Introduce signals module for signal handling

src/root.zig

@@ -5,8 +5,10 @@ pub const deps = struct {
 
 pub const config  = @import("config/config.zig");
 pub const memory  = @import("memory/util.zig");
+pub const signals = @import("signals/models.zig");
 
 test {
     _ = config;
     _ = memory;
+    _ = signals;
 }

src/signals/models.zig

@@ -0,0 +1,53 @@
+const std   = @import("std");
+const posix = std.posix;
+const linux = std.os.linux;
+
+pub const Event = enum {
+    none,     // Sentinel
+    shutdown, // SIGTERM, SIGINT
+    reload,   // SIGHUP
+
+    pub fn fromSignal(sig: i32) ?Event
+    {
+        const signal: posix.SIG = @enumFromInt(@as(u32, @intCast(sig)));
+
+        return switch (signal) {
+            .TERM,
+            .INT   => .shutdown,
+            .HUP   => .reload,
+            else   => null,
+        };
+    }
+};
+
+pub const SignalFd = struct {
+    fd: posix.fd_t,
+
+    pub fn init() !SignalFd
+    {
+        var mask = linux.sigemptyset();
+
+        linux.sigaddset(&mask, posix.SIG.TERM);
+        linux.sigaddset(&mask, posix.SIG.INT);
+        linux.sigaddset(&mask, posix.SIG.HUP);
+
+        posix.sigprocmask(posix.SIG.BLOCK, &mask, null);
+
+        const fd = try posix.signalfd(-1, &mask, linux.SFD.CLOEXEC);
+
+        return .{ .fd = fd };
+    }
+
+    pub fn deinit(self: SignalFd) void { _ = std.os.linux.close(self.fd); }
+
+    //
+
+    pub fn read(self: SignalFd) !Event
+    {
+        var info: linux.signalfd_siginfo = undefined;
+
+        _ = try posix.read(self.fd, std.mem.asBytes(&info));
+
+        return Event.fromSignal(@intCast(info.signo)) orelse .none;
+    }
+};