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Date: Fri, 20 Feb 2004 20:14:41 +0100
From: Johannes Stezenbach <js@convergence.de>
To: Andries Brouwer <aebr@win.tue.nl>
Cc: James Simmons <jsimmons@infradead.org>, Greg KH <greg@kroah.com>,
       linux-hotplug-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org
Subject: Re: HOWTO use udev to manage /dev
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On Fri, Feb 20, 2004 at 01:52:37AM +0100, Andries Brouwer wrote:
> On Thu, Feb 19, 2004 at 08:21:25PM +0000, James Simmons wrote:
> 
> > Okay. If I change the major number of serial ttys inside the kernel 
> > of course udev would properly handle this. Now the question is would this 
> > break userland applications using the serial port?
> 
> Yes, a few of them.
> Ordinarily, userland software uses pathnames in /dev.
> But some software knows too much.
> 
> In dietlibc-0.20 one can read:
> 
> char *ttyname(int fd) {
> ...
>   if (S_ISCHR(s.st_mode)) {
>     n=minor(s.st_rdev);
>     switch (major(s.st_rdev)) {
>     case 4:
> ...
>     case 2:
> ...
>     case 136:
>     case 137:
>     case 138:
>     case 139:
> ...
> }
> 
> This code knows about the actual values of majors.
> There are lots of examples like this.

dietlibc actually uses readlink from /proc/sef/fd/. The code
you quote is used only if one #undef SLASH_PROC_OK in dietfeatures.h.
Few people will use this, and those that do probably have a
good reason.

Johannes