Description of Problem:

When having /usr mounted read-only and put into rpm's %_netsharedpath, the
%post scriplet of glibc fails at updating. This leads to an inconsistent
rpm database (two glibc's are installed).

Strace'ing the /usr/sbin/glibc_post_upgrade command says:

[pid 23439] open("/usr/lib/gconv/gconv-modules.cache",
O_RDWR|O_CREAT|O_TRUNC, 0644) = -1 EROFS (Read-only file system)
[pid 23439] _exit(1)                    = ?
<... wait4 resumed> [WIFEXITED(s) && WEXITSTATUS(s) == 1], 0, NULL) = 23439
--- SIGCHLD (Child exited) ---
_exit(1)                                = ?


How Reproducible:

everytime


Steps to Reproduce:
1. mount -o remount,ro
2. echo '%_netsharedpath /usr' >/etc/rpm/macros
3. rpm -U glibc-2.2.3-19.1
4. rpm -q glibc


Actual Results:

(3) execution of %post scriptlet from glibc-2.2.3-19.1 failed, exit status 1
(4) 
glibc-2.2.3-19
glibc-2.2.3-19.1


Expected Results:

(3) no message
(4) glibc-2.2.3-19.1


Additional Information:
	
tested with glibc-2.2.3-19.1 but happens with 2.2.3-19 also.