fix(tty): preserve ctty across PTY user close

Keep the Linux pty_close driver callback for the logical last user descriptor, but clear the controlling-session association only on a true final tty release. Add a dunitest that closes the last slave descriptor while the master remains alive and verifies that the session can still reopen /dev/tty with the original SID and foreground process group.

Signed-off-by: longjin <longjin@dragonos.org>

Author: fslongjin

kernel/src/driver/tty/tty_core.rs

@@ -830,15 +830,21 @@ impl TtyOperation for TtyCore {
         let subtype = tty.core().driver().tty_driver_sub_type();
         let is_pty_slave_last = cnt == 1 && subtype == TtyDriverSubType::PtySlave;
         let is_pty_master_last = cnt == 1 && subtype == TtyDriverSubType::PtyMaster;
-        if !self.core().count_valid() || is_pty_slave_last || is_pty_master_last {
+        let final_release = !self.core().count_valid();
+        if final_release || is_pty_slave_last || is_pty_master_last {
             // log::debug!(
             //     "TtyCore close: ref count: {}, tty: {}",
             //     cnt,
             //     tty.core().name()
             // );
             let r = self.core().tty_driver.driver_funcs().close(tty.clone());
-            // 如果计数为0或者无效，表示tty已经关闭
-            let _ = TtyJobCtrlManager::remove_session_tty(&tty);
+            // Linux pty_close() runs when the last user fd closes even though
+            // the peer keeps the tty structure count at one. The controlling
+            // session remains attached in that case and may reopen /dev/tty;
+            // only a true final structure release clears it here.
+            if final_release {
+                let _ = TtyJobCtrlManager::remove_session_tty(&tty);
+            }
             return r;
         }
         Ok(())

user/apps/tests/dunitest/suites/normal/tty_pty_hangup.cc

@@ -632,6 +632,65 @@ TEST(TtyPtyHangup, SlaveCanReopenWhileMasterAliveAfterLastSlaveClose) {
     EXPECT_EQ('r', ch);
 }
 
+TEST(TtyPtyHangup, ControllingSlaveCanReopenDevTtyAfterLastFdClose) {
+    PtyPair pair = OpenRawPty();
+    ASSERT_GE(pair.master.get(), 0);
+    ASSERT_GE(pair.slave.get(), 0);
+
+    int gate[2] = {-1, -1};
+    ASSERT_EQ(0, pipe(gate)) << strerror(errno);
+
+    pid_t child = fork();
+    ASSERT_GE(child, 0) << strerror(errno);
+    if (child == 0) {
+        close(gate[1]);
+        close(pair.master.release());
+        if (setsid() < 0) {
+            _exit(1);
+        }
+        if (ioctl(pair.slave.get(), TIOCSCTTY, 0) < 0) {
+            _exit(2);
+        }
+
+        char token = 0;
+        if (read(gate[0], &token, sizeof(token)) != sizeof(token)) {
+            _exit(3);
+        }
+        close(gate[0]);
+        pair.slave.reset();
+
+        int tty_fd = open("/dev/tty", O_RDWR | O_NOCTTY);
+        if (tty_fd < 0) {
+            _exit(4);
+        }
+        pid_t foreground = tcgetpgrp(tty_fd);
+        pid_t sid = -1;
+        if (foreground != getpgrp() || ioctl(tty_fd, TIOCGSID, &sid) < 0 ||
+            sid != getsid(0)) {
+            close(tty_fd);
+            _exit(5);
+        }
+        close(tty_fd);
+        _exit(0);
+    }
+
+    close(gate[0]);
+    pair.slave.reset();
+    char token = 'R';
+    ssize_t gate_write = -1;
+    do {
+        gate_write = write(gate[1], &token, sizeof(token));
+    } while (gate_write < 0 && errno == EINTR);
+    int gate_errno = errno;
+    close(gate[1]);
+    ASSERT_EQ(static_cast<ssize_t>(sizeof(token)), gate_write) << strerror(gate_errno);
+
+    int status = 0;
+    ASSERT_TRUE(WaitForChild(child, &status));
+    ASSERT_TRUE(WIFEXITED(status)) << "child status=" << status;
+    ASSERT_EQ(0, WEXITSTATUS(status)) << "child status=" << status;
+}
+
 TEST(TtyPtyHangup, ReopenedSlaveKeepsIndexReservedAfterMasterClose) {
     char first_name[128] = {};
     PtyPair pair = OpenRawPty(first_name);