Add mspawn functions to cspawn.h; move everything to libenvexec

Signed-off-by: Laurent Bercot <ska@appnovation.com>

19 files changed, 688 insertions, 32 deletions

diff --git a/src/libenvexec/child_spawn.c b/src/libenvexec/child_spawn.c
new file mode 100644
index 0000000..164f1b2
--- /dev/null
+++ b/src/libenvexec/child_spawn.c
@@ -0,0 +1,61 @@
+/* ISC license. */
+
+#include <string.h>
+#include <unistd.h>
+
+#include <skalibs/types.h>
+#include <skalibs/djbunix.h>
+#include <skalibs/env.h>
+#include <skalibs/cspawn.h>
+
+pid_t child_spawn (char const *prog, char const *const *argv, char const *const *envp, int *fds, size_t n)
+{
+  pid_t pid ;
+  cspawn_fileaction fa[2] =
+  {
+    [0] = { .type = CSPAWN_FA_MOVE, .x = { .fd2 = { [0] = 1 } } },
+    [1] = { .type = CSPAWN_FA_MOVE, .x = { .fd2 = { [0] = 0 } } }
+  } ;
+  size_t m = sizeof(SKALIBS_CHILD_SPAWN_FDS_ENVVAR) ;
+  size_t envlen = env_len(envp) ;
+  size_t i = 0 ;
+  int p[n ? n : 1][2] ;
+  char const *newenv[envlen + 2] ;
+  char modifs[m + 1 + n * UINT_FMT] ;
+
+  for (; i < n ; i++)
+  {
+    if (pipe(p[i]) == -1) goto errpi ;
+    if ((ndelay_on(p[i][i & 1]) == -1) || (coe(p[i][i & 1]) == -1)) goto errpip ;
+  }
+
+  memcpy(modifs, SKALIBS_CHILD_SPAWN_FDS_ENVVAR "=", sizeof(SKALIBS_CHILD_SPAWN_FDS_ENVVAR)) ;
+  for (i = 2 ; i < n ; i++)
+  {
+    m += uint_fmt(modifs + m, p[i][!(i & 1)]) ;
+    if (i+1 < n) modifs[m++] = ',' ;
+  }
+  modifs[m++] = 0 ;
+  env_mergen(newenv, envlen + 2, envp, envlen, modifs, m, 1) ;
+  if (n) fa[0].x.fd2[1] = p[0][1] ;
+  if (n >= 2) fa[1].x.fd2[1] = p[1][0] ;
+  pid = cspawn(prog, argv, newenv, CSPAWN_FLAGS_SIGBLOCKNONE, fa, n < 2 ? n : 2) ;
+  if (!pid) goto errpi ;
+
+  for (i = 0 ; i < n ; i++)
+  {
+    fd_close(p[i][!(i & 1)]) ;
+    fds[i] = p[i][i & 1] ;
+  }
+  return pid ;
+
+ errpip:
+  i++ ;
+ errpi:
+  while (i--)
+  {
+    fd_close(p[i][1]) ;
+    fd_close(p[i][0]) ;
+  }
+  return 0 ;
+}
diff --git a/src/libenvexec/child_spawn0.c b/src/libenvexec/child_spawn0.c
new file mode 100644
index 0000000..b1353b6
--- /dev/null
+++ b/src/libenvexec/child_spawn0.c
@@ -0,0 +1,8 @@
+/* ISC license. */
+
+#include <skalibs/cspawn.h>
+
+pid_t child_spawn0 (char const *prog, char const *const *argv, char const *const *envp)
+{
+  return cspawn(prog, argv, envp, CSPAWN_FLAGS_SIGBLOCKNONE, 0, 0) ;
+}
diff --git a/src/libenvexec/child_spawn1_internal.c b/src/libenvexec/child_spawn1_internal.c
new file mode 100644
index 0000000..e65b588
--- /dev/null
+++ b/src/libenvexec/child_spawn1_internal.c
@@ -0,0 +1,27 @@
+/* ISC license. */
+
+#include <skalibs/djbunix.h>
+#include <skalibs/cspawn.h>
+#include "cspawn-internal.h"
+
+pid_t child_spawn1_internal (char const *prog, char const *const *argv, char const *const *envp, int *p, int to)
+{
+  pid_t pid ;
+  cspawn_fileaction fa[3] =
+  {
+    [0] = { .type = CSPAWN_FA_CLOSE, .x = { .fd = p[!(to & 1)]} },
+    [1] = { .type = CSPAWN_FA_MOVE, .x = { .fd2 = { [0] = to & 1, [1] = p[to & 1] } } },
+    [2] = { .type = CSPAWN_FA_COPY, .x = { .fd2 = { [0] = !(to & 1), [1] = to & 1 } } }
+  } ;
+
+  pid = cspawn(prog, argv, envp, CSPAWN_FLAGS_SIGBLOCKNONE, fa, 2 + !!(to & 2)) ;
+  if (!pid) goto err ;
+
+  fd_close(p[to & 1]) ;
+  return pid ;
+
+ err:
+  fd_close(p[1]) ;
+  fd_close(p[0]) ;
+  return 0 ;
+}
diff --git a/src/libenvexec/child_spawn1_pipe.c b/src/libenvexec/child_spawn1_pipe.c
new file mode 100644
index 0000000..a31e091
--- /dev/null
+++ b/src/libenvexec/child_spawn1_pipe.c
@@ -0,0 +1,17 @@
+/* ISC license. */
+
+#include <unistd.h>
+
+#include <skalibs/cspawn.h>
+#include "cspawn-internal.h"
+
+pid_t child_spawn1_pipe (char const *prog, char const *const *argv, char const *const *envp, int *fd, int to)
+{
+  pid_t pid ;
+  int p[2] ;
+  if (pipe(p) < 0) return 0 ;
+  pid = child_spawn1_internal(prog, argv, envp, p, !!to) ;
+  if (!pid) return 0 ;
+  *fd = p[!to] ;
+  return pid ;
+}
diff --git a/src/libenvexec/child_spawn1_socket.c b/src/libenvexec/child_spawn1_socket.c
new file mode 100644
index 0000000..684842e
--- /dev/null
+++ b/src/libenvexec/child_spawn1_socket.c
@@ -0,0 +1,16 @@
+/* ISC license. */
+
+#include <skalibs/socket.h>
+#include <skalibs/cspawn.h>
+#include "cspawn-internal.h"
+
+pid_t child_spawn1_socket (char const *prog, char const *const *argv, char const *const *envp, int *fd)
+{
+  pid_t pid ;
+  int p[2] ;
+  if (ipc_pair_b(p) < 0) return 0 ;
+  pid = child_spawn1_internal(prog, argv, envp, p, 3) ;
+  if (!pid) return 0 ;
+  *fd = p[0] ;
+  return pid ;
+}
diff --git a/src/libenvexec/child_spawn2.c b/src/libenvexec/child_spawn2.c
new file mode 100644
index 0000000..f287c0b
--- /dev/null
+++ b/src/libenvexec/child_spawn2.c
@@ -0,0 +1,39 @@
+/* ISC license. */
+
+#include <unistd.h>
+
+#include <skalibs/djbunix.h>
+#include <skalibs/cspawn.h>
+
+pid_t child_spawn2 (char const *prog, char const *const *argv, char const *const *envp, int *fds)
+{
+  pid_t pid ;
+  int p[2][2] ;
+  if (pipe(p[0]) == -1) return 0 ;
+  if (ndelay_on(p[0][0]) == -1 || coe(p[0][0]) == -1 || pipe(p[1]) == -1) goto errp ;
+  if (ndelay_on(p[1][1]) == -1 || coe(p[1][1]) == -1) goto err ;
+
+  {
+    cspawn_fileaction fa[2] =
+    {
+      [0] = { .type = CSPAWN_FA_MOVE, .x = { .fd2 = { [0] = fds[0], [1] = p[1][0] } } },
+      [1] = { .type = CSPAWN_FA_MOVE, .x = { .fd2 = { [0] = fds[1], [1] = p[0][1] } } }
+    } ;
+    pid = cspawn(prog, argv, envp, CSPAWN_FLAGS_SIGBLOCKNONE, fa, 2) ;
+    if (!pid) goto err ;
+  }
+
+  fd_close(p[0][1]) ;
+  fd_close(p[1][0]) ;
+  fds[0] = p[0][0] ;
+  fds[1] = p[1][1] ;
+  return pid ;
+
+ err:
+  fd_close(p[1][1]) ;
+  fd_close(p[1][0]) ;
+ errp:
+  fd_close(p[0][1]) ;
+  fd_close(p[0][0]) ;
+  return 0 ;
+}
diff --git a/src/libenvexec/child_spawn3.c b/src/libenvexec/child_spawn3.c
new file mode 100644
index 0000000..75551d2
--- /dev/null
+++ b/src/libenvexec/child_spawn3.c
@@ -0,0 +1,55 @@
+/* ISC license. */
+
+#include <unistd.h>
+
+#include <skalibs/types.h>
+#include <skalibs/env.h>
+#include <skalibs/djbunix.h>
+#include <skalibs/cspawn.h>
+
+pid_t child_spawn3 (char const *prog, char const *const *argv, char const *const *envp, int *fds)
+{
+  pid_t pid ;
+  int p[3][2] ;
+
+  if (pipe(p[0]) == -1) return 0 ;
+  if (ndelay_on(p[0][0]) == -1 || coe(p[0][0]) == -1 || pipe(p[1]) == -1) goto errp0 ;
+  if (ndelay_on(p[1][1]) == -1 || coe(p[1][1]) == -1 || pipe(p[2]) == -1) goto errp1 ;
+  if (ndelay_on(p[2][0]) == -1 || coe(p[2][0]) == -1) goto err ;
+
+  {
+    cspawn_fileaction fa[2] =
+    {
+      [0] = { .type = CSPAWN_FA_MOVE, .x = { .fd2 = { [0] = fds[0], [1] = p[1][0] } } },
+      [1] = { .type = CSPAWN_FA_MOVE, .x = { .fd2 = { [0] = fds[1], [1] = p[0][1] } } }
+    } ;
+    size_t envlen = env_len(envp) ;
+    size_t m = sizeof(SKALIBS_CHILD_SPAWN_FDS_ENVVAR) ;
+    char modifs[sizeof(SKALIBS_CHILD_SPAWN_FDS_ENVVAR) + UINT_FMT] = SKALIBS_CHILD_SPAWN_FDS_ENVVAR "=" ;
+    char const *newenv[envlen + 2] ;
+    m += uint_fmt(modifs + sizeof(SKALIBS_CHILD_SPAWN_FDS_ENVVAR), p[2][1]) ;
+    modifs[m++] = 0 ;
+    env_mergen(newenv, envlen + 2, envp, envlen, modifs, m, 1) ;
+    pid = cspawn(prog, argv, newenv, CSPAWN_FLAGS_SIGBLOCKNONE, fa, 2) ;
+    if (!pid) goto err ;
+  }
+
+  fd_close(p[2][1]) ;
+  fd_close(p[1][0]) ;
+  fd_close(p[0][1]) ;
+  fds[0] = p[0][0] ;
+  fds[1] = p[1][1] ;
+  fds[2] = p[2][0] ;
+  return pid ;
+
+ err:
+  fd_close(p[2][1]) ;
+  fd_close(p[2][0]) ;
+ errp1:
+  fd_close(p[1][1]) ;
+  fd_close(p[1][0]) ;
+ errp0:
+  fd_close(p[0][1]) ;
+  fd_close(p[0][0]) ;
+  return 0 ;
+}
diff --git a/src/libenvexec/cspawn-internal.h b/src/libenvexec/cspawn-internal.h
new file mode 100644
index 0000000..0e5efc7
--- /dev/null
+++ b/src/libenvexec/cspawn-internal.h
@@ -0,0 +1,10 @@
+/* ISC license. */
+
+#ifndef CSPAWN_INTERNAL_H
+#define CSPAWN_INTERNAL_H
+
+#include <sys/types.h>
+
+extern pid_t child_spawn1_internal (char const *, char const *const *, char const *const *, int *, int) ;
+
+#endif
diff --git a/src/libenvexec/cspawn.c b/src/libenvexec/cspawn.c
new file mode 100644
index 0000000..683a0a3
--- /dev/null
+++ b/src/libenvexec/cspawn.c
@@ -0,0 +1,297 @@
+/* ISC license. */
+
+#include <skalibs/sysdeps.h>
+
+#ifdef SKALIBS_HASPOSIXSPAWN
+#include <skalibs/nonposix.h>
+#endif
+
+#include <errno.h>
+#include <unistd.h>
+
+#include <skalibs/allreadwrite.h>
+#include <skalibs/sig.h>
+#include <skalibs/djbunix.h>
+#include <skalibs/selfpipe.h>
+#include <skalibs/exec.h>
+#include <skalibs/cspawn.h>
+
+static inline void cspawn_child_exec (char const *prog, char const *const *argv, char const *const *envp, uint16_t flags, cspawn_fileaction const *fa, size_t n)
+{
+  for (size_t i = 0 ; i < n ; i++)
+  {
+    switch (fa[i].type)
+    {
+      case CSPAWN_FA_CLOSE : fd_close(fa[i].x.fd) ; break ;
+      case CSPAWN_FA_COPY :
+        if (fd_copy(fa[i].x.fd2[0], fa[i].x.fd2[1]) == -1) return ;
+        break ;
+      case CSPAWN_FA_MOVE :
+        if (fd_move(fa[i].x.fd2[0], fa[i].x.fd2[1]) == -1) return ;
+        if (fa[i].x.fd2[0] == fa[i].x.fd2[1] && uncoe(fa[i].x.fd2[0]) == -1) return ;
+        break ;
+      case CSPAWN_FA_OPEN :
+      {
+        int fd = open3(fa[i].x.openinfo.file, fa[i].x.openinfo.oflag, fa[i].x.openinfo.mode) ;
+        if (fd == -1) return ;
+        if (fd_move(fa[i].x.openinfo.fd, fd) == -1) return ;
+        break ;
+      }
+      case CSPAWN_FA_CHDIR :
+        if (chdir(fa[i].x.path) == -1) return ;
+        break ;
+      case CSPAWN_FA_FCHDIR :
+        if (fchdir(fa[i].x.fd) == -1) return ;
+        break ;
+      default :
+        errno = EINVAL ; return ;
+    }
+  }
+
+  if (flags & CSPAWN_FLAGS_SELFPIPE_FINISH) selfpipe_finish() ;
+  if (flags & CSPAWN_FLAGS_SIGBLOCKNONE) sig_blocknone() ;
+  if (flags & CSPAWN_FLAGS_SETSID) setsid() ;
+
+  exec_ae(prog, argv, envp) ;
+}
+
+static inline pid_t cspawn_fork (char const *prog, char const *const *argv, char const *const *envp, uint16_t flags, cspawn_fileaction const *fa, size_t n)
+{
+  pid_t pid ;
+  int p[2] ;
+  char c ;
+
+  if (pipecoe(p) == -1) return 0 ;
+  pid = fork() ;
+  if (pid == -1)
+  {
+    fd_close(p[1]) ;
+    fd_close(p[0]) ;
+    return 0 ;
+  }
+  if (!pid)
+  {
+    cspawn_child_exec(prog, argv, envp, flags, fa, n) ;
+    c = errno ;
+    fd_write(p[1], &c, 1) ;
+    _exit(127) ;
+  }
+
+  fd_close(p[1]) ;
+  p[1] = fd_read(p[0], &c, 1) ;
+  if (p[1] < 0)
+  {
+    fd_close(p[0]) ;
+    return 0 ;
+  }
+  fd_close(p[0]) ;
+  if (p[1])
+  {
+    wait_pid(pid, &p[0]) ;
+    errno = (unsigned char)c ;
+    return 0 ;
+  }
+  return pid ;
+}
+
+ /*
+    guess who has a buggy posix_spawn() *and* doesn't have waitid() to work around it?
+    if you guessed OpenBSD, you're right!
+ */
+
+#if defined(SKALIBS_HASPOSIXSPAWN) && (!defined(SKALIBS_HASPOSIXSPAWNEARLYRETURN) || defined(SKALIBS_HASWAITID))
+
+#include <signal.h>
+#include <stdlib.h>
+#include <spawn.h>
+
+#include <skalibs/config.h>
+#include <skalibs/djbunix.h>
+
+#ifdef SKALIBS_HASPOSIXSPAWNEARLYRETURN
+
+#include <sys/wait.h>
+
+static inline pid_t cspawn_workaround (pid_t pid, int const *p)
+{
+  siginfo_t si ;
+  int e ;
+  ssize_t r ;
+  char c ;
+
+  fd_close(p[1]) ;
+  r = fd_read(p[0], &c, 1) ;
+  fd_close(p[0]) ;
+  if (r == -1) return 0 ;
+  if (r) return (errno = EILSEQ, 0) ;  /* child wrote, wtf */
+
+  do e = waitid(P_PID, pid, &si, WEXITED | WNOHANG | WNOWAIT) ;
+  while (e == -1 && errno == EINTR) ;
+  if (e == -1) return pid ;  /* we're in trouble, but don't leak a child */
+  if (!si.si_pid) return pid ;  /* child is running */
+  if (si.si_code != CLD_EXITED || si.si_status != 127) return pid ; /* child died after execve(), let caller handle it */
+  /*
+    child exited 127, so either execve() failed, which is what we want to catch,
+    or it raced like a mofo, execve()d and then exited 127 on its own, in which
+    case, tough luck, it never existed.
+  */
+  wait_pid(pid, 0) ;
+  return (errno = 0, 0) ;
+}
+
+#endif
+
+static inline pid_t cspawn_pspawn (char const *prog, char const *const *argv, char const *const *envp, uint16_t flags, cspawn_fileaction const *fa, size_t n)
+{
+  pid_t pid ;
+  posix_spawnattr_t attr ;
+  posix_spawn_file_actions_t actions ;
+  int e ;
+  int nopath = !getenv("PATH") ;
+#ifdef SKALIBS_HASPOSIXSPAWNEARLYRETURN
+  int p[2] ;
+  if (pipecoe(p) == -1) return 0 ;
+#endif
+
+  if (flags)
+  {
+    short pfff = 0 ;
+    e = posix_spawnattr_init(&attr) ;
+    if (e) goto err ;
+    if (flags & (CSPAWN_FLAGS_SIGBLOCKNONE | CSPAWN_FLAGS_SELFPIPE_FINISH))
+    {
+      sigset_t set ;
+      sigemptyset(&set) ;
+      e = posix_spawnattr_setsigmask(&attr, &set) ;
+      if (e) goto errattr ;
+      pfff |= POSIX_SPAWN_SETSIGMASK ;
+    }
+#ifdef SKALIBS_HASPOSIXSPAWNSETSID
+    if (flags & CSPAWN_FLAGS_SETSID) pfff |= POSIX_SPAWN_SETSID ;
+#else
+#ifdef SKALIBS_HASPOSIXSPAWNSETSIDNP
+    if (flags & CSPAWN_FLAGS_SETSID) pfff |= POSIX_SPAWN_SETSID_NP ;
+#endif
+#endif
+    e = posix_spawnattr_setflags(&attr, pfff) ;
+    if (e) goto errattr ;
+  }
+
+  if (n)
+  {
+    e = posix_spawn_file_actions_init(&actions) ;
+    if (e) goto errattr ;
+    for (size_t i = 0 ; i < n ; i++)
+    {
+      switch (fa[i].type)
+      {
+        case CSPAWN_FA_CLOSE :
+          e = posix_spawn_file_actions_addclose(&actions, fa[i].x.fd) ;
+          if (e) goto erractions ;
+          break ;
+        case CSPAWN_FA_COPY :
+          e = posix_spawn_file_actions_adddup2(&actions, fa[i].x.fd2[1], fa[i].x.fd2[0]) ;
+          if (e) goto erractions ;
+          break ;
+        case CSPAWN_FA_MOVE :
+          e = posix_spawn_file_actions_adddup2(&actions, fa[i].x.fd2[1], fa[i].x.fd2[0]) ;
+          if (e) goto erractions ;
+          if (fa[i].x.fd2[0] != fa[i].x.fd2[1])
+          {
+            e = posix_spawn_file_actions_addclose(&actions, fa[i].x.fd2[1]) ;
+            if (e) goto erractions ;
+          }
+          break ;
+        case CSPAWN_FA_OPEN :
+          e = posix_spawn_file_actions_addopen(&actions, fa[i].x.openinfo.fd, fa[i].x.openinfo.file, fa[i].x.openinfo.oflag, fa[i].x.openinfo.mode) ;
+          if (e) goto erractions ;
+          break ;
+#ifdef SKALIBS_HASPOSIXSPAWNCHDIR
+        case CSPAWN_FA_CHDIR :
+          e = posix_spawn_file_actions_addchdir(&actions, fa[i].x.path) ;
+          if (e) goto erractions ;
+          break ;
+        case CSPAWN_FA_FCHDIR :
+          e = posix_spawn_file_actions_addfchdir(&actions, fa[i].x.fd) ;
+          if (e) goto erractions ;
+          break ;
+#else
+#ifdef SKALIBS_HASPOSIXSPAWNCHDIRNP
+        case CSPAWN_FA_CHDIR :
+          e = posix_spawn_file_actions_addchdir_np(&actions, fa[i].x.path) ;
+          if (e) goto erractions ;
+          break ;
+        case CSPAWN_FA_FCHDIR :
+          e = posix_spawn_file_actions_addfchdir_np(&actions, fa[i].x.fd) ;
+          if (e) goto erractions ;
+          break ;
+#endif
+#endif
+        default :
+          e = EINVAL ;
+          goto erractions ;
+      }
+    }
+  }
+
+  if (nopath && (setenv("PATH", SKALIBS_DEFAULTPATH, 0) == -1)) { e = errno ; goto erractions ; }
+  e = posix_spawnp(&pid, prog, n ? &actions : 0, flags ? &attr : 0, (char *const *)argv, (char *const *)envp) ;
+  if (nopath) unsetenv("PATH") ;
+  if (e) goto erractions ;
+
+  if (n) posix_spawn_file_actions_destroy(&actions) ;
+  if (flags) posix_spawnattr_destroy(&attr) ;
+#ifdef SKALIBS_HASPOSIXSPAWNEARLYRETURN
+  return cspawn_workaround(pid, p) ;
+#else
+  return pid ;
+#endif
+
+ erractions:
+  if (n) posix_spawn_file_actions_destroy(&actions) ;
+ errattr:
+  if (flags) posix_spawnattr_destroy(&attr) ;
+ err:
+#ifdef SKALIBS_HASPOSIXSPAWNEARLYRETURN
+  fd_close(p[1]) ;
+  fd_close(p[0]) ;
+#endif
+  errno = e ;
+  return 0 ;
+}
+
+#if (defined(SKALIBS_HASPOSIXSPAWNSETSID) || defined(SKALIBS_HASPOSIXSPAWNSETSIDNP)) && (defined(SKALIBS_HASPOSIXSPAWNCHDIR) || defined(SKALIBS_HASPOSIXSPAWNCHDIRNP))
+
+pid_t cspawn (char const *prog, char const *const *argv, char const *const *envp, uint16_t flags, cspawn_fileaction const *fa, size_t n)
+{
+  return cspawn_pspawn(prog, argv, envp, flags, fa, n) ;
+}
+
+#else
+
+pid_t cspawn (char const *prog, char const *const *argv, char const *const *envp, uint16_t flags, cspawn_fileaction const *fa, size_t n)
+{
+#if !defined(SKALIBS_HASPOSIXSPAWNSETSID) && !defined(SKALIBS_HASPOSIXSPAWNSETSIDNP)
+  if (flags & CSPAWN_FLAGS_SETSID) goto dofork ;
+#endif
+#if !defined(SKALIBS_HASPOSIXSPAWNCHDIR) && !defined(SKALIBS_HASPOSIXSPAWNCHDIRNP)
+  for (size_t i = 0 ; i < n ; i++)
+    if (fa[i].type == CSPAWN_FA_CHDIR || fa[i].type == CSPAWN_FA_FCHDIR)
+      goto dofork ;
+#endif
+  return cspawn_pspawn(prog, argv, envp, flags, fa, n) ;
+
+ dofork:
+  return cspawn_fork(prog, argv, envp, flags, fa, n) ;
+}
+
+#endif
+
+#else
+
+pid_t cspawn (char const *prog, char const *const *argv, char const *const *envp, uint16_t flags, cspawn_fileaction const *fa, size_t n)
+{
+  return cspawn_fork(prog, argv, envp, flags, fa, n) ;
+}
+
+#endif
diff --git a/src/libenvexec/env_merge.c b/src/libenvexec/env_merge.c
index ac3e17c..b6281ee 100644
--- a/src/libenvexec/env_merge.c
+++ b/src/libenvexec/env_merge.c
@@ -1,9 +1,31 @@
 /* ISC license. */
 
+#include <string.h>
+#include <errno.h>
+
 #include <skalibs/bytestr.h>
 #include <skalibs/env.h>
 
 size_t env_merge (char const **v, size_t vmax, char const *const *envp, size_t envlen, char const *modifs, size_t modiflen)
 {
-  return env_mergen(v, vmax, envp, envlen, modifs, modiflen, byte_count(modifs, modiflen, '\0')) ;
+  size_t vlen = envlen ;
+  size_t i = 0 ;
+  if (envlen >= vmax) return 0 ;
+  for (; i < envlen ; i++) v[i] = envp[i] ;
+  for (i = 0 ; i < modiflen ; i += strlen(modifs + i) + 1)
+  {
+    size_t split = str_chr(modifs + i, '=') ;
+    size_t j = 0 ;
+    for (; j < vlen ; j++)
+      if (!strncmp(modifs + i, v[j], split) && (v[j][split] == '=')) break ;
+    if (j < vlen) v[j] = v[--vlen] ;
+    if (modifs[i + split])
+    {
+      if (vlen >= vmax) return 0 ;
+      v[vlen++] = modifs + i ;
+    }
+  }
+  if (vlen >= vmax) return 0 ;
+  v[vlen++] = 0 ;
+  return vlen ;
 }
diff --git a/src/libenvexec/env_mergen.c b/src/libenvexec/env_mergen.c
deleted file mode 100644
index 64a77cb..0000000
--- a/src/libenvexec/env_mergen.c
+++ /dev/null
@@ -1,31 +0,0 @@
-/* ISC license. */
-
-#include <string.h>
-#include <errno.h>
-
-#include <skalibs/bytestr.h>
-#include <skalibs/env.h>
-
-size_t env_mergen (char const **v, size_t vmax, char const *const *envp, size_t envlen, char const *modifs, size_t modiflen, size_t n)
-{
-  size_t vlen = envlen ;
-  size_t i = 0 ;
-  if (envlen >= vmax) return 0 ;
-  for (; i < envlen ; i++) v[i] = envp[i] ;
-  for (i = 0 ; i < modiflen ; i += strlen(modifs + i) + 1)
-  {
-    size_t split = str_chr(modifs + i, '=') ;
-    size_t j = 0 ;
-    for (; j < vlen ; j++)
-      if (!strncmp(modifs + i, v[j], split) && (v[j][split] == '=')) break ;
-    if (j < vlen) v[j] = v[--vlen] ;
-    if (modifs[i + split])
-    {
-      if (vlen >= vmax) return 0 ;
-      v[vlen++] = modifs + i ;
-    }
-  }
-  if (vlen >= vmax) return 0 ;
-  v[vlen++] = 0 ;
-  return vlen ;
-}
diff --git a/src/libenvexec/gcspawn.c b/src/libenvexec/gcspawn.c
new file mode 100644
index 0000000..7e9e602
--- /dev/null
+++ b/src/libenvexec/gcspawn.c
@@ -0,0 +1,48 @@
+/* ISC license. */
+
+#include <sys/wait.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include <skalibs/types.h>
+#include <skalibs/allreadwrite.h>
+#include <skalibs/djbunix.h>
+#include <skalibs/cspawn.h>
+
+pid_t gcspawn (char const *prog, char const *const *argv, char const *const *envp, uint16_t flags, cspawn_fileaction const *fa, size_t n)
+{
+  pid_t pid = 0 ;
+  int wstat ;
+  int p[2] ;
+  char pack[PID_PACK] ;
+  if (pipecoe(p) == -1) return 0 ;
+  pid = fork() ;
+  switch (pid)
+  {
+    case -1:
+    {
+      fd_close(p[1]) ;
+      fd_close(p[0]) ;
+      return 0 ;
+    }
+    case 0:
+    {
+      fd_close(p[0]) ;
+      pid = cspawn(prog, argv, envp, flags, fa, n) ;
+      if (!pid) _exit(errno) ;
+      pid_pack_big(pack, pid) ;
+      _exit(fd_write(p[1], pack, PID_PACK) < PID_PACK ? errno : 0) ;
+    }
+  }
+  fd_close(p[1]) ;
+  if (fd_read(p[0], pack, PID_PACK) < PID_PACK) goto err ;
+  fd_close(p[0]) ;
+  wait_pid(pid, &wstat) ;
+  pid_unpack_big(pack, &pid) ;
+  return pid ;
+
+ err:
+  fd_close(p[0]) ;
+  wait_pid(pid, &wstat) ;
+  return (errno = WIFSIGNALED(wstat) ? EINTR : WEXITSTATUS(wstat), 0) ;
+}
diff --git a/src/libenvexec/gmspawn_afn.c b/src/libenvexec/gmspawn_afn.c
new file mode 100644
index 0000000..dc49017
--- /dev/null
+++ b/src/libenvexec/gmspawn_afn.c
@@ -0,0 +1,11 @@
+/* ISC license. */
+
+#include <skalibs/env.h>
+#include <skalibs/cspawn.h>
+
+pid_t gmspawn_afn (char const *file, char const *const *argv, char const *const *envp, size_t envlen, char const *modif, size_t modiflen, size_t modifn, uint16_t flags, cspawn_fileaction const *fa, size_t n)
+{
+  char const *newenvp[envlen + modifn + 1] ;
+  env_merge(newenvp, envlen + modifn + 1, envp, envlen, modif, modiflen) ;
+  return gcspawn(file, argv, newenvp, flags, fa, n) ;
+}
diff --git a/src/libenvexec/mspawn_af.c b/src/libenvexec/mspawn_af.c
new file mode 100644
index 0000000..97dc877
--- /dev/null
+++ b/src/libenvexec/mspawn_af.c
@@ -0,0 +1,17 @@
+/* ISC license. */
+
+#include <skalibs/stralloc.h>
+#include <skalibs/env.h>
+#include <skalibs/cspawn.h>
+
+static stralloc modifsa = STRALLOC_ZERO ;
+
+int env_mspawn (char const *key, char const *value)
+{
+  return env_addmodif(&modifsa, key, value) ;
+}
+
+pid_t mspawn_af (char const *file, char const *const *argv, char const *const *envp, size_t envlen, uint16_t flags, cspawn_fileaction const *fa, size_t n)
+{
+  return mspawn_afm(file, argv, envp, envlen, modifsa.s, modifsa.len, flags, fa, n) ;
+}
diff --git a/src/libenvexec/mspawn_afm.c b/src/libenvexec/mspawn_afm.c
new file mode 100644
index 0000000..4b3711e
--- /dev/null
+++ b/src/libenvexec/mspawn_afm.c
@@ -0,0 +1,9 @@
+/* ISC license. */
+
+#include <skalibs/bytestr.h>
+#include <skalibs/cspawn.h>
+
+pid_t mspawn_afm (char const *file, char const *const *argv, char const *const *envp, size_t envlen, char const *modif, size_t modiflen, uint16_t flags, cspawn_fileaction const *fa, size_t n)
+{
+  return mspawn_afn(file, argv, envp, envlen, modif, modiflen, byte_count(modif, modiflen, '\0'), flags, fa, n) ;
+}
diff --git a/src/libenvexec/mspawn_afn.c b/src/libenvexec/mspawn_afn.c
new file mode 100644
index 0000000..fe36fca
--- /dev/null
+++ b/src/libenvexec/mspawn_afn.c
@@ -0,0 +1,11 @@
+/* ISC license. */
+
+#include <skalibs/env.h>
+#include <skalibs/cspawn.h>
+
+pid_t mspawn_afn (char const *file, char const *const *argv, char const *const *envp, size_t envlen, char const *modif, size_t modiflen, size_t modifn, uint16_t flags, cspawn_fileaction const *fa, size_t n)
+{
+  char const *newenvp[envlen + modifn + 1] ;
+  env_merge(newenvp, envlen + modifn + 1, envp, envlen, modif, modiflen) ;
+  return cspawn(file, argv, newenvp, flags, fa, n) ;
+}
diff --git a/src/libenvexec/xmspawn_af.c b/src/libenvexec/xmspawn_af.c
new file mode 100644
index 0000000..3e79114
--- /dev/null
+++ b/src/libenvexec/xmspawn_af.c
@@ -0,0 +1,13 @@
+/* ISC license. */
+
+#include <errno.h>
+
+#include <skalibs/strerr.h>
+#include <skalibs/cspawn.h>
+
+pid_t xmspawn_af (char const *file, char const *const *argv, char const *const *envp, size_t envlen, uint16_t flags, cspawn_fileaction const *fa, size_t n)
+{
+  pid_t pid = mspawn_af(file, argv, envp, envlen, flags, fa, n) ;
+  if (!pid) strerr_diefu2sys(errno == ENOENT ? 127 : 126, "spawn ", file) ;
+  return pid ;
+}
diff --git a/src/libenvexec/xmspawn_afm.c b/src/libenvexec/xmspawn_afm.c
new file mode 100644
index 0000000..5335fb1
--- /dev/null
+++ b/src/libenvexec/xmspawn_afm.c
@@ -0,0 +1,13 @@
+/* ISC license. */
+
+#include <errno.h>
+
+#include <skalibs/strerr.h>
+#include <skalibs/cspawn.h>
+
+pid_t xmspawn_afm (char const *file, char const *const *argv, char const *const *envp, size_t envlen, char const *modif, size_t modiflen, uint16_t flags, cspawn_fileaction const *fa, size_t n)
+{
+  pid_t pid = mspawn_afm(file, argv, envp, envlen, modif, modiflen, flags, fa, n) ;
+  if (!pid) strerr_diefu2sys(errno == ENOENT ? 127 : 126, "spawn ", file) ;
+  return pid ;
+}
diff --git a/src/libenvexec/xmspawn_afn.c b/src/libenvexec/xmspawn_afn.c
new file mode 100644
index 0000000..5af7c2e
--- /dev/null
+++ b/src/libenvexec/xmspawn_afn.c
@@ -0,0 +1,13 @@
+/* ISC license. */
+
+#include <errno.h>
+
+#include <skalibs/strerr.h>
+#include <skalibs/cspawn.h>
+
+pid_t xmspawn_afn (char const *file, char const *const *argv, char const *const *envp, size_t envlen, char const *modif, size_t modiflen, size_t modifn, uint16_t flags, cspawn_fileaction const *fa, size_t n)
+{
+  pid_t pid = mspawn_afn(file, argv, envp, envlen, modif, modiflen, modifn, flags, fa, n) ;
+  if (!pid) strerr_diefu2sys(errno == ENOENT ? 127 : 126, "spawn ", file) ;
+  return pid ;
+}