daemon: Phase 0 platform seams (ADR 0020) — eventfd/SO_PEERCRED/instance-lock/XDG behind platform/, zero behaviour change

Introduces the four rpc-layer seams docs/08-porting.md calls for this lane: platform::Wakeup (eventfd), platform::peer_of (SO_PEERCRED/struct ucred, same-UID check preserved unchanged), platform::acquire_instance_lock (abstract-namespace socket), platform::runtime_base_dir/data_base_dir (XDG lookups). Today's Linux code moves unchanged into daemon/src/rpc/platform/linux/; the seam headers carry no OS types and no #ifdef. No fifth interface for timerfd: EventLoop gains a portable add_timer() that folds the next deadline into poll()'s own timeout, replacing both timerfd instances in main.cpp — the loop already computes a deadline, so this needs no per-OS backend at all. Full suite 59/59 green; no #ifdef outside platform/linux/, no behaviour change. Co-Authored-By: Claude Sonnet 5 <[email protected]>
2026-09-15 17:54:32 +04:00
parent 4e87730ce9
commit 6d7c4f7bc4
17 changed files with 321 additions and 143 deletions
@@ -0,0 +1,38 @@
+#include "rpc/platform/instance_lock.hpp"
+
+#include <cstddef>
+#include <cstring>
+
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+#include "util/crypto.hpp"
+
+namespace velox::daemon::rpc::platform {
+
+int acquire_instance_lock(const std::string& runtime_dir) {
+    const int fd = ::socket(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0);
+    if (fd < 0) return -1;
+
+    // Truncated to 16 hex chars (64 bits): a collision would need two distinct runtime
+    // dirs to hash together, which is not a security boundary here — the socket itself is
+    // still 0600 same-UID-checked; this is only "don't let two daemons stomp each other".
+    const std::string name =
+        "velox-daemon-" + velox::daemon::crypto::sha256_hex(runtime_dir).substr(0, 16);
+    sockaddr_un addr{};
+    addr.sun_family = AF_UNIX;
+    // Leading NUL selects the abstract namespace; the name follows, not NUL-terminated.
+    addr.sun_path[0] = '\0';
+    std::memcpy(addr.sun_path + 1, name.c_str(), name.size());
+    const socklen_t len =
+        static_cast<socklen_t>(offsetof(sockaddr_un, sun_path) + 1 + name.size());
+
+    if (::bind(fd, reinterpret_cast<sockaddr*>(&addr), len) != 0) {
+        ::close(fd);
+        return -1;
+    }
+    return fd;
+}
+
+}  // namespace velox::daemon::rpc::platform