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=96037a32c94daf740ce87cff7cb9178cb2358b3f;hpb=7ac3f0443c9739088fdb316788cf2cc98559f5db;p=chiark-utils.git

diff --git a/cprogs/cgi-fcgi-interp.c b/cprogs/cgi-fcgi-interp.c
index 96037a3..6ea886e 100644
--- a/cprogs/cgi-fcgi-interp.c
+++ b/cprogs/cgi-fcgi-interp.c
@@ -1,10 +1,14 @@
 /*
  * "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
@@ -37,6 +41,16 @@
  *          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(<interp>\0<script>\0))
  *          as the basename of the leafname of the fcgi rendezvous
@@ -113,237 +127,48 @@
  *      kill process group (at second iteration)
  */
 
-#include "common.h"
-
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <errno.h>
-#include <stdbool.h>
-#include <assert.h>
-#include <limits.h>
-
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <sys/utsname.h>
-#include <sys/socket.h>
-#include <sys/un.h>
-#include <sys/file.h>
-#include <unistd.h>
-#include <fcntl.h>
-#include <pwd.h>
-#include <err.h>
-#include <time.h>
-#include <signal.h>
-#include <sys/wait.h>
-	
-#include <nettle/sha.h>
-
-#include "myopt.h"
-
-#define die  common_die
-#define diee common_diee
-
-#define MINHEXHASH 33
+#include "prefork.h"
+#include "timespeccmp.h"
+
 #define STAGE2_VAR "CHIARKUTILS_CGIFCGIINTERP_STAGE2"
 
-static const char *interp, *ident;
+static const char *stage2;
+
+const char our_name[] = "cgi-fcgi-interp";
+
 static int numservers=4, debugmode;
 static int check_interval=300;
 
-const char *stage2;
-
-void diee(const char *m) {
-  err(127, "error: %s failed", m);
-}
+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 }
+};
 
-static void fusagemessage(FILE *f) {
+void fusagemessage(FILE *f) {
   fprintf(f, "usage: #!/usr/bin/cgi-fcgi-interp [<options>]\n");
 }
 
-void usagemessage(void) { fusagemessage(stderr); }
-
-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 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;
+void ident_addinit(void) {
 }
 
-#define MAX_OPTS 5
-
-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, 'c',   1, .call=of_iassign, .iassignto= &check_interval  },
-  { 0 }
-};
-
-static uid_t us;
-static const char *run_base, *script, *socket_path;
-static const char *run_base_mkdir_p;
 static int stderr_copy;
 
-static bool find_run_base_var_run(void) {
-  struct stat stab;
-  char *try;
-  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;
-  }
-  if (stab.st_mode & 0077) {
-    warnx("%s writeable by group or other, falling back to ~\n", try);
-    return 0;
-  }
-  run_base = m_asprintf("%s/%s", try, "cgi-fcgi-interp");
-  return 1;
+static void make_stderr_copy(void) {
+  stderr_copy = dup(2);
+  if (stderr_copy < 0) diee("dup stderr (for copy for stage2)");
 }
 
-static bool find_run_base_home(void) {
-  struct passwd *pw;
-  struct utsname ut;
-  char *dot, *try;
+static void prep_stage2(void) {
   int r;
-
-  pw = getpwuid(us);  if (!pw) diee("getpwent(uid)");
-
-  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;
-
-  run_base_mkdir_p = m_asprintf("%s/%s", pw->pw_dir, ".cgi-fcgi-interp");
-  try = m_asprintf("%/%s", run_base_mkdir_p, ut.nodename);
-  run_base = try;
-  return 1;
+  
+  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);
 }
 
-static void find_socket_path(void) {
-  struct sockaddr_un sun;
-  int r;
-
-  us = getuid();  if (us==(uid_t)-1) diee("getuid");
-
-  find_run_base_var_run() ||
-    find_run_base_home() ||
-    (abort(),0);
-
-  int maxidentlen = sizeof(sun.sun_path) - strlen(run_base) - 10 - 2;
-
-  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);
-
-    int identlen = maxidentlen > 64 ? 64 : maxidentlen;
-    char *hexident = xmalloc(identlen + 2);
-    struct sha256_ctx sc;
-    unsigned char bbuf[32];
-    int i;
-
-    sha256_init(&sc);
-    sha256_update(&sc,strlen(interp)+1,interp);
-    sha256_update(&sc,strlen(script)+1,script);
-    sha256_digest(&sc,sizeof(bbuf),bbuf);
-
-    for (i=0; i<identlen; i += 2)
-      sprintf(hexident+i, "%02x", bbuf[i/2]);
-
-    hexident[identlen] = 0;
-    ident = hexident;
-  }
-
-  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);
-
-  r = mkdir(run_base, 0700);
-  if (r && errno==ENOENT && run_base_mkdir_p) {
-    r = mkdir(run_base_mkdir_p, 0700);
-    if (r) err(127,"mkdir %s (since %s was ENOENT)",run_base_mkdir_p,run_base);
-    r = mkdir(run_base, 0700);
-  }
-  if (r) {
-    if (!(errno == EEXIST))
-      err(127,"mkdir %s",run_base);
-  }
-
-  socket_path = m_asprintf("%s/s%s",run_base,ident);
-}  
-
-/*
- * Regarding the macro timespeccmp:
- *
- * Copyright (c) 1982, 1986, 1993
- *      The Regents of the University of California.  All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in the
- *    documentation and/or other materials provided with the distribution.
- * 4. Neither the name of the University nor the names of its contributors
- *    may be used to endorse or promote products derived from this software
- *    without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- *
- *      @(#)time.h      8.5 (Berkeley) 5/4/95
- * $FreeBSD: head/sys/sys/time.h 275985 2014-12-21 05:07:11Z imp $
- */
-#ifndef timespeccmp
-#define timespeccmp(tvp, uvp, cmp)                                      \
-        (((tvp)->tv_sec == (uvp)->tv_sec) ?                             \
-            ((tvp)->tv_nsec cmp (uvp)->tv_nsec) :                       \
-            ((tvp)->tv_sec cmp (uvp)->tv_sec))
-#endif /*timespeccmp*/
-
-
-
 #ifdef st_mtime
 
 static bool stab_isnewer(const struct stat *a, const struct stat *b) {
@@ -358,7 +183,7 @@ static bool stab_isnewer(const struct stat *a, const struct stat *b) {
 
 static void stab_mtimenow(struct stat *out) {
   int r = clock_gettime(CLOCK_REALTIME, &out->st_mtim);
-  if (r) err(127,"(stage2) clock_gettime");
+  if (r) diee("(stage2) clock_gettime");
   if (debugmode)
     fprintf(stderr,"stab_mtimenow mtim %lu.%06lu\n",
 	    (unsigned long)out->st_mtim.tv_sec,
@@ -372,12 +197,12 @@ static bool stab_isnewer(const struct stat *a, const struct stat *b) {
     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;
+  return a->st_mtime > b->st_mtime;
 }
 
 static void stab_mtimenow(struct stat *out) {
   out->st_mtime = time(NULL);
-  if (baseline_time.st_mtime == (time_t)-1) err(127,"(stage2) time()");
+  if (out->st_mtime == (time_t)-1) diee("(stage2) time()");
   if (debugmode)
     fprintf(stderr,"stab_mtimenow mtime %lu\n",
 	    (unsigned long)out->st_mtime);
@@ -390,14 +215,14 @@ static bool check_garbage_vs(const struct stat *started) {
   int r;
 
   r = lstat(script, &script_stab);
-  if (r) err(127,"lstat script (%s)",script);
+  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) err(127,"stat script (%s0",script);
+    if (r) diee("stat script (%s0",script);
 
     if (stab_isnewer(&script_stab, started))
       return 1;
@@ -414,7 +239,7 @@ static bool check_garbage(void) {
   if (r) {
     if ((errno == ENOENT))
       return 0; /* well, no garbage then */
-    err(127,"stat socket (%s)",socket_path);
+    diee("stat socket (%s)",socket_path);
   }
 
   return check_garbage_vs(&sock_stab);
@@ -428,45 +253,18 @@ static void tidy_garbage(void) {
   int lockfd = -1;
   int r;
 
-  const char *lock_path = m_asprintf("%s/l%s",run_base,ident);
-
-  lockfd = open(lock_path, O_CREAT|O_RDWR, 0600);
-  if (lockfd<0) err(127,"create lock (%s)", lock_path);
-
-  r = flock(lockfd, LOCK_EX);
-  if (r) err(127,"lock lock (%s)", lock_path);
+  lockfd = acquire_lock();
 
   if (check_garbage()) {
     r = unlink(socket_path);
     if (r) {
       if (!(errno == ENOENT))
-	err(127,"remove out-of-date socket (%s)", socket_path);
+	diee("remove out-of-date socket (%s)", socket_path);
     }
   }
 
   r = close(lockfd);
-  if (r) errx(127,"close lock (%s)", lock_path);
-}
-
-static void make_stderr_copy(void) {
-  stderr_copy = dup(2);
-  if (stderr_copy < 0) err(127,"dup stderr (for copy for stage2)");
-}
-
-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) err(127,"set %s (to announce to stage2)", STAGE2_VAR);
-}
-
-static void shbang_opts(const char *const **argv_io,
-			const struct cmdinfo *cmdinfos) {
-  myopt(argv_io, cmdinfos);
-
-  interp = *(*argv_io)++;
-  if (!interp) errx(127,"need interpreter argument");
+  if (r) diee("close lock (%s)", lock_path);
 }
 
 /* stage2 predeclarations */
@@ -475,10 +273,10 @@ 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 argc, const char *const *argv) {
-  const char *smashedopt;
+int main(int unused_argc, const char *const *argv) {
   int r;
 
   stage2 = getenv(STAGE2_VAR);
@@ -490,47 +288,16 @@ int main(int argc, const char *const *argv) {
     assert(r==2);
 
     r = open("/dev/null",O_WRONLY);
-    if (r<0) err(127,"open /dev/null as stdout");
+    if (r<0) diee("open /dev/null as stdout");
     if (r>=3) close(r);
-    else if (r!=1) errx(127,"open /dev/null for stdout gave bad fd %d",r);
-  }
+    else if (r!=1) die("open /dev/null for stdout gave bad fd %d",r);
 
-  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;
-    }
-    assert(split_argc <= MAX_OPTS);
-    split_args[split_argc++] = 0;
-
-    const char *const *split_argv = split_args;
-
-    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 = close(stderrfd);
+    if (r) diee("close saved stderr fd");
   }
 
-  script = *argv++;
-  if (!script) errx(127,"need script argument");
-  if (*argv) errx(127,"too many arguments");
+  process_opts(&argv);
+  if (!script) badusage("need script argument");
 
   if (!stage2) {
     
@@ -557,7 +324,7 @@ int main(int argc, const char *const *argv) {
 	   script,
 	   m_asprintf("%d", numservers),
 	   (char*)0);
-    err(127,"exec cgi-fcgi");
+    diee("exec cgi-fcgi");
     
   } else { /*stage2*/
 
@@ -566,6 +333,7 @@ int main(int argc, const char *const *argv) {
     setup_handlers();
     spawn_script();
     queue_alarm();
+    start_logging();
     await_something();
     abort();
 
@@ -582,6 +350,7 @@ int main(int argc, const char *const *argv) {
 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);
@@ -593,17 +362,17 @@ static void become_pgrp(void) {
   stage2_pgrp = getpid();
 
   r = setpgid(0,0);
-  if (r) err(127,"(stage2) setpgid");
+  if (r) diee("(stage2) setpgid");
 }
 
 static void atexit_handler(void) {
   int r;
 
   sighandler_t sigr = signal(SIGTERM,SIG_IGN);
-  if (sigr == SIG_ERR) warn("(stage2) signal(SIGTERM,SIG_IGN)");
+  if (sigr == SIG_ERR) warninge("(stage2) signal(SIGTERM,SIG_IGN)");
 
   r = killpg(stage2_pgrp,SIGTERM);
-  if (r) warn("(stage) killpg failed");
+  if (r) warninge("(stage) killpg failed");
 }
 
 static void alarm_handler(int dummy) {
@@ -619,22 +388,24 @@ static void child_handler(int dummy) {
   for (;;) {
     int status;
     pid_t got = waitpid(-1, &status, WNOHANG);
-    if (got == (pid_t)-1) err(127,"(stage2) waitpid");
+    if (got == (pid_t)-1) diee("(stage2) waitpid");
     if (got != script_child) {
-      warn("(stage2) waitpid got status %d for unknown child [%lu]",
-	   status, (unsigned long)got);
+      warning("(stage2) waitpid got status %d for unknown child [%lu]",
+	      status, (unsigned long)got);
       continue;
     }
     if (WIFEXITED(status)) {
       int v = WEXITSTATUS(status);
-      if (v) warn("program failed with error exit status %d", v);
+      if (v) warning("program failed with error exit status %d", v);
       exit(status);
     } else if (WIFSIGNALED(status)) {
       int s = WTERMSIG(status);
-      err(status & 0xff, "program died due to fatal signal %s%s",
-	  strsignal(s), WCOREDUMP(status) ? " (core dumped" : "");
+      warning("program died due to fatal signal %s%s",
+	      strsignal(s), WCOREDUMP(status) ? " (core dumped" : "");
+      assert(status & 0xff);
+      exit(status & 0xff);
     } else {
-      err(127, "program failed with crazy wait status %#x", status);
+      die("program failed with crazy wait status %#x", status);
     }
   }
   exit(127);
@@ -645,7 +416,7 @@ static void setup_handlers(void) {
   int r;
 
   r = atexit(atexit_handler);
-  if (r) err(127,"(stage2) atexit");
+  if (r) diee("(stage2) atexit");
 
   sigemptyset(&sa.sa_mask);
   sigaddset(&sa.sa_mask, SIGALRM);
@@ -653,40 +424,125 @@ static void setup_handlers(void) {
   sa.sa_flags = 0;
 
   r = sigprocmask(SIG_BLOCK, &sa.sa_mask, 0);
-  if (r) err(127,"(stage2) sigprocmask(SIG_BLOCK,)");
+  if (r) diee("(stage2) sigprocmask(SIG_BLOCK,)");
 
   sa.sa_handler = alarm_handler;
   r = sigaction(SIGALRM, &sa, 0);
-  if (r) err(127,"(stage2) sigaction SIGALRM");
+  if (r) diee("(stage2) sigaction SIGALRM");
 
   sa.sa_flags |= SA_NOCLDSTOP;
   sa.sa_handler = child_handler;
   r = sigaction(SIGCHLD, &sa, 0);
-  if (r) err(127,"(stage2) sigaction SIGCHLD");
+  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) err(127,"(stage2) 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);
-    err(127,"(stage2) exec interpreter (`%s', for `%s')\n",interp,script);
+    diee("(stage2) exec interpreter (`%s', for `%s')\n",interp,script);
   }
+
+  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);
 }
 
+static void start_logging(void) {
+  int r;
+
+  openlog(script, LOG_NOWAIT|LOG_PID, LOG_USER);
+  logging = 1;
+  r = dup2(1,2);
+  if (r!=2) diee("dup2 stdout to stderr");
+}
+
+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);
+  }
+}     
+
 static void await_something(void) {
   int r;
   sigset_t mask;
   sigemptyset(&mask);
 
   for (;;) {
-    r = sigsuspend(&mask);
-    assert(r==-1);
-    if (errno != EINTR) err(127,"(stage2) sigsuspend");
+    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();
   }
 }