lib/chkname.[ch]: login_name_max_size(): Add function, and add missing error handling

[alejandro-colomar]

It encapsulates some logic that we may want to reuse elsewhere.

Link: #989

Prompted by @MarcinDigitic's PR.

---

Revisions:

v2

• Call this function in a few places to add error handling.

$ git range-diff gh/master gh/loginnamemax loginnamemax 
1:  53067b08 = 1:  53067b08 lib/chkname.[ch]: Fix includes
2:  5c0af110 = 2:  5c0af110 lib/chkname.[ch]: login_name_max_size(): Add function
-:  -------- > 3:  2ac009ea src/login.c: main(): Use login_name_max_size()

v2b

• Add missing include

$ git range-diff gh/master gh/loginnamemax loginnamemax 
1:  53067b08 = 1:  53067b08 lib/chkname.[ch]: Fix includes
2:  5c0af110 = 2:  5c0af110 lib/chkname.[ch]: login_name_max_size(): Add function
3:  2ac009ea ! 3:  51709012 src/login.c: main(): Use login_name_max_size()
    @@ Commit message
         Signed-off-by: Alejandro Colomar <alx@kernel.org>
     
      ## src/login.c ##
    +@@
    + 
    + #include "alloc.h"
    + #include "attr.h"
    ++#include "chkname.h"
    + #include "defines.h"
    + #include "faillog.h"
    + #include "failure.h"
     @@ src/login.c: int main (int argc, char **argv)
        }
      #ifdef RLOGIN

[ikerexxe]

I think this is fine.

Alejandro do you want to tackle MarcinDigitic's comment in this PR?

[alejandro-colomar]

I think this is fine.

Thanks!

Alejandro do you want to tackle MarcinDigitic's comment in this PR?

Nah. I'll leave that for his PR. I left many comments there, and I guess that after we merge this he will be able to address them.