[U-Boot-Users] [PATCH] Use `ln -sf` rather than `rm -f && ln -s`

[Wolfgang Denk]

In message <200801281557.55976.vapier at gentoo.org> you wrote:
>
> > > -		@rm -f $(obj)environment.c
> > > -		ln -s $(src)../common/environment.c $(obj)environment.c
> > > +		ln -s -f $(src)../common/environment.c $(obj)environment.c
> >
> > Be careful here. Are you 100% sure that all systems in the field will
> > behave exactly as your's is doing?
> 
> i really dont understand what you mean.  any POSIX compliant system will 
> behave exactly as it's supposed to: if the destination exists already, unlink 
> it just before creating the link.

I finally fund such a situation again.

# cat /proc/version 
Linux version 2.6.22.14-72.fc6 (brewbuilder at ls20-bc1-14.build.redhat.com) (gcc version 4.1.2 20070626 (Red Hat 4.1.2-13)) #1 SMP Wed Nov 21 14:10:25 EST 2007
# cat /etc/issue
Fedora Core release 6 (Zod)
Kernel \r on an \m

# id
uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel)
# cd /opt
# ls -ld eldk eldk-4.2-2008-03-27 eldk-4.2-2008-04-01
lrwxrwxrwx  1 root root   19 Apr  4 04:01 eldk -> eldk-4.2-2008-03-27
drwxr-xr-x 14 root root 4096 Apr  8 23:37 eldk-4.2-2008-03-27
drwxr-xr-x 14 root root 4096 Apr  3 13:38 eldk-4.2-2008-04-01


Now we try:

# ln -sf eldk-4.2-2008-04-01 eldk
# echo $?
0

And what do you think we got?

# ls -ld eldk eldk-4.2-2008-03-27 eldk-4.2-2008-04-01
lrwxrwxrwx  1 root root   19 Apr  4 04:01 eldk -> eldk-4.2-2008-03-27
drwxr-xr-x 14 root root 4096 Apr 14 21:27 eldk-4.2-2008-03-27
drwxr-xr-x 14 root root 4096 Apr  3 13:38 eldk-4.2-2008-04-01


This is what I mean when I say that "rm -f foo ; ln -s bar foo" is
*NOT* exactly equivalent to "ln -sf bar foo". The former will always
work, the latter won't.

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
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