[PATCH 2/2] Implement fchdir action for posix_spawn()

[Jonathan Nieder <jrnieder at gmail dot com>]

Even operating systems without COW fork tend to provide a way to set
the working directory for a new process without affecting the current
one.  Provide a convenient interface for semi-portable code to do
that.
---
 NEWS                                               |    4 +++-
 posix/Makefile                                     |    2 +-
 posix/Versions                                     |    3 +++
 posix/spawn.h                                      |    8 ++++++++
 ...faction_addclose.c => spawn_faction_addchdir.c} |   10 +++++-----
 posix/spawn_int.h                                  |    7 ++++++-
 sysdeps/posix/spawni.c                             |    6 ++++++
 7 files changed, 32 insertions(+), 8 deletions(-)
 copy posix/{spawn_faction_addclose.c => spawn_faction_addchdir.c} (86%)

diff --git a/NEWS b/NEWS
index 6c336c2..396c74a 100644
--- a/NEWS
+++ b/NEWS
@@ -1,4 +1,4 @@
-GNU C Library NEWS -- history of user-visible changes.  2010-8-25
+GNU C Library NEWS -- history of user-visible changes.  2010-8-27
 Copyright (C) 1992-2009, 2010 Free Software Foundation, Inc.
 See the end for copying conditions.
 
@@ -11,6 +11,8 @@ Version 2.13
 
   10851, 11640, 11701, 11840, 11856, 11883, 11903, 11904
 
+* New interface: posix_spawn_file_actions_addchdir_np
+
 * New Linux interfaces: prlimit, prlimit64, fanotify_init, fanotify_mark
 
 * POWER7 optimizations: memset, memcmp, strncmp
diff --git a/posix/Makefile b/posix/Makefile
index 4f29963..4c21704 100644
--- a/posix/Makefile
+++ b/posix/Makefile
@@ -58,7 +58,7 @@ routines :=								      \
 	getaddrinfo gai_strerror wordexp				      \
 	pread pwrite pread64 pwrite64					      \
 	spawn_faction_init spawn_faction_destroy spawn_faction_addclose	      \
-	spawn_faction_addopen spawn_faction_adddup2			      \
+	spawn_faction_addopen spawn_faction_adddup2 spawn_faction_addchdir    \
 	spawnattr_init spawnattr_destroy				      \
 	spawnattr_getdefault spawnattr_setdefault			      \
 	spawnattr_getflags spawnattr_setflags				      \
diff --git a/posix/Versions b/posix/Versions
index 686c446..5f52bba 100644
--- a/posix/Versions
+++ b/posix/Versions
@@ -134,6 +134,9 @@ libc {
   GLIBC_2.11 {
     execvpe;
   }
+  GLIBC_2.13 {
+    posix_spawn_file_actions_addchdir_np;
+  }
   GLIBC_PRIVATE {
     __libc_fork; __libc_pwrite;
   }
diff --git a/posix/spawn.h b/posix/spawn.h
index 85ac69b..6edebd8 100644
--- a/posix/spawn.h
+++ b/posix/spawn.h
@@ -185,6 +185,14 @@ extern int posix_spawn_file_actions_adddup2 (posix_spawn_file_actions_t *
 					     __file_actions,
 					     int __fd, int __newfd) __THROW;
 
+#ifdef __USE_GNU
+/* Add an action to FILE-ACTIONS which tells the implementation to call
+   `fchdir' for the given file descriptors during the `spawn' call.  */
+extern int posix_spawn_file_actions_addchdir_np (posix_spawn_file_actions_t *
+						 __file_actions, int __fd)
+     __THROW;
+#endif
+
 __END_DECLS
 
 #endif /* spawn.h */
diff --git a/posix/spawn_faction_addclose.c b/posix/spawn_faction_addchdir.c
similarity index 86%
copy from posix/spawn_faction_addclose.c
copy to posix/spawn_faction_addchdir.c
index 69ce917..f8736cf 100644
--- a/posix/spawn_faction_addclose.c
+++ b/posix/spawn_faction_addchdir.c
@@ -1,4 +1,4 @@
-/* Copyright (C) 2000 Free Software Foundation, Inc.
+/* Copyright (C) 2010 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -23,9 +23,9 @@
 #include "spawn_int.h"
 
 /* Add an action to FILE-ACTIONS which tells the implementation to call
-   `close' for the given file descriptor during the `spawn' call.  */
+   `fchdir' for the given file descriptor during the `spawn' call.  */
 int
-posix_spawn_file_actions_addclose (posix_spawn_file_actions_t *file_actions,
+posix_spawn_file_actions_addchdir (posix_spawn_file_actions_t *file_actions,
 				   int fd)
 {
   int maxfd = __sysconf (_SC_OPEN_MAX);
@@ -43,8 +43,8 @@ posix_spawn_file_actions_addclose (posix_spawn_file_actions_t *file_actions,
 
   /* Add the new value.  */
   rec = &file_actions->__actions[file_actions->__used];
-  rec->tag = spawn_do_close;
-  rec->action.close_action.fd = fd;
+  rec->tag = spawn_do_chdir;
+  rec->action.chdir_action.fd = fd;
 
   /* Account for the new entry.  */
   ++file_actions->__used;
diff --git a/posix/spawn_int.h b/posix/spawn_int.h
index a3e9347..2dd05a1 100644
--- a/posix/spawn_int.h
+++ b/posix/spawn_int.h
@@ -5,7 +5,8 @@ struct __spawn_action
   {
     spawn_do_close,
     spawn_do_dup2,
-    spawn_do_open
+    spawn_do_open,
+    spawn_do_chdir
   } tag;
 
   union
@@ -26,6 +27,10 @@ struct __spawn_action
       int oflag;
       mode_t mode;
     } open_action;
+    struct
+    {
+      int fd;
+    } chdir_action;
   } action;
 };
 
diff --git a/sysdeps/posix/spawni.c b/sysdeps/posix/spawni.c
index 29803a8..c7993ee 100644
--- a/sysdeps/posix/spawni.c
+++ b/sysdeps/posix/spawni.c
@@ -210,6 +210,12 @@ __spawni (pid_t *pid, const char *file,
 		/* The `dup2' call failed.  */
 		_exit (SPAWN_ERROR);
 	      break;
+
+	    case spawn_do_chdir:
+	      if (__fchdir (action->action.chdir_action.fd))
+		/* The `fchdir' call failed.  */
+		_exit (SPAWN_ERROR);
+	      break;
 	    }
 	}
     }
-- 
1.7.2.2