1 files changed, 255 insertions, 0 deletions

diff --git a/tools/libxl/libxl_fork.c b/tools/libxl/libxl_fork.c
index dce88ad54b..35c8bdd7f3 100644
--- a/tools/libxl/libxl_fork.c
+++ b/tools/libxl/libxl_fork.c
@@ -46,6 +46,12 @@ static int atfork_registered;
 static LIBXL_LIST_HEAD(, libxl__carefd) carefds =
     LIBXL_LIST_HEAD_INITIALIZER(carefds);
 
+/* non-null iff installed, protected by no_forking */
+static libxl_ctx *sigchld_owner;
+static struct sigaction sigchld_saved_action;
+
+static void sigchld_removehandler_core(void);
+
 static void atfork_lock(void)
 {
     int r = pthread_mutex_lock(&no_forking);
@@ -107,6 +113,7 @@ void libxl_postfork_child_noexec(libxl_ctx *ctx)
     int r;
 
     atfork_lock();
+
     LIBXL_LIST_FOREACH_SAFE(cf, &carefds, entry, cf_tmp) {
         if (cf->fd >= 0) {
             r = close(cf->fd);
@@ -118,6 +125,10 @@ void libxl_postfork_child_noexec(libxl_ctx *ctx)
         free(cf);
     }
     LIBXL_LIST_INIT(&carefds);
+
+    if (sigchld_owner)
+        sigchld_removehandler_core();
+
     atfork_unlock();
 }
 
@@ -141,6 +152,250 @@ int libxl__carefd_fd(const libxl__carefd *cf)
 }
 
 /*
+ * Actual child process handling
+ */
+
+static void sigchld_handler(int signo)
+{
+    int e = libxl__self_pipe_wakeup(sigchld_owner->sigchld_selfpipe[1]);
+    assert(!e); /* errors are probably EBADF, very bad */
+}
+
+static void sigchld_removehandler_core(void)
+{
+    struct sigaction was;
+    int r;
+    
+    r = sigaction(SIGCHLD, &sigchld_saved_action, &was);
+    assert(!r);
+    assert(!(was.sa_flags & SA_SIGINFO));
+    assert(was.sa_handler == sigchld_handler);
+    sigchld_owner = 0;
+}
+
+void libxl__sigchld_removehandler(libxl_ctx *ctx) /* non-reentrant */
+{
+    atfork_lock();
+    if (sigchld_owner == ctx)
+        sigchld_removehandler_core();
+    atfork_unlock();
+}
+
+int libxl__sigchld_installhandler(libxl_ctx *ctx) /* non-reentrant */
+{
+    int r, rc;
+
+    if (ctx->sigchld_selfpipe[0] < 0) {
+        r = pipe(ctx->sigchld_selfpipe);
+        if (r) {
+            ctx->sigchld_selfpipe[0] = -1;
+            LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR,
+                             "failed to create sigchld pipe");
+            rc = ERROR_FAIL;
+            goto out;
+        }
+    }
+
+    atfork_lock();
+    if (sigchld_owner != ctx) {
+        struct sigaction ours;
+
+        assert(!sigchld_owner);
+        sigchld_owner = ctx;
+
+        memset(&ours,0,sizeof(ours));
+        ours.sa_handler = sigchld_handler;
+        sigemptyset(&ours.sa_mask);
+        ours.sa_flags = SA_NOCLDSTOP | SA_RESTART;
+        r = sigaction(SIGCHLD, &ours, &sigchld_saved_action);
+        assert(!r);
+
+        assert(((void)"application must negotiate with libxl about SIGCHLD",
+                !(sigchld_saved_action.sa_flags & SA_SIGINFO) &&
+                (sigchld_saved_action.sa_handler == SIG_DFL ||
+                 sigchld_saved_action.sa_handler == SIG_IGN)));
+    }
+    atfork_unlock();
+
+    rc = 0;
+ out:
+    return rc;
+}
+
+static int chldmode_ours(libxl_ctx *ctx)
+{
+    return ctx->childproc_hooks->chldowner == libxl_sigchld_owner_libxl;
+}
+
+int libxl__fork_selfpipe_active(libxl_ctx *ctx)
+{
+    /* Returns the fd to read, or -1 */
+    if (!chldmode_ours(ctx))
+        return -1;
+
+    if (LIBXL_LIST_EMPTY(&ctx->children))
+        return -1;
+
+    return ctx->sigchld_selfpipe[0];
+}
+
+static void perhaps_removehandler(libxl_ctx *ctx)
+{
+    if (LIBXL_LIST_EMPTY(&ctx->children) &&
+        ctx->childproc_hooks->chldowner != libxl_sigchld_owner_libxl_always)
+        libxl__sigchld_removehandler(ctx);
+}
+
+static int childproc_reaped(libxl__egc *egc, pid_t pid, int status)
+{
+    EGC_GC;
+    libxl__ev_child *ch;
+
+    LIBXL_LIST_FOREACH(ch, &CTX->children, entry)
+        if (ch->pid == pid)
+            goto found;
+
+    /* not found */
+    return ERROR_UNKNOWN_CHILD;
+
+ found:
+    LIBXL_LIST_REMOVE(ch, entry);
+    ch->pid = -1;
+    ch->callback(egc, ch, pid, status);
+
+    perhaps_removehandler(CTX);
+
+    return 0;
+}
+
+int libxl_childproc_reaped(libxl_ctx *ctx, pid_t pid, int status)
+{
+    EGC_INIT(ctx);
+    CTX_LOCK;
+    int rc = childproc_reaped(egc, pid, status);
+    CTX_UNLOCK;
+    EGC_FREE;
+    return rc;
+}
+
+void libxl__fork_selfpipe_woken(libxl__egc *egc)
+{
+    /* May make callbacks into the application for child processes.
+     * ctx must be locked EXACTLY ONCE */
+    EGC_GC;
+
+    while (chldmode_ours(CTX) /* in case the app changes the mode */) {
+        int status;
+        pid_t pid = waitpid(-1, &status, WNOHANG);
+
+        if (pid == 0) return;
+
+        if (pid == -1) {
+            if (errno == ECHILD) return;
+            if (errno == EINTR) continue;
+            LIBXL__EVENT_DISASTER(egc, "waitpid() failed", errno, 0);
+            return;
+        }
+
+        int rc = childproc_reaped(egc, pid, status);
+
+        if (rc) {
+            if (CTX->childproc_hooks->reaped_callback) {
+                CTX_UNLOCK;
+                rc = CTX->childproc_hooks->reaped_callback
+                        (pid, status, CTX->childproc_user);
+                CTX_LOCK;
+                if (rc != 0 && rc != ERROR_UNKNOWN_CHILD) {
+                    char disasterbuf[200];
+                    snprintf(disasterbuf, sizeof(disasterbuf), " reported by"
+                             " libxl_childproc_hooks->reaped_callback"
+                             " (for pid=%lu, status=%d; error code %d)",
+                             (unsigned long)pid, status, rc);
+                    LIBXL__EVENT_DISASTER(egc, disasterbuf, 0, 0);
+                    return;
+                }
+            } else {
+                rc = ERROR_UNKNOWN_CHILD;
+            }
+            if (rc)
+                libxl_report_child_exitstatus(CTX, XTL_WARN,
+                                "unknown child", (long)pid, status);
+        }
+    }
+}
+
+pid_t libxl__ev_child_fork(libxl__gc *gc, libxl__ev_child *ch,
+                           libxl__ev_child_callback *death)
+{
+    CTX_LOCK;
+    int rc;
+
+    if (chldmode_ours(CTX)) {
+        rc = libxl__sigchld_installhandler(CTX);
+        if (rc) goto out;
+    }
+
+    pid_t pid =
+        CTX->childproc_hooks->fork_replacement
+        ? CTX->childproc_hooks->fork_replacement(CTX->childproc_user)
+        : fork();
+    if (pid == -1) {
+        LOGE(ERROR, "fork failed");
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    if (!pid) {
+        /* woohoo! */
+        return 0; /* Yes, CTX is left locked in the child. */
+    }
+
+    ch->pid = pid;
+    ch->callback = death;
+    LIBXL_LIST_INSERT_HEAD(&CTX->children, ch, entry);
+    rc = pid;
+
+ out:
+    perhaps_removehandler(CTX);
+    CTX_UNLOCK;
+    return rc;
+}
+
+void libxl_childproc_setmode(libxl_ctx *ctx, const libxl_childproc_hooks *hooks,
+                             void *user)
+{
+    GC_INIT(ctx);
+    CTX_LOCK;
+
+    assert(LIBXL_LIST_EMPTY(&CTX->children));
+
+    if (!hooks)
+        hooks = &libxl__childproc_default_hooks;
+
+    ctx->childproc_hooks = hooks;
+    ctx->childproc_user = user;
+
+    switch (ctx->childproc_hooks->chldowner) {
+    case libxl_sigchld_owner_mainloop:
+    case libxl_sigchld_owner_libxl:
+        libxl__sigchld_removehandler(ctx);
+        break;
+    case libxl_sigchld_owner_libxl_always:
+        libxl__sigchld_installhandler(ctx);
+        break;
+    default:
+        abort();
+    }
+
+    CTX_UNLOCK;
+    GC_FREE;
+}
+
+const libxl_childproc_hooks libxl__childproc_default_hooks = {
+    libxl_sigchld_owner_libxl, 0, 0
+};
+
+/*
  * Local variables:
  * mode: C
  * c-basic-offset: 4