X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?a=blobdiff_plain;f=cprogs%2Fcgi-fcgi-interp.c;h=63db94b35fed7a1d3afb3f11c96858a31d3c70d7;hb=HEAD;hp=9df31034aa8da607297ea67dff618b86c5c5e755;hpb=71eaa17c0ac8118db72b3ba7a24ad45345608694;p=chiark-utils.git

diff --git a/cprogs/cgi-fcgi-interp.c b/cprogs/cgi-fcgi-interp.c
index 9df3103..6ea886e 100644
--- a/cprogs/cgi-fcgi-interp.c
+++ b/cprogs/cgi-fcgi-interp.c
@@ -1,12 +1,17 @@
 /*
  * "Interpreter" that you can put in #! like this
  *   #!/usr/bin/cgi-fcgi-interp [<options>] <interpreter>
- *   #!/usr/bin/cgi-fcgi-interp [<options>],<interpreter>
+ *
+ * Usages:
+ *   cgi-fcgi-interp  [<option> ..] <interpreter>  <script> [<ignored> ...]
+ *   cgi-fcgi-interp  [<option>,..],<interpreter>  <script> [<ignored> ...]
+ *   cgi-fcgi-interp '[<option> ..] <interpreter>' <script> [<ignored> ...]
  */
 /*
- * cgi-fcgi-interp.[ch] - C helpers common to the whole of chiark-utils
+ * cgi-fcgi-interp.[ch] - Convenience wrapper for cgi-fcgi
  *
  * Copyright 2016 Ian Jackson
+ * Copyright 1982,1986,1993 The Regents of the University of California
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -22,6 +27,8 @@
  * License along with this file; if not, consult the Free Software
  * Foundation's website at www.fsf.org, or the GNU Project website at
  * www.gnu.org.
+ *
+ * See below for a BSD 3-clause notice regarding timespeccmp.
  */
 /*
  * The result is a program which looks, when executed via the #!
@@ -34,8 +41,18 @@
  *          The real interpreter to use.  Eg "perl".  Need not
  *          be an absolute path; will be fed to execvp.
  *
+ *  -G<ident-info>
+ *          Add <ident-info> to the unique identifying information for
+ *          this fcgi program.  May be repeated; order is significant.
+ *
+ *  -E<ident-info-env-var>
+ *          Look <ident-info-env-var> up in the environment and add
+ *          <ident-info-env-var>=<value> as if specified with -G.  If
+ *          the variable is unset in the environment, it is as if
+ *          -G<ident-info-env-var> was specified.
+ *
  *  -g<ident>
- *          Use <ident> rather than hex(sha256(<script>))
+ *          Use <ident> rather than hex(sha256(<interp>\0<script>\0))
  *          as the basename of the leafname of the fcgi rendezvous
  *          socket.  If <ident> contains only hex digit characters it
  *          ought to be no more than 32 characters.  <ident> should
@@ -47,6 +64,14 @@
  *         speedy, the specified number of servers is started
  *         right away.)  The default is 4.
  *
+ *  -c<interval>
+ *         Stale server check interval, in seconds.  The worker
+ *         process group will get a SIGTERM when it is no longer
+ *         needed to process new requests.  Ideally it would continue
+ *         to serve any existing requests.  The SIGTERM will arrive no
+ *         earlier than <interval> after the last request arrived at
+ *         the containing webserver.  Default is 300.
+ *
  *  -D
  *         Debug mode.  Do not actually run program.  Instead, print
  *         out what we would do.
@@ -58,17 +83,16 @@
  * cgi-fcgi-interp automatically expires old sockets, including
  * ones where the named script is out of date.
  */
-
 /*
  * Uses one of two directories
  *   /var/run/user/<UID>/cgi-fcgi-interp/
  *   ~/.cgi-fcgi-interp/<node>/
  * and inside there uses these paths
  *   s<ident>
- *   g<inum>
+ *   l<ident>    used to lock around garbage collection
  *
- * If -M<ident> is not specified then an initial substricg of the
- * lowercase hex of the sha256 of the <script> (ie, our argv[1]) is
+ * If -M<ident> is not specified then an initial substring of the
+ * lowercase hex of the sha256 of <interp>\0<script>\0 is
  * used.  The substring is chosen so that the whole path is 10 bytes
  * shorter than sizeof(sun_path).  But always at least 33 characters.
  *
@@ -87,257 +111,438 @@
  *  - check for and maybe create <base>
  *  - stat and lstat the <script>
  *  - stat the socket and check its timestamp
- *       if it is too hold, rename it to g<inum> (where
- *       <inum> is in decimal)
- *       and run garbage collection
- *  - run  cgi-fcgi -connect SOCKET SCRIPT
+ *       if it is too old, unlink it
+ *  - dup stderr, mark no cloexec
+ *  - set CHIARKUTILS_CGIFCGIINTERP_STAGE2=<stderr-copy-fd>
+ *  - run     cgi-fcgi -connect SOCKET <script>
+ *
+ * When CHIARKUTILS_CGIFCGIINTERP_STAGE2 is set, --stage2 does this:
+ *  - dup2 <was-stderr> to fd 2
+ *  - open /dev/null and expect fd 1 (and if not, close it)
+ *  - become a new process group
+ *  - lstat <socket> to find its inum, mtime
+ *  - fork/exec <interp> <script>
+ *  - periodically lstat <interp> and <script> and
+ *      if mtime is newer than our start time
+ *      kill process group (at second iteration)
  */
 
-#include "common.h"
+#include "prefork.h"
+#include "timespeccmp.h"
 
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <errno.h>
-#include <stdbool.h>
-#include <assert.h>
-#include <limits.h>
+#define STAGE2_VAR "CHIARKUTILS_CGIFCGIINTERP_STAGE2"
 
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <sys/utsname.h>
-#include <sys/socket.h>
-#include <sys/un.h>
-#include <unistd.h>
-#include <pwd.h>
-#include <err.h>
+static const char *stage2;
 
-#include <nettle/sha.h>
+const char our_name[] = "cgi-fcgi-interp";
 
-#include "myopt.h"
+static int numservers=4, debugmode;
+static int check_interval=300;
 
-#define die  common_die
-#define diee common_diee
+const struct cmdinfo cmdinfos[]= {
+  PREFORK_CMDINFOS
+  { 0, 'M',   1, .call=of_iassign,  .iassignto= &numservers            },
+  { 0, 'D',   0,                    .iassignto= &debugmode,    .arg= 1 },
+  { 0, 'c',   1, .call=of_iassign,  .iassignto= &check_interval        },
+  { 0 }
+};
 
-#define MINHEXHASH 33
+void fusagemessage(FILE *f) {
+  fprintf(f, "usage: #!/usr/bin/cgi-fcgi-interp [<options>]\n");
+}
 
-static const char *interp, *ident;
-static int numservers, debugmode;
+void ident_addinit(void) {
+}
 
-void diee(const char *m) {
-  err(127, "error: %s failed", m);
+static int stderr_copy;
+
+static void make_stderr_copy(void) {
+  stderr_copy = dup(2);
+  if (stderr_copy < 0) diee("dup stderr (for copy for stage2)");
 }
 
-static void fusagemessage(FILE *f) {
-  fprintf(f, "usage: #!/usr/bin/cgi-fcgi-interp [<options>]\n");
+static void prep_stage2(void) {
+  int r;
+  
+  const char *stage2_val = m_asprintf("%d", stderr_copy);
+  r = setenv(STAGE2_VAR, stage2_val, 1);
+  if (r) diee("set %s (to announce to stage2)", STAGE2_VAR);
 }
 
-void usagemessage(void) { fusagemessage(stderr); }
+#ifdef st_mtime
 
-static void of_help(const struct cmdinfo *ci, const char *val) {
-  fusagemessage(stdout);
-  if (ferror(stdout)) diee("write usage message to stdout");
-  exit(0);
+static bool stab_isnewer(const struct stat *a, const struct stat *b) {
+  if (debugmode)
+    fprintf(stderr,"stab_isnewer mtim %lu.%06lu %lu.06%lu\n",
+	    (unsigned long)a->st_mtim.tv_sec,
+	    (unsigned long)a->st_mtim.tv_nsec,
+	    (unsigned long)b->st_mtim.tv_sec,
+	    (unsigned long)b->st_mtim.tv_nsec);
+  return timespeccmp(&a->st_mtim, &b->st_mtim, >);
 }
 
-static void of_iassign(const struct cmdinfo *ci, const char *val) {
-  long v;
-  char *ep;
-  errno= 0; v= strtol(val,&ep,10);
-  if (!*val || *ep || errno || v<INT_MIN || v>INT_MAX)
-    badusage("bad integer argument `%s' for --%s",val,ci->olong);
-  *ci->iassignto = v;
+static void stab_mtimenow(struct stat *out) {
+  int r = clock_gettime(CLOCK_REALTIME, &out->st_mtim);
+  if (r) diee("(stage2) clock_gettime");
+  if (debugmode)
+    fprintf(stderr,"stab_mtimenow mtim %lu.%06lu\n",
+	    (unsigned long)out->st_mtim.tv_sec,
+	    (unsigned long)out->st_mtim.tv_nsec);
 }
 
-#define MAX_OPTS 5
+#else /* !defined(st_mtime) */
 
-static const struct cmdinfo cmdinfos[]= {
-  { "help",   0, .call= of_help               },
-  { 0, 'g',   1, .sassignto= &ident           },
-  { 0, 'M',   1, .call=of_iassign, .iassignto= &numservers      },
-  { 0, 'D',   0, .iassignto= &debugmode, .arg= 1 },
-  { 0 }
-};
+static bool stab_isnewer(const struct stat *a, const struct stat *b) {
+  if (debugmode)
+    fprintf(stderr,"stab_isnewer mtime %lu %lu\n",
+	    (unsigned long)a->st_mtime,
+	    (unsigned long)b->st_mtime);
+  return a->st_mtime > b->st_mtime;
+}
 
-static uid_t us;
-static const char *run_base, *script, *socket_path;
+static void stab_mtimenow(struct stat *out) {
+  out->st_mtime = time(NULL);
+  if (out->st_mtime == (time_t)-1) diee("(stage2) time()");
+  if (debugmode)
+    fprintf(stderr,"stab_mtimenow mtime %lu\n",
+	    (unsigned long)out->st_mtime);
+}
+
+#endif /* !defined(st_mtime) */
 
-static bool find_run_base_var_run(void) {
-  struct stat stab;
-  char *try;
+static bool check_garbage_vs(const struct stat *started) {
+  struct stat script_stab;
   int r;
 
-  try = m_asprintf("%s/%lu", "/var/run/user", us);
-  r = lstat(try, &stab);
-  if (r<0) {
-    if (errno == ENOENT ||
-	errno == ENOTDIR ||
-	errno == EACCES ||
-	errno == EPERM)
-      return 0; /* oh well */
-    diee("stat /var/run/user/UID");
-  }
-  if (!S_ISDIR(stab.st_mode)) {
-    warnx("%s not a directory, falling back to ~\n", try);
-    return 0;
-  }
-  if (stab.st_uid != us) {
-    warnx("%s not owned by uid %lu, falling back to ~\n", try,
-	  (unsigned long)us);
-    return 0;
+  r = lstat(script, &script_stab);
+  if (r) diee("lstat script (%s)",script);
+
+  if (stab_isnewer(&script_stab, started))
+    return 1;
+
+  if (S_ISLNK(script_stab.st_mode)) {
+    r = stat(script, &script_stab);
+    if (r) diee("stat script (%s0",script);
+
+    if (stab_isnewer(&script_stab, started))
+      return 1;
   }
-  if (stab.st_mode & 0077) {
-    warnx("%s writeable by group or other, falling back to ~\n", try);
-    return 0;
+
+  return 0;
+}
+
+static bool check_garbage(void) {
+  struct stat sock_stab;
+  int r;
+
+  r = lstat(socket_path, &sock_stab);
+  if (r) {
+    if ((errno == ENOENT))
+      return 0; /* well, no garbage then */
+    diee("stat socket (%s)",socket_path);
   }
-  run_base = m_asprintf("%s/%s", try, "cgi-fcgi-interp");
-  return 1;
+
+  return check_garbage_vs(&sock_stab);
 }
 
-static bool find_run_base_home(void) {
-  struct passwd *pw;
-  struct utsname ut;
-  char *dot, *try;
+static void tidy_garbage(void) {
+  /* We lock l<ident> and re-check.  The effect of this is that each
+   * stale socket is removed only once.  So unless multiple updates to
+   * the script happen rapidly, we can't be racing with the cgi-fcgi
+   * (which is recreating the socket */
+  int lockfd = -1;
   int r;
 
-  pw = getpwuid(us);  if (!pw) diee("getpwent(uid)");
+  lockfd = acquire_lock();
 
-  r = uname(&ut);   if (r) diee("uname(2)");
-  dot = strchr(ut.nodename, '.');
-  if (dot) *dot = 0;
-  if (sizeof(ut.nodename) > 32)
-    ut.nodename[32] = 0;
+  if (check_garbage()) {
+    r = unlink(socket_path);
+    if (r) {
+      if (!(errno == ENOENT))
+	diee("remove out-of-date socket (%s)", socket_path);
+    }
+  }
 
-  try = m_asprintf("%s/%s/%s", pw->pw_dir, ".cgi-fcgi-interp", ut.nodename);
-  run_base = try;
-  return 1;
+  r = close(lockfd);
+  if (r) diee("close lock (%s)", lock_path);
 }
 
-static void find_socket_path(void) {
-  struct sockaddr_un sun;
+/* stage2 predeclarations */
+static void record_baseline_time(void);
+static void become_pgrp(void);
+static void setup_handlers(void);
+static void spawn_script(void);
+static void queue_alarm(void);
+static void start_logging(void);
+static void await_something(void);
+
+int main(int unused_argc, const char *const *argv) {
   int r;
 
-  us = getuid();  if (us==(uid_t)-1) diee("getuid");
+  stage2 = getenv(STAGE2_VAR);
+  if (stage2) {
+    int stderrfd = atoi(stage2);
+    assert(stderrfd>2);
 
-  find_run_base_var_run() ||
-    find_run_base_home() ||
-    (abort(),0);
+    r = dup2(stderrfd, 2);
+    assert(r==2);
 
-  int maxidentlen = sizeof(sun.sun_path) - strlen(run_base) - 10 - 2;
+    r = open("/dev/null",O_WRONLY);
+    if (r<0) diee("open /dev/null as stdout");
+    if (r>=3) close(r);
+    else if (r!=1) die("open /dev/null for stdout gave bad fd %d",r);
 
-  if (!ident) {
-    if (maxidentlen < MINHEXHASH)
-      errx(127,"base directory `%s'"
-	   " leaves only %d characters for id hash"
-	   " which is too little (<%d)",
-	   run_base, maxidentlen, MINHEXHASH);
+    r = close(stderrfd);
+    if (r) diee("close saved stderr fd");
+  }
 
-    int identlen = maxidentlen > 64 ? 64 : maxidentlen;
-    char *hexident = xmalloc(identlen + 2);
-    struct sha256_ctx sc;
-    unsigned char bbuf[32];
-    int i;
+  process_opts(&argv);
+  if (!script) badusage("need script argument");
 
-    sha256_init(&sc);
-    sha256_update(&sc,strlen(interp)+1,interp);
-    sha256_update(&sc,strlen(script)+1,script);
-    sha256_digest(&sc,sizeof(bbuf),bbuf);
+  if (!stage2) {
+    
+    find_socket_path();
 
-    for (i=0; i<identlen; i += 2)
-      sprintf(hexident+i, "%02x", bbuf[i/2]);
+    bool isgarbage = check_garbage();
 
-    hexident[identlen] = 0;
-    ident = hexident;
-  }
+    if (debugmode) {
+      printf("socket: %s\n",socket_path);
+      printf("interp: %s\n",interp);
+      printf("script: %s\n",script);
+      printf("garbage: %d\n",isgarbage);
+      exit(0);
+    }
 
-  if (strlen(ident) > maxidentlen)
-    errx(127, "base directory `%s' plus ident `%s' too long"
-	 " (with spare) for socket (max ident %d)\n",
-	 run_base, ident, maxidentlen);
+    if (isgarbage)
+      tidy_garbage();
+
+    make_stderr_copy();
+    prep_stage2();
+
+    execlp("cgi-fcgi",
+	   "cgi-fcgi", "-connect", socket_path,
+	   script,
+	   m_asprintf("%d", numservers),
+	   (char*)0);
+    diee("exec cgi-fcgi");
+    
+  } else { /*stage2*/
+
+    record_baseline_time();
+    become_pgrp();
+    setup_handlers();
+    spawn_script();
+    queue_alarm();
+    start_logging();
+    await_something();
+    abort();
 
-  r = mkdir(run_base, 0700);
-  if (r) {
-    if (!(errno == EEXIST))
-      err(127,"mkdir %s",run_base);
   }
+}
 
-  socket_path = m_asprintf("%s/g%s",run_base,ident);
-}  
+/* stage2 */
 
-static bool check_garbage(void) {
-  struct stat sock_stab, cmd_stab;
+/* It is most convenient to handle the recheck timeout, as well as
+ * child death, in signal handlers.  Our signals all block each other,
+ * and the main program has signals blocked except in sigsuspend, so
+ * we don't need to worry about async-signal-safety, or errno. */
+
+static struct stat baseline_time;
+static pid_t script_child, stage2_pgrp;
+static bool out_of_date;
+static int errpipe;
+
+static void record_baseline_time(void) {
+  stab_mtimenow(&baseline_time);
+}
+
+static void become_pgrp(void) {
   int r;
 
-  r = lstat(socket_path, &sock_stab);
-  if (r) {
-    if ((errno == ENOENT))
-      return 0; /* well, no garbage then */
-    err(127,"stat socket (%s)",socket_path);
-  }
+  stage2_pgrp = getpid();
 
-  r = lstat(script, &cmd_stab);
-  if (r) err(127,"lstat script (%s)",script);
+  r = setpgid(0,0);
+  if (r) diee("(stage2) setpgid");
+}
 
-  return 0;
+static void atexit_handler(void) {
+  int r;
+
+  sighandler_t sigr = signal(SIGTERM,SIG_IGN);
+  if (sigr == SIG_ERR) warninge("(stage2) signal(SIGTERM,SIG_IGN)");
+
+  r = killpg(stage2_pgrp,SIGTERM);
+  if (r) warninge("(stage) killpg failed");
 }
 
-static void shbang_opts(const char *const **argv_io,
-			const struct cmdinfo *cmdinfos) {
-  myopt(argv_io, cmdinfos);
+static void alarm_handler(int dummy) {
+  if (out_of_date)
+    /* second timeout */
+    exit(0); /* transfers control to atexit_handler */
 
-  interp = *(*argv_io)++;
-  if (!interp) errx(127,"need interpreter argument");
+  out_of_date = check_garbage_vs(&baseline_time);
+  queue_alarm();
 }
 
-int main(int argc, const char *const *argv) {
-  const char *smashedopt;
-
-  if (argc>=2 &&
-      (smashedopt = argv[1]) &&
-      smashedopt[0]=='-' &&
-      (strchr(smashedopt,' ') || strchr(smashedopt,','))) {
-    /* single argument containg all the options and <interp> */
-    argv += 2; /* eat argv[0] and smashedopt */
-    const char *split_args[MAX_OPTS+1];
-    int split_argc = 0;
-    split_args[split_argc++] = argv[0];
-    for (;;) {
-      if (split_argc >= MAX_OPTS) errx(127,"too many options in combined arg");
-      split_args[split_argc++] = smashedopt;
-      if (smashedopt[0] != '-') /* never true on first iteration */
-	break;
-      char *delim = strchr(smashedopt,' ');
-      if (!delim) delim = strchr(smashedopt,',');
-      if (!delim)
-	errx(127,"combined arg lacks <interpreter>");
-      *delim = 0;
-      smashedopt = delim+1;
+static void child_handler(int dummy) {
+  for (;;) {
+    int status;
+    pid_t got = waitpid(-1, &status, WNOHANG);
+    if (got == (pid_t)-1) diee("(stage2) waitpid");
+    if (got != script_child) {
+      warning("(stage2) waitpid got status %d for unknown child [%lu]",
+	      status, (unsigned long)got);
+      continue;
+    }
+    if (WIFEXITED(status)) {
+      int v = WEXITSTATUS(status);
+      if (v) warning("program failed with error exit status %d", v);
+      exit(status);
+    } else if (WIFSIGNALED(status)) {
+      int s = WTERMSIG(status);
+      warning("program died due to fatal signal %s%s",
+	      strsignal(s), WCOREDUMP(status) ? " (core dumped" : "");
+      assert(status & 0xff);
+      exit(status & 0xff);
+    } else {
+      die("program failed with crazy wait status %#x", status);
     }
-    assert(split_argc <= MAX_OPTS);
-    split_args[split_argc++] = 0;
+  }
+  exit(127);
+}
+
+static void setup_handlers(void) {
+  struct sigaction sa;
+  int r;
+
+  r = atexit(atexit_handler);
+  if (r) diee("(stage2) atexit");
 
-    const char *const *split_argv = split_args;
+  sigemptyset(&sa.sa_mask);
+  sigaddset(&sa.sa_mask, SIGALRM);
+  sigaddset(&sa.sa_mask, SIGCHLD);
+  sa.sa_flags = 0;
 
-    shbang_opts(&split_argv, cmdinfos);
-    /* sets interp */
-    if (!split_argv) errx(127,"combined arg too many non-option arguments");
-  } else {
-    shbang_opts(&argv, cmdinfos);
+  r = sigprocmask(SIG_BLOCK, &sa.sa_mask, 0);
+  if (r) diee("(stage2) sigprocmask(SIG_BLOCK,)");
+
+  sa.sa_handler = alarm_handler;
+  r = sigaction(SIGALRM, &sa, 0);
+  if (r) diee("(stage2) sigaction SIGALRM");
+
+  sa.sa_flags |= SA_NOCLDSTOP;
+  sa.sa_handler = child_handler;
+  r = sigaction(SIGCHLD, &sa, 0);
+  if (r) diee("(stage2) sigaction SIGCHLD");
+}
+
+static void spawn_script(void) {
+  int r;
+  int errpipes[2];
+
+  r = pipe(errpipes);
+  if (r) diee("(stage2) pipe");
+
+  script_child = fork();
+  if (script_child == (pid_t)-1) diee("(stage2) fork");
+  if (!script_child) {
+    r = close(errpipes[0]);
+    if (r) diee("(stage2 child) close errpipes[0]");
+
+    r = dup2(errpipes[1], 2);
+    if (r != 2) diee("(stage2 child) dup2 stderr");
+
+    execlp(interp,
+	   interp, script, (char*)0);
+    diee("(stage2) exec interpreter (`%s', for `%s')\n",interp,script);
   }
 
-  script = *argv++;
-  if (!script) errx(127,"need script argument");
-  if (*argv) errx(127,"too many arguments");
+  r = close(errpipes[1]);
+  if (r) diee("(stage2) close errpipes[1]");
+
+  errpipe = errpipes[0];
+  r = fcntl(errpipe, F_SETFL, O_NONBLOCK);
+  if (r) diee("(stage2) set errpipe nonblocking");
+}
+
+static void queue_alarm(void) {
+  alarm(check_interval);
+}
 
-  find_socket_path();
+static void start_logging(void) {
+  int r;
 
-  check_garbage();
+  openlog(script, LOG_NOWAIT|LOG_PID, LOG_USER);
+  logging = 1;
+  r = dup2(1,2);
+  if (r!=2) diee("dup2 stdout to stderr");
+}
 
-  if (debugmode) {
-    printf("socket: %s\n",socket_path);
-    printf("interp: %s\n",interp);
-    printf("script: %s\n",script);
+static void errpipe_readable(void) {
+  static char buf[1024];
+  static int pending;
+
+  /* %: does not contain newlines
+   * _: empty (garbage)
+   */ 
+
+  /*           %%%%%%%%%%%__________________ */
+  /*                      ^ pending          */
+
+  for (;;) {
+    int avail = sizeof(buf) - pending;
+    ssize_t got = read(errpipe, buf+pending, avail);
+    if (got==-1) {
+      if (errno==EINTR) continue;
+      else if (errno==EWOULDBLOCK || errno==EAGAIN) return;
+      else diee("(stage2) errpipe read");
+      got = 0;
+    } else if (got==0) {
+      warning("program closed its stderr fd");
+      errpipe = -1;
+      return;
+    }
+    int scanned = pending;
+    pending += got;
+    int eaten = 0;
+    for (;;) {
+      const char *newline = memchr(buf+scanned, '\n', pending-scanned);
+      int printupto, eat;
+      if (newline) {
+	printupto = newline-buf;
+	eat = printupto + 1;
+      } else if (!eaten && pending==sizeof(buf)) { /* overflow */
+	printupto = pending;
+	eat = printupto;
+      } else {
+	break;
+      }
+      syslog(LOG_ERR,"stderr: %.*s", printupto-eaten, buf+eaten);
+      eaten += eat;
+      scanned = eaten;
+    }
+    pending -= eaten;
+    memmove(buf, buf+eaten, pending);
   }
+}     
 
-  exit(0);
+static void await_something(void) {
+  int r;
+  sigset_t mask;
+  sigemptyset(&mask);
+
+  for (;;) {
+    fd_set rfds;
+    FD_ZERO(&rfds);
+    if (errpipe >= 0)
+      FD_SET(errpipe, &rfds);
+    r = pselect(errpipe+1, &rfds,0,0, 0, &mask);
+    if (r==-1) {
+      if (errno != EINTR) diee("(stage2) sigsuspend");
+      continue;
+    }
+    assert(r>0);
+    assert(FD_ISSET(errpipe, &rfds));
+    errpipe_readable();
+  }
 }