/etc/shadow and /etc/passwd I/O

[Valdir Leite]

Hi all,
 I´m studying PAM and now I´m facing a dilemma: I want to create a small 
program like "/bin/passwd", to allow one user to change his/her shadowed 
password or someone´s password based on pre-defined polices (Ok, I know it 
was already built, but I want to know the details abou PAM, GETPWNAM, etc).
 I have found source from shadow-utils, PAM, passwd, et cetera, and in 
almost all of them, the I/O handling is made by shadowio.c, passwdio.c or 
commonio.c, from "Julianne Frances Haugh" source.
 My questions are: 
Do I must get those files and compile them with my own source, or is there a 
lib or another way to use functions like spw_update, spw_lock to do the job 
?
 How is the "link" between a programa like mine (to allow a user to change 
your own password) and PAM ? For example, in Julianne's passwd.c there are a 
lot of "#ifndef USE_PAM" but, for what ? I didn't understand the context at 
all.
 I'm not sure that my questions are clear, but any help is welcome!
 Thanks in advance,
 Valdir Leite
Sao Paulo
Brasil
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