[Python-Dev] Add Py_off_t and related APIs?

[Victor Stinner]

Le Tuesday 13 January 2009 22:47:52 Victor Stinner, vous avez écrit :
> Le Tuesday 13 January 2009 21:33:28 Martin v. Löwis, vous avez écrit :
> > I would do this through a converter function (O&), but yes,
> > making it private to the io library sounds about right. Who
> > else would benefit from it?
>
> On Linux, mmap() prototype is (...)

A more complete answer... Current usage of off_t types in Python:

(1) mmap.mmap(): [use Py_ssize_t]

Use "Py_ssize_t i = PyNumber_AsSsize_t(o, PyExc_OverflowError)".

(2) posix.lseek(), posix.ftruncate(), fcnt.lockf(): [off_t, 
    struct flock for fcntl.lockf()]

Use PyInt_AsLong(posobj),
or "PyLong_Check(posobj)? PyLong_AsLongLong(posobj) : PyInt_AsLong(posobj)"
if HAVE_LARGEFILE_SUPPORT.

(3) posix.stat(): [struct win32_stat/struct stat]

use PyInt_FromLong(st->st_size),
or PyLong_FromLongLong((PY_LONG_LONG)st->st_size) if HAVE_LARGEFILE_SUPPORT

---

Using >>find /usr/include -name "*.h"|xargs grep -H off_t<< I found:
 - file operations:
   * lseek(), truncate(), fseeko(), ftello()
   * file size in the *stat() structure
   * (fcntl) lockf(), fadvice(), fallocate()
   * pread(), pwrite()
   * async I/O like aio_read()
 - dirent structure used by readir()
 - sendfile()
 - mmap()

Some libraries define their own offset type:
 - [gzip] z_off_t used by gzseek(), gztell() defined as a long
 - [mysql] my_off_t is unsigned long, or ulonglong size if sizeof(off_t) > 4,
   os_off_t is off_t
 - etc.

-- 
Victor Stinner aka haypo
http://www.haypocalc.com/blog/