Re: What do you think?
At 10:00 +0800 1998-10-02, Mikolaj J. Habryn wrote:
[ snip stuff about chown/lchown ]
Just for reference, glibc 2.1 (for powerpc) has a fairly elegant solution
to the lchown/chown problem.
These files are from sysdeps/unix/sysv/linux/powerpc/ in the glibc 2.1 sources.
-- begin chown.c --
/* chown() compatibility.
Copyright (C) 1998 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
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If not,
write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <limits.h>
#include <sys/syscall.h>
#include <stdlib.h>
/*
In Linux 2.1.x the chown functions have been changed. A new function lchown
was introduced. The new chown now follows symlinks - the old chown and the
new lchown do not follow symlinks.
This file emulates chown() under the old kernels.
*/
extern int __syscall_chown (const char *__file,
uid_t __owner, gid_t __group);
int
__chown (const char *file, uid_t owner, gid_t group)
{
int err;
int old_errno;
char link[PATH_MAX+2];
char path[2*PATH_MAX+4];
int loopct;
int filelen;
static int libc_old_chown = 0 /* -1=old linux, 1=new linux, 0=unknown */;
if (libc_old_chown == 1)
return __syscall_chown (file, owner, group);
old_errno = errno;
#ifdef __NR_lchown
if (libc_old_chown == 0)
{
err = __syscall_chown (file, owner, group);
if (err != -1 || errno != ENOSYS)
{
libc_old_chown = 1;
return err;
}
libc_old_chown = -1;
}
#endif
err = __readlink (file, link, PATH_MAX+1);
if (err == -1)
{
errno = old_errno;
return __lchown(file, owner, group);
}
filelen = strlen (file) + 1;
if (filelen > sizeof(path))
{
errno = ENAMETOOLONG;
return -1;
}
memcpy (path, file, filelen);
/* 'The system has an arbitrary limit...' In practise, we'll hit
ENAMETOOLONG before this, usually. */
for (loopct = 0; loopct < 128; loopct++)
{
int linklen;
if (err >= PATH_MAX+1)
{
errno = ENAMETOOLONG;
return -1;
}
link[err] = 0; /* Null-terminate string, just-in-case. */
linklen = strlen (link) + 1;
if (link[0] == '/')
memcpy (path, link, linklen);
else
{
filelen = strlen (path);
while (filelen > 1 && path[filelen-1] == '/')
filelen--;
while (filelen > 0 && path[filelen-1] != '/')
filelen--;
if (filelen + linklen > sizeof(path))
{
errno = ENAMETOOLONG;
return -1;
}
memcpy (path+filelen, link, linklen);
}
err = __readlink(path, link, PATH_MAX+1);
if (err == -1)
{
errno = old_errno;
return __lchown(path, owner, group);
}
}
errno = ELOOP;
return -1;
}
#if defined PIC && defined DO_VERSIONING
default_symbol_version (__chown, chown, GLIBC_2.1);
#else
weak_alias (__chown, chown)
#endif
-- end chown.c --
-- begin lchown.S --
/* lchown system call.
Copyright (C) 1998 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
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If not,
write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
/* Some old kernel headers call lchown() 'chown'. The number is
the same. */
#include <sysdep.h>
#ifdef __NR_lchown
PSEUDO (__lchown, lchown, 3)
#else
PSEUDO (__lchown, chown, 3)
#endif
ret
PSEUDO_END(__lchown)
weak_alias (__lchown, lchown)
#if defined PIC && defined DO_VERSIONING
symbol_version (__lchown, chown, GLIBC_2.0);
#endif
-- end lchown.S --
There's also this entry in syscalls.list:
s_chown chown chown 3 __syscall_chown
--
Joel Klecker (aka Espy)
<URL:mailto:jk@espy.org> <URL:http://web.espy.org/>
Debian GNU/Linux user/developer on i386 and powerpc.
<URL:mailto:espy@debian.org> <URL:http://www.debian.org/>
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