osutil: implement setprocname to set process title for some platforms

This patch adds a simple setprocname method to osutil. The operation is not
defined by any standard and is platform-specific, the current implementation
tries to cover some major platforms (ex. Linux, OS X, FreeBSD) that is
relatively easy to support. Other platforms (Windows [4], other BSDs, ...)
can be added in the future.

The current implementation supports two methods to change process title:
  a. setproctitle if available (works in FreeBSD).
  b. rewrite argv in place (works in Linux [1] and Mac OS X). [2] [3]

[1]: Linux has "prctl(PR_SET_NAME, ...)" but 1) it has 16-byte limit, which
is too small; 2) it is not quite equivalent to what we want - it changes
"/proc/self/comm", not "/proc/self/cmdline" - "comm" change won't show up
in "ps" output unless "-o comm" is used.

[2]: The implementation does not rewrite the **environ buffer like some
other implementations do, just to make the code simpler and safer. However,
this also means the buffer size we can rewrite is significantly shorter. If
we are really greedy and want the "environ" space, we can change the
implementation later.

[3]: It requires a CPython private API: Py_GetArgcArgv to get the original
argv. Unfortunately Python 3 makes a copy of argv and returns the wchar_t
version, so it is not supported for now. (if we really want to, we could
count backwards from "char **environ", given known argc and argv, not sure
if that's a good idea - probably not)

[4]: The feature is aimed to make it easier for forked command server
processes to show what they are doing. Since Windows does not support
fork(), despite it's a major platform, its support is not added in this
patch.

mercurial/osutil.c

@@ -1,936 +1,997 b''
 /*
  osutil.c - native operating system services
 
  Copyright 2007 Matt Mackall and others
 
  This software may be used and distributed according to the terms of
  the GNU General Public License, incorporated herein by reference.
 */
 
 #define _ATFILE_SOURCE
 #include <Python.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <errno.h>
 
 #ifdef _WIN32
 #include <windows.h>
 #include <io.h>
 #else
 #include <dirent.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
 #endif
 
 #ifdef __APPLE__
 #include <sys/attr.h>
 #include <sys/vnode.h>
 #endif
 
 #include "util.h"
 
 /* some platforms lack the PATH_MAX definition (eg. GNU/Hurd) */
 #ifndef PATH_MAX
 #define PATH_MAX 4096
 #endif
 
 #ifdef _WIN32
 /*
 stat struct compatible with hg expectations
 Mercurial only uses st_mode, st_size and st_mtime
 the rest is kept to minimize changes between implementations
 */
 struct hg_stat {
 	int st_dev;
 	int st_mode;
 	int st_nlink;
 	__int64 st_size;
 	int st_mtime;
 	int st_ctime;
 };
 struct listdir_stat {
 	PyObject_HEAD
 	struct hg_stat st;
 };
 #else
 struct listdir_stat {
 	PyObject_HEAD
 	struct stat st;
 };
 #endif
 
 #ifdef IS_PY3K
 #define listdir_slot(name) \
 	static PyObject *listdir_stat_##name(PyObject *self, void *x) \
 	{ \
 		return PyLong_FromLong(((struct listdir_stat *)self)->st.name); \
 	}
 #else
 #define listdir_slot(name) \
 	static PyObject *listdir_stat_##name(PyObject *self, void *x) \
 	{ \
 		return PyInt_FromLong(((struct listdir_stat *)self)->st.name); \
 	}
 #endif
 
 listdir_slot(st_dev)
 listdir_slot(st_mode)
 listdir_slot(st_nlink)
 #ifdef _WIN32
 static PyObject *listdir_stat_st_size(PyObject *self, void *x)
 {
 	return PyLong_FromLongLong(
 		(PY_LONG_LONG)((struct listdir_stat *)self)->st.st_size);
 }
 #else
 listdir_slot(st_size)
 #endif
 listdir_slot(st_mtime)
 listdir_slot(st_ctime)
 
 static struct PyGetSetDef listdir_stat_getsets[] = {
 	{"st_dev", listdir_stat_st_dev, 0, 0, 0},
 	{"st_mode", listdir_stat_st_mode, 0, 0, 0},
 	{"st_nlink", listdir_stat_st_nlink, 0, 0, 0},
 	{"st_size", listdir_stat_st_size, 0, 0, 0},
 	{"st_mtime", listdir_stat_st_mtime, 0, 0, 0},
 	{"st_ctime", listdir_stat_st_ctime, 0, 0, 0},
 	{0, 0, 0, 0, 0}
 };
 
 static PyObject *listdir_stat_new(PyTypeObject *t, PyObject *a, PyObject *k)
 {
 	return t->tp_alloc(t, 0);
 }
 
 static void listdir_stat_dealloc(PyObject *o)
 {
 	o->ob_type->tp_free(o);
 }
 
 static PyTypeObject listdir_stat_type = {
 	PyVarObject_HEAD_INIT(NULL, 0)
 	"osutil.stat",             /*tp_name*/
 	sizeof(struct listdir_stat), /*tp_basicsize*/
 	0,                         /*tp_itemsize*/
 	(destructor)listdir_stat_dealloc, /*tp_dealloc*/
 	0,                         /*tp_print*/
 	0,                         /*tp_getattr*/
 	0,                         /*tp_setattr*/
 	0,                         /*tp_compare*/
 	0,                         /*tp_repr*/
 	0,                         /*tp_as_number*/
 	0,                         /*tp_as_sequence*/
 	0,                         /*tp_as_mapping*/
 	0,                         /*tp_hash */
 	0,                         /*tp_call*/
 	0,                         /*tp_str*/
 	0,                         /*tp_getattro*/
 	0,                         /*tp_setattro*/
 	0,                         /*tp_as_buffer*/
 	Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/
 	"stat objects",            /* tp_doc */
 	0,                         /* tp_traverse */
 	0,                         /* tp_clear */
 	0,                         /* tp_richcompare */
 	0,                         /* tp_weaklistoffset */
 	0,                         /* tp_iter */
 	0,                         /* tp_iternext */
 	0,                         /* tp_methods */
 	0,                         /* tp_members */
 	listdir_stat_getsets,      /* tp_getset */
 	0,                         /* tp_base */
 	0,                         /* tp_dict */
 	0,                         /* tp_descr_get */
 	0,                         /* tp_descr_set */
 	0,                         /* tp_dictoffset */
 	0,                         /* tp_init */
 	0,                         /* tp_alloc */
 	listdir_stat_new,          /* tp_new */
 };
 
 #ifdef _WIN32
 
 static int to_python_time(const FILETIME *tm)
 {
 	/* number of seconds between epoch and January 1 1601 */
 	const __int64 a0 = (__int64)134774L * (__int64)24L * (__int64)3600L;
 	/* conversion factor from 100ns to 1s */
 	const __int64 a1 = 10000000;
 	/* explicit (int) cast to suspend compiler warnings */
 	return (int)((((__int64)tm->dwHighDateTime << 32)
 			+ tm->dwLowDateTime) / a1 - a0);
 }
 
 static PyObject *make_item(const WIN32_FIND_DATAA *fd, int wantstat)
 {
 	PyObject *py_st;
 	struct hg_stat *stp;
 
 	int kind = (fd->dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY)
 		? _S_IFDIR : _S_IFREG;
 
 	if (!wantstat)
 		return Py_BuildValue("si", fd->cFileName, kind);
 
 	py_st = PyObject_CallObject((PyObject *)&listdir_stat_type, NULL);
 	if (!py_st)
 		return NULL;
 
 	stp = &((struct listdir_stat *)py_st)->st;
 	/*
 	use kind as st_mode
 	rwx bits on Win32 are meaningless
 	and Hg does not use them anyway
 	*/
 	stp->st_mode  = kind;
 	stp->st_mtime = to_python_time(&fd->ftLastWriteTime);
 	stp->st_ctime = to_python_time(&fd->ftCreationTime);
 	if (kind == _S_IFREG)
 		stp->st_size = ((__int64)fd->nFileSizeHigh << 32)
 				+ fd->nFileSizeLow;
 	return Py_BuildValue("siN", fd->cFileName,
 		kind, py_st);
 }
 
 static PyObject *_listdir(char *path, int plen, int wantstat, char *skip)
 {
 	PyObject *rval = NULL; /* initialize - return value */
 	PyObject *list;
 	HANDLE fh;
 	WIN32_FIND_DATAA fd;
 	char *pattern;
 
 	/* build the path + \* pattern string */
 	pattern = malloc(plen + 3); /* path + \* + \0 */
 	if (!pattern) {
 		PyErr_NoMemory();
 		goto error_nomem;
 	}
 	memcpy(pattern, path, plen);
 
 	if (plen > 0) {
 		char c = path[plen-1];
 		if (c != ':' && c != '/' && c != '\\')
 			pattern[plen++] = '\\';
 	}
 	pattern[plen++] = '*';
 	pattern[plen] = '\0';
 
 	fh = FindFirstFileA(pattern, &fd);
 	if (fh == INVALID_HANDLE_VALUE) {
 		PyErr_SetFromWindowsErrWithFilename(GetLastError(), path);
 		goto error_file;
 	}
 
 	list = PyList_New(0);
 	if (!list)
 		goto error_list;
 
 	do {
 		PyObject *item;
 
 		if (fd.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) {
 			if (!strcmp(fd.cFileName, ".")
 			|| !strcmp(fd.cFileName, ".."))
 				continue;
 
 			if (skip && !strcmp(fd.cFileName, skip)) {
 				rval = PyList_New(0);
 				goto error;
 			}
 		}
 
 		item = make_item(&fd, wantstat);
 		if (!item)
 			goto error;
 
 		if (PyList_Append(list, item)) {
 			Py_XDECREF(item);
 			goto error;
 		}
 
 		Py_XDECREF(item);
 	} while (FindNextFileA(fh, &fd));
 
 	if (GetLastError() != ERROR_NO_MORE_FILES) {
 		PyErr_SetFromWindowsErrWithFilename(GetLastError(), path);
 		goto error;
 	}
 
 	rval = list;
 	Py_XINCREF(rval);
 error:
 	Py_XDECREF(list);
 error_list:
 	FindClose(fh);
 error_file:
 	free(pattern);
 error_nomem:
 	return rval;
 }
 
 #else
 
 int entkind(struct dirent *ent)
 {
 #ifdef DT_REG
 	switch (ent->d_type) {
 	case DT_REG: return S_IFREG;
 	case DT_DIR: return S_IFDIR;
 	case DT_LNK: return S_IFLNK;
 	case DT_BLK: return S_IFBLK;
 	case DT_CHR: return S_IFCHR;
 	case DT_FIFO: return S_IFIFO;
 	case DT_SOCK: return S_IFSOCK;
 	}
 #endif
 	return -1;
 }
 
 static PyObject *makestat(const struct stat *st)
 {
 	PyObject *stat;
 
 	stat = PyObject_CallObject((PyObject *)&listdir_stat_type, NULL);
 	if (stat)
 		memcpy(&((struct listdir_stat *)stat)->st, st, sizeof(*st));
 	return stat;
 }
 
 static PyObject *_listdir_stat(char *path, int pathlen, int keepstat,
 			       char *skip)
 {
 	PyObject *list, *elem, *stat = NULL, *ret = NULL;
 	char fullpath[PATH_MAX + 10];
 	int kind, err;
 	struct stat st;
 	struct dirent *ent;
 	DIR *dir;
 #ifdef AT_SYMLINK_NOFOLLOW
 	int dfd = -1;
 #endif
 
 	if (pathlen >= PATH_MAX) {
 		errno = ENAMETOOLONG;
 		PyErr_SetFromErrnoWithFilename(PyExc_OSError, path);
 		goto error_value;
 	}
 	strncpy(fullpath, path, PATH_MAX);
 	fullpath[pathlen] = '/';
 
 #ifdef AT_SYMLINK_NOFOLLOW
 	dfd = open(path, O_RDONLY);
 	if (dfd == -1) {
 		PyErr_SetFromErrnoWithFilename(PyExc_OSError, path);
 		goto error_value;
 	}
 	dir = fdopendir(dfd);
 #else
 	dir = opendir(path);
 #endif
 	if (!dir) {
 		PyErr_SetFromErrnoWithFilename(PyExc_OSError, path);
 		goto error_dir;
 	}
 
 	list = PyList_New(0);
 	if (!list)
 		goto error_list;
 
 	while ((ent = readdir(dir))) {
 		if (!strcmp(ent->d_name, ".") || !strcmp(ent->d_name, ".."))
 			continue;
 
 		kind = entkind(ent);
 		if (kind == -1 || keepstat) {
 #ifdef AT_SYMLINK_NOFOLLOW
 			err = fstatat(dfd, ent->d_name, &st,
 				      AT_SYMLINK_NOFOLLOW);
 #else
 			strncpy(fullpath + pathlen + 1, ent->d_name,
 				PATH_MAX - pathlen);
 			fullpath[PATH_MAX] = '\0';
 			err = lstat(fullpath, &st);
 #endif
 			if (err == -1) {
 				/* race with file deletion? */
 				if (errno == ENOENT)
 					continue;
 				strncpy(fullpath + pathlen + 1, ent->d_name,
 					PATH_MAX - pathlen);
 				fullpath[PATH_MAX] = 0;
 				PyErr_SetFromErrnoWithFilename(PyExc_OSError,
 							       fullpath);
 				goto error;
 			}
 			kind = st.st_mode & S_IFMT;
 		}
 
 		/* quit early? */
 		if (skip && kind == S_IFDIR && !strcmp(ent->d_name, skip)) {
 			ret = PyList_New(0);
 			goto error;
 		}
 
 		if (keepstat) {
 			stat = makestat(&st);
 			if (!stat)
 				goto error;
 			elem = Py_BuildValue("siN", ent->d_name, kind, stat);
 		} else
 			elem = Py_BuildValue("si", ent->d_name, kind);
 		if (!elem)
 			goto error;
 		stat = NULL;
 
 		PyList_Append(list, elem);
 		Py_DECREF(elem);
 	}
 
 	ret = list;
 	Py_INCREF(ret);
 
 error:
 	Py_DECREF(list);
 	Py_XDECREF(stat);
 error_list:
 	closedir(dir);
 error_dir:
 #ifdef AT_SYMLINK_NOFOLLOW
 	close(dfd);
 #endif
 error_value:
 	return ret;
 }
 
 #ifdef __APPLE__
 
 typedef struct {
 	u_int32_t length;
 	attrreference_t name;
 	fsobj_type_t obj_type;
 	struct timespec mtime;
 #if __LITTLE_ENDIAN__
 	mode_t access_mask;
 	uint16_t padding;
 #else
 	uint16_t padding;
 	mode_t access_mask;
 #endif
 	off_t size;
 } __attribute__((packed)) attrbuf_entry;
 
 int attrkind(attrbuf_entry *entry)
 {
 	switch (entry->obj_type) {
 	case VREG: return S_IFREG;
 	case VDIR: return S_IFDIR;
 	case VLNK: return S_IFLNK;
 	case VBLK: return S_IFBLK;
 	case VCHR: return S_IFCHR;
 	case VFIFO: return S_IFIFO;
 	case VSOCK: return S_IFSOCK;
 	}
 	return -1;
 }
 
 /* get these many entries at a time */
 #define LISTDIR_BATCH_SIZE 50
 
 static PyObject *_listdir_batch(char *path, int pathlen, int keepstat,
 				char *skip, bool *fallback)
 {
 	PyObject *list, *elem, *stat = NULL, *ret = NULL;
 	int kind, err;
 	unsigned long index;
 	unsigned int count, old_state, new_state;
 	bool state_seen = false;
 	attrbuf_entry *entry;
 	/* from the getattrlist(2) man page: a path can be no longer than
 	   (NAME_MAX * 3 + 1) bytes. Also, "The getattrlist() function will
 	   silently truncate attribute data if attrBufSize is too small." So
 	   pass in a buffer big enough for the worst case. */
 	char attrbuf[LISTDIR_BATCH_SIZE * (sizeof(attrbuf_entry) + NAME_MAX * 3 + 1)];
 	unsigned int basep_unused;
 
 	struct stat st;
 	int dfd = -1;
 
 	/* these must match the attrbuf_entry struct, otherwise you'll end up
 	   with garbage */
 	struct attrlist requested_attr = {0};
 	requested_attr.bitmapcount = ATTR_BIT_MAP_COUNT;
 	requested_attr.commonattr = (ATTR_CMN_NAME | ATTR_CMN_OBJTYPE |
 				     ATTR_CMN_MODTIME | ATTR_CMN_ACCESSMASK);
 	requested_attr.fileattr = ATTR_FILE_DATALENGTH;
 
 	*fallback = false;
 
 	if (pathlen >= PATH_MAX) {
 		errno = ENAMETOOLONG;
 		PyErr_SetFromErrnoWithFilename(PyExc_OSError, path);
 		goto error_value;
 	}
 
 	dfd = open(path, O_RDONLY);
 	if (dfd == -1) {
 		PyErr_SetFromErrnoWithFilename(PyExc_OSError, path);
 		goto error_value;
 	}
 
 	list = PyList_New(0);
 	if (!list)
 		goto error_dir;
 
 	do {
 		count = LISTDIR_BATCH_SIZE;
 		err = getdirentriesattr(dfd, &requested_attr, &attrbuf,
 					sizeof(attrbuf), &count, &basep_unused,
 					&new_state, 0);
 		if (err < 0) {
 			if (errno == ENOTSUP) {
 				/* We're on a filesystem that doesn't support
 				   getdirentriesattr. Fall back to the
 				   stat-based implementation. */
 				*fallback = true;
 			} else
 				PyErr_SetFromErrnoWithFilename(PyExc_OSError, path);
 			goto error;
 		}
 
 		if (!state_seen) {
 			old_state = new_state;
 			state_seen = true;
 		} else if (old_state != new_state) {
 			/* There's an edge case with getdirentriesattr. Consider
 			   the following initial list of files:
 
 			   a
 			   b
 			   <--
 			   c
 			   d
 
 			   If the iteration is paused at the arrow, and b is
 			   deleted before it is resumed, getdirentriesattr will
 			   not return d at all!  Ordinarily we're expected to
 			   restart the iteration from the beginning. To avoid
 			   getting stuck in a retry loop here, fall back to
 			   stat. */
 			*fallback = true;
 			goto error;
 		}
 
 		entry = (attrbuf_entry *)attrbuf;
 
 		for (index = 0; index < count; index++) {
 			char *filename = ((char *)&entry->name) +
 				entry->name.attr_dataoffset;
 
 			if (!strcmp(filename, ".") || !strcmp(filename, ".."))
 				continue;
 
 			kind = attrkind(entry);
 			if (kind == -1) {
 				PyErr_Format(PyExc_OSError,
 					     "unknown object type %u for file "
 					     "%s%s!",
 					     entry->obj_type, path, filename);
 				goto error;
 			}
 
 			/* quit early? */
 			if (skip && kind == S_IFDIR && !strcmp(filename, skip)) {
 				ret = PyList_New(0);
 				goto error;
 			}
 
 			if (keepstat) {
 				/* from the getattrlist(2) man page: "Only the
 				   permission bits ... are valid". */
 				st.st_mode = (entry->access_mask & ~S_IFMT) | kind;
 				st.st_mtime = entry->mtime.tv_sec;
 				st.st_size = entry->size;
 				stat = makestat(&st);
 				if (!stat)
 					goto error;
 				elem = Py_BuildValue("siN", filename, kind, stat);
 			} else
 				elem = Py_BuildValue("si", filename, kind);
 			if (!elem)
 				goto error;
 			stat = NULL;
 
 			PyList_Append(list, elem);
 			Py_DECREF(elem);
 
 			entry = (attrbuf_entry *)((char *)entry + entry->length);
 		}
 	} while (err == 0);
 
 	ret = list;
 	Py_INCREF(ret);
 
 error:
 	Py_DECREF(list);
 	Py_XDECREF(stat);
 error_dir:
 	close(dfd);
 error_value:
 	return ret;
 }
 
 #endif /* __APPLE__ */
 
 static PyObject *_listdir(char *path, int pathlen, int keepstat, char *skip)
 {
 #ifdef __APPLE__
 	PyObject *ret;
 	bool fallback = false;
 
 	ret = _listdir_batch(path, pathlen, keepstat, skip, &fallback);
 	if (ret != NULL || !fallback)
 		return ret;
 #endif
 	return _listdir_stat(path, pathlen, keepstat, skip);
 }
 
 static PyObject *statfiles(PyObject *self, PyObject *args)
 {
 	PyObject *names, *stats;
 	Py_ssize_t i, count;
 
 	if (!PyArg_ParseTuple(args, "O:statfiles", &names))
 		return NULL;
 
 	count = PySequence_Length(names);
 	if (count == -1) {
 		PyErr_SetString(PyExc_TypeError, "not a sequence");
 		return NULL;
 	}
 
 	stats = PyList_New(count);
 	if (stats == NULL)
 		return NULL;
 
 	for (i = 0; i < count; i++) {
 		PyObject *stat, *pypath;
 		struct stat st;
 		int ret, kind;
 		char *path;
 
 		/* With a large file count or on a slow filesystem,
 		   don't block signals for long (issue4878). */
 		if ((i % 1000) == 999 && PyErr_CheckSignals() == -1)
 			goto bail;
 
 		pypath = PySequence_GetItem(names, i);
 		if (!pypath)
 			goto bail;
 		path = PyBytes_AsString(pypath);
 		if (path == NULL) {
 			Py_DECREF(pypath);
 			PyErr_SetString(PyExc_TypeError, "not a string");
 			goto bail;
 		}
 		ret = lstat(path, &st);
 		Py_DECREF(pypath);
 		kind = st.st_mode & S_IFMT;
 		if (ret != -1 && (kind == S_IFREG || kind == S_IFLNK)) {
 			stat = makestat(&st);
 			if (stat == NULL)
 				goto bail;
 			PyList_SET_ITEM(stats, i, stat);
 		} else {
 			Py_INCREF(Py_None);
 			PyList_SET_ITEM(stats, i, Py_None);
 		}
 	}
 
 	return stats;
 
 bail:
 	Py_DECREF(stats);
 	return NULL;
 }
 
 /*
  * recvfds() simply does not release GIL during blocking io operation because
  * command server is known to be single-threaded.
  *
  * Old systems such as Solaris don't provide CMSG_LEN, msg_control, etc.
  * Currently, recvfds() is not supported on these platforms.
  */
 #ifdef CMSG_LEN
 
 static ssize_t recvfdstobuf(int sockfd, int **rfds, void *cbuf, size_t cbufsize)
 {
 	char dummy[1];
 	struct iovec iov = {dummy, sizeof(dummy)};
 	struct msghdr msgh = {0};
 	struct cmsghdr *cmsg;
 
 	msgh.msg_iov = &iov;
 	msgh.msg_iovlen = 1;
 	msgh.msg_control = cbuf;
 	msgh.msg_controllen = (socklen_t)cbufsize;
 	if (recvmsg(sockfd, &msgh, 0) < 0)
 		return -1;
 
 	for (cmsg = CMSG_FIRSTHDR(&msgh); cmsg;
 	     cmsg = CMSG_NXTHDR(&msgh, cmsg)) {
 		if (cmsg->cmsg_level != SOL_SOCKET ||
 		    cmsg->cmsg_type != SCM_RIGHTS)
 			continue;
 		*rfds = (int *)CMSG_DATA(cmsg);
 		return (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
 	}
 
 	*rfds = cbuf;
 	return 0;
 }
 
 static PyObject *recvfds(PyObject *self, PyObject *args)
 {
 	int sockfd;
 	int *rfds = NULL;
 	ssize_t rfdscount, i;
 	char cbuf[256];
 	PyObject *rfdslist = NULL;
 
 	if (!PyArg_ParseTuple(args, "i", &sockfd))
 		return NULL;
 
 	rfdscount = recvfdstobuf(sockfd, &rfds, cbuf, sizeof(cbuf));
 	if (rfdscount < 0)
 		return PyErr_SetFromErrno(PyExc_OSError);
 
 	rfdslist = PyList_New(rfdscount);
 	if (!rfdslist)
 		goto bail;
 	for (i = 0; i < rfdscount; i++) {
 		PyObject *obj = PyLong_FromLong(rfds[i]);
 		if (!obj)
 			goto bail;
 		PyList_SET_ITEM(rfdslist, i, obj);
 	}
 	return rfdslist;
 
 bail:
 	Py_XDECREF(rfdslist);
 	return NULL;
 }
 
 #endif /* CMSG_LEN */
+
+#if defined(HAVE_SETPROCTITLE)
+/* setproctitle is the first choice - available in FreeBSD */
+#define SETPROCNAME_USE_SETPROCTITLE
+#elif (defined(__linux__) || defined(__APPLE__)) && PY_MAJOR_VERSION == 2
+/* rewrite the argv buffer in place - works in Linux and OS X. Py_GetArgcArgv
+ * in Python 3 returns the copied wchar_t **argv, thus unsupported. */
+#define SETPROCNAME_USE_ARGVREWRITE
+#else
+#define SETPROCNAME_USE_NONE
+#endif
+
+#ifndef SETPROCNAME_USE_NONE
+static PyObject *setprocname(PyObject *self, PyObject *args)
+{
+	const char *name = NULL;
+	if (!PyArg_ParseTuple(args, "s", &name))
+		return NULL;
+
+#if defined(SETPROCNAME_USE_SETPROCTITLE)
+	setproctitle("%s", name);
+#elif defined(SETPROCNAME_USE_ARGVREWRITE)
+	{
+		static char *argvstart = NULL;
+		static size_t argvsize = 0;
+		if (argvstart == NULL) {
+			int argc = 0, i;
+			char **argv = NULL;
+			char *argvend;
+			extern void Py_GetArgcArgv(int *argc, char ***argv);
+			Py_GetArgcArgv(&argc, &argv);
+
+			/* Check the memory we can use. Typically, argv[i] and
+			 * argv[i + 1] are continuous. */
+			argvend = argvstart = argv[0];
+			for (i = 0; i < argc; ++i) {
+				if (argv[i] > argvend || argv[i] < argvstart)
+					break; /* not continuous */
+				size_t len = strlen(argv[i]);
+				argvend = argv[i] + len + 1 /* '\0' */;
+			}
+			if (argvend > argvstart) /* sanity check */
+				argvsize = argvend - argvstart;
+		}
+
+		if (argvstart && argvsize > 1) {
+			int n = snprintf(argvstart, argvsize, "%s", name);
+			if (n >= 0 && (size_t)n < argvsize)
+				memset(argvstart + n, 0, argvsize - n);
+		}
+	}
+#endif
+
+	Py_RETURN_NONE;
+}
+#endif /* ndef SETPROCNAME_USE_NONE */
+
 #endif /* ndef _WIN32 */
 
 static PyObject *listdir(PyObject *self, PyObject *args, PyObject *kwargs)
 {
 	PyObject *statobj = NULL; /* initialize - optional arg */
 	PyObject *skipobj = NULL; /* initialize - optional arg */
 	char *path, *skip = NULL;
 	int wantstat, plen;
 
 	static char *kwlist[] = {"path", "stat", "skip", NULL};
 
 	if (!PyArg_ParseTupleAndKeywords(args, kwargs, "s#|OO:listdir",
 			kwlist, &path, &plen, &statobj, &skipobj))
 		return NULL;
 
 	wantstat = statobj && PyObject_IsTrue(statobj);
 
 	if (skipobj && skipobj != Py_None) {
 		skip = PyBytes_AsString(skipobj);
 		if (!skip)
 			return NULL;
 	}
 
 	return _listdir(path, plen, wantstat, skip);
 }
 
 #ifdef _WIN32
 static PyObject *posixfile(PyObject *self, PyObject *args, PyObject *kwds)
 {
 	static char *kwlist[] = {"name", "mode", "buffering", NULL};
 	PyObject *file_obj = NULL;
 	char *name = NULL;
 	char *mode = "rb";
 	DWORD access = 0;
 	DWORD creation;
 	HANDLE handle;
 	int fd, flags = 0;
 	int bufsize = -1;
 	char m0, m1, m2;
 	char fpmode[4];
 	int fppos = 0;
 	int plus;
 	FILE *fp;
 
 	if (!PyArg_ParseTupleAndKeywords(args, kwds, "et|si:posixfile", kwlist,
 					 Py_FileSystemDefaultEncoding,
 					 &name, &mode, &bufsize))
 		return NULL;
 
 	m0 = mode[0];
 	m1 = m0 ? mode[1] : '\0';
 	m2 = m1 ? mode[2] : '\0';
 	plus = m1 == '+' || m2 == '+';
 
 	fpmode[fppos++] = m0;
 	if (m1 == 'b' || m2 == 'b') {
 		flags = _O_BINARY;
 		fpmode[fppos++] = 'b';
 	}
 	else
 		flags = _O_TEXT;
 	if (m0 == 'r' && !plus) {
 		flags |= _O_RDONLY;
 		access = GENERIC_READ;
 	} else {
 		/*
 		work around http://support.microsoft.com/kb/899149 and
 		set _O_RDWR for 'w' and 'a', even if mode has no '+'
 		*/
 		flags |= _O_RDWR;
 		access = GENERIC_READ | GENERIC_WRITE;
 		fpmode[fppos++] = '+';
 	}
 	fpmode[fppos++] = '\0';
 
 	switch (m0) {
 	case 'r':
 		creation = OPEN_EXISTING;
 		break;
 	case 'w':
 		creation = CREATE_ALWAYS;
 		break;
 	case 'a':
 		creation = OPEN_ALWAYS;
 		flags |= _O_APPEND;
 		break;
 	default:
 		PyErr_Format(PyExc_ValueError,
 			     "mode string must begin with one of 'r', 'w', "
 			     "or 'a', not '%c'", m0);
 		goto bail;
 	}
 
 	handle = CreateFile(name, access,
 			    FILE_SHARE_READ | FILE_SHARE_WRITE |
 			    FILE_SHARE_DELETE,
 			    NULL,
 			    creation,
 			    FILE_ATTRIBUTE_NORMAL,
 			    0);
 
 	if (handle == INVALID_HANDLE_VALUE) {
 		PyErr_SetFromWindowsErrWithFilename(GetLastError(), name);
 		goto bail;
 	}
 
 	fd = _open_osfhandle((intptr_t)handle, flags);
 
 	if (fd == -1) {
 		CloseHandle(handle);
 		PyErr_SetFromErrnoWithFilename(PyExc_IOError, name);
 		goto bail;
 	}
 #ifndef IS_PY3K
 	fp = _fdopen(fd, fpmode);
 	if (fp == NULL) {
 		_close(fd);
 		PyErr_SetFromErrnoWithFilename(PyExc_IOError, name);
 		goto bail;
 	}
 
 	file_obj = PyFile_FromFile(fp, name, mode, fclose);
 	if (file_obj == NULL) {
 		fclose(fp);
 		goto bail;
 	}
 
 	PyFile_SetBufSize(file_obj, bufsize);
 #else
 	file_obj = PyFile_FromFd(fd, name, mode, bufsize, NULL, NULL, NULL, 1);
 	if (file_obj == NULL)
 		goto bail;
 #endif
 bail:
 	PyMem_Free(name);
 	return file_obj;
 }
 #endif
 
 #ifdef __APPLE__
 #include <ApplicationServices/ApplicationServices.h>
 
 static PyObject *isgui(PyObject *self)
 {
 	CFDictionaryRef dict = CGSessionCopyCurrentDictionary();
 
 	if (dict != NULL) {
 		CFRelease(dict);
 		Py_RETURN_TRUE;
 	} else {
 		Py_RETURN_FALSE;
 	}
 }
 #endif
 
 static char osutil_doc[] = "Native operating system services.";
 
 static PyMethodDef methods[] = {
 	{"listdir", (PyCFunction)listdir, METH_VARARGS | METH_KEYWORDS,
 	 "list a directory\n"},
 #ifdef _WIN32
 	{"posixfile", (PyCFunction)posixfile, METH_VARARGS | METH_KEYWORDS,
 	 "Open a file with POSIX-like semantics.\n"
 "On error, this function may raise either a WindowsError or an IOError."},
 #else
 	{"statfiles", (PyCFunction)statfiles, METH_VARARGS | METH_KEYWORDS,
 	 "stat a series of files or symlinks\n"
 "Returns None for non-existent entries and entries of other types.\n"},
 #ifdef CMSG_LEN
 	{"recvfds", (PyCFunction)recvfds, METH_VARARGS,
 	 "receive list of file descriptors via socket\n"},
 #endif
+#ifndef SETPROCNAME_USE_NONE
+	{"setprocname", (PyCFunction)setprocname, METH_VARARGS,
+	 "set process title (best-effort)\n"},
 #endif
+#endif /* ndef _WIN32 */
 #ifdef __APPLE__
 	{
 		"isgui", (PyCFunction)isgui, METH_NOARGS,
 		"Is a CoreGraphics session available?"
 	},
 #endif
 	{NULL, NULL}
 };
 
 #ifdef IS_PY3K
 static struct PyModuleDef osutil_module = {
 	PyModuleDef_HEAD_INIT,
 	"osutil",
 	osutil_doc,
 	-1,
 	methods
 };
 
 PyMODINIT_FUNC PyInit_osutil(void)
 {
 	if (PyType_Ready(&listdir_stat_type) < 0)
 		return NULL;
 
 	return PyModule_Create(&osutil_module);
 }
 #else
 PyMODINIT_FUNC initosutil(void)
 {
 	if (PyType_Ready(&listdir_stat_type) == -1)
 		return;
 
 	Py_InitModule3("osutil", methods, osutil_doc);
 }
 #endif