Merge branch 'force-bg'

BUGS

@@ -5,9 +5,3 @@
 - Attaching to a process with children doesn't work right.
   This should be possible to fix -- I just need to ptrace each child
   individually and do the same games to it.
-
-- After attaching to a curses application, the arrow keys may not work
-  right. This is because of terminal state that is configured by
-  sending control characters to the terminal emulator, instead of
-  through termios, and so I can't easily restore. Suspending and
-  resuming the app will often usually perform the appropriate reset.

README

@@ -21,18 +21,6 @@ background it, you will still have to run "bg" or "fg" in the old
 terminal. This is likely impossible to fix in a reasonable way without
 patching your shell.)
 
-After attaching, you may need to send a ^L or similar to ncurses
-applications to force them to redraw themselves. With "less", after
-attaching, a ^Z will cause it to both redraw and to set up the
-terminal application keys so that you can scroll with arrow keys
-again.
-
-After attaching, your old terminal will probably be left in a strange
-state, since it will be waiting for the process to quit, but not
-getting any output. You can either background your process and do 'bg;
-disown', or just close the window -- reptyr should protect your
-process from being killed when you do so.
-
 "But wait, isn't this just screenify?"
 --------------------------------------
 

attach.c

@@ -12,6 +12,8 @@
 #include <sys/wait.h>
 #include <signal.h>
 #include <limits.h>
+#include <time.h>
+#include <sys/time.h>
 
 #include "ptrace.h"
 #include "reptyr.h"
@@ -145,9 +147,9 @@ int do_setsid(struct ptrace_child *child) {
     kill(dummy.pid, SIGKILL);
     ptrace_detach_child(&dummy);
     ptrace_wait(&dummy);
-    ptrace_remote_syscall(child, __NR_waitid,
-                          P_PID, dummy.pid, 0, WNOHANG,
-                          0, 0);
+    ptrace_remote_syscall(child, __NR_wait4,
+                          dummy.pid, 0, WNOHANG,
+                          0, 0, 0);
     return err;
 }
 
@@ -172,6 +174,84 @@ int ignore_hup(struct ptrace_child *child, unsigned long scratch_page) {
     return err;
 }
 
+/*
+ * Wait for the specific pid to enter state 'T', or stopped. We have to pull the
+ * /proc file rather than attaching with ptrace() and doing a wait() because
+ * half the point of this exercise is for the process's real parent (the shell)
+ * to see the TSTP.
+ *
+ * In case the process is masking or ignoring SIGTSTP, we time out after a
+ * second and continue with the attach -- it'll still work mostly right, you
+ * just won't get the old shell back.
+ */
+void wait_for_stop(pid_t pid) {
+    struct timeval start, now;
+    struct timespec sleep;
+    char stat_path[PATH_MAX], buf[256], *p;
+    int fd;
+
+    snprintf(stat_path, sizeof stat_path, "/proc/%d/stat", pid);
+    fd = open(stat_path, O_RDONLY);
+    if (!fd) {
+        error("Unable to open %s: %s", stat_path, strerror(errno));
+        return;
+    }
+    gettimeofday(&start, NULL);
+    while (1) {
+        gettimeofday(&now, NULL);
+        if ((now.tv_sec > start.tv_sec && now.tv_usec > start.tv_usec)
+            || (now.tv_sec - start.tv_sec > 1)) {
+            error("Timed out waiting for child stop.");
+            break;
+        }
+        /*
+         * If anything goes wrong reading or parsing the stat node, just give
+         * up.
+         */
+        lseek(fd, 0, SEEK_SET);
+        if (read(fd, buf, sizeof buf) <= 0)
+            break;
+        p = strchr(buf, ' ');
+        if (!p)
+            break;
+        p = strchr(p+1, ' ');
+        if (!p)
+            break;
+        if (*(p+1) == 'T')
+            break;
+
+        sleep.tv_sec  = 0;
+        sleep.tv_nsec = 10000000;
+        nanosleep(&sleep, NULL);
+    }
+    close(fd);
+}
+
+int copy_tty_state(pid_t pid, const char *pty) {
+    char buf[PATH_MAX];
+    int fd, err = 0;
+    struct termios tio;
+
+    snprintf(buf, sizeof buf, "/proc/%d/fd/0", pid);
+    if ((fd = open(buf, O_RDONLY)) < 0)
+        return -errno;
+
+    if (tcgetattr(fd, &tio) < 0) {
+        err = errno;
+        goto out;
+    }
+    close(fd);
+
+    if ((fd = open(pty, O_RDONLY)) < 0)
+        return -errno;
+
+    if (tcsetattr(fd, TCSANOW, &tio) < 0)
+        err = errno;
+out:
+    close(fd);
+    return -err;
+}
+
 int attach_child(pid_t pid, const char *pty) {
     struct ptrace_child child;
     unsigned long scratch_page = -1;
@@ -180,9 +260,16 @@ int attach_child(pid_t pid, const char *pty) {
     int err = 0;
     long page_size = sysconf(_SC_PAGE_SIZE);
 
+    if ((err = copy_tty_state(pid, pty)) < 0)
+        return -err;
+
+    kill(pid, SIGTSTP);
+    wait_for_stop(pid);
 
-    if (ptrace_attach_child(&child, pid))
+    if (ptrace_attach_child(&child, pid)) {
+        kill(pid, SIGCONT);
         return child.error;
+    }
 
     if (ptrace_advance_to_state(&child, ptrace_at_syscall)) {
         err = child.error;
@@ -227,21 +314,6 @@ int attach_child(pid_t pid, const char *pty) {
 
     debug("Opened the new tty in the child: %d", child_fd);
 
-    err = ptrace_remote_syscall(&child, __NR_ioctl,
-                                child_tty_fds[0], TCGETS, scratch_page,
-                                0, 0, 0);
-    debug("TCGETS(%d): %d", child_tty_fds[0], err);
-    if(err < 0)
-        goto out_close;
-    err = ptrace_remote_syscall(&child, __NR_ioctl,
-                                child_fd, TCSETS, scratch_page,
-                                0, 0, 0);
-    debug("TCSETS: %d", err);
-    if (err < 0)
-        goto out_close;
-
-    debug("Copied terminal settings");
-
     err = ignore_hup(&child, scratch_page);
     if (err < 0)
         goto out_close;
@@ -290,8 +362,10 @@ int attach_child(pid_t pid, const char *pty) {
  out_detach:
     ptrace_detach_child(&child);
 
-    if (err == 0)
+    if (err == 0) {
+        kill(child.pid, SIGCONT);
         kill(child.pid, SIGWINCH);
+    }
 
     return err < 0 ? -err : err;
 }

ptrace.c

@@ -105,10 +105,6 @@ int ptrace_wait(struct ptrace_child *child) {
                 ptrace_command(child, PTRACE_GETEVENTMSG, 0, &child->forked_pid);
             if (child->state != ptrace_at_syscall)
                 child->state = ptrace_stopped;
-            if (sig != SIGSTOP && sig != SIGTRAP && sig != SIGCHLD && sig != SIGHUP && sig != SIGCONT) {
-                child->error = EAGAIN;
-                return -1;
-            }
         }
     } else {
         child->error = EINVAL;
@@ -122,8 +118,12 @@ int ptrace_advance_to_state(struct ptrace_child *child,
     int err;
     while(child->state != desired) {
         switch(desired) {
-        case ptrace_at_syscall:
         case ptrace_after_syscall:
+        case ptrace_at_syscall:
+            if (WIFSTOPPED(child->status) && WSTOPSIG(child->status) == SIGSEGV) {
+                child->error = EAGAIN;
+                return -1;
+            }
             err = ptrace_command(child, PTRACE_SYSCALL, 0, 0);
             break;
         case ptrace_running: