add posix_spawn [f]chdir file actions

these are presently extensions, thus named with _np to match glibc and
other implementations that provide them; however they are likely to be
standardized in the future without the _np suffix as a result of
Austin Group issue 1208. if so, both names will be kept as aliases.

include/spawn.h

@@ -71,6 +71,11 @@ int posix_spawn_file_actions_addopen(posix_spawn_file_actions_t *__restrict, int
 int posix_spawn_file_actions_addclose(posix_spawn_file_actions_t *, int);
 int posix_spawn_file_actions_adddup2(posix_spawn_file_actions_t *, int, int);
 
+#if defined(_BSD_SOURCE) || defined(_GNU_SOURCE)
+int posix_spawn_file_actions_addchdir_np(posix_spawn_file_actions_t *__restrict, const char *__restrict);
+int posix_spawn_file_actions_addfchdir_np(posix_spawn_file_actions_t *, int);
+#endif
+
 #ifdef __cplusplus
 }
 #endif

src/process/fdop.h

@@ -1,6 +1,8 @@
 #define FDOP_CLOSE 1
 #define FDOP_DUP2 2
 #define FDOP_OPEN 3
+#define FDOP_CHDIR 4
+#define FDOP_FCHDIR 5
 
 struct fdop {
 	struct fdop *next, *prev;

src/process/posix_spawn.c

@@ -125,6 +125,14 @@ static int child(void *args_vp)
 					__syscall(SYS_close, fd);
 				}
 				break;
+			case FDOP_CHDIR:
+				ret = __syscall(SYS_chdir, op->path);
+				if (ret<0) goto fail;
+				break;
+			case FDOP_FCHDIR:
+				ret = __syscall(SYS_fchdir, op->fd);
+				if (ret<0) goto fail;
+				break;
 			}
 		}
 	}

src/process/posix_spawn_file_actions_addchdir.c

@@ -0,0 +1,18 @@
+#include <spawn.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include "fdop.h"
+
+int posix_spawn_file_actions_addchdir_np(posix_spawn_file_actions_t *restrict fa, const char *restrict path)
+{
+	struct fdop *op = malloc(sizeof *op + strlen(path) + 1);
+	if (!op) return ENOMEM;
+	op->cmd = FDOP_CHDIR;
+	op->fd = -1;
+	strcpy(op->path, path);
+	if ((op->next = fa->__actions)) op->next->prev = op;
+	op->prev = 0;
+	fa->__actions = op;
+	return 0;
+}

src/process/posix_spawn_file_actions_addfchdir.c

@@ -0,0 +1,17 @@
+#include <spawn.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include "fdop.h"
+
+int posix_spawn_file_actions_addfchdir_np(posix_spawn_file_actions_t *fa, int fd)
+{
+	struct fdop *op = malloc(sizeof *op);
+	if (!op) return ENOMEM;
+	op->cmd = FDOP_FCHDIR;
+	op->fd = fd;
+	if ((op->next = fa->__actions)) op->next->prev = op;
+	op->prev = 0;
+	fa->__actions = op;
+	return 0;
+}