRoot & aio, bool stdio, std::optional<TrustedFlag> forceTrustCl
// must process it ourselves (before delegating to the next store) to
// force untrusting the client.
if (auto remoteStore = store.try_cast_shared<RemoteStore>(); remoteStore && (!forceTrustClientOpt || *forceTrustClientOpt != NotTrusted))
forwardStdioConnection(*remoteStore);
forwardStdioConnection(aio, *remoteStore);
else
// `Trusted` is passed in the auto (no override case) because we
// cannot see who is on the other side of a plain pipe. Limiting
tests/functional/remote-store.sh
+3
View File
@@ -31,4 +31,7 @@ nix-store --dump-db > $TEST_ROOT/d1
NIX_REMOTE= nix-store --dump-db > $TEST_ROOT/d2
cmp $TEST_ROOT/d1 $TEST_ROOT/d2
# check that proxying one daemon through another works
nix --store 'ssh-ng://localhost?remote-store=ssh-ng%3a%2f%2flocalhost' store add-file ./ifd.nix
killDaemon