Simplify is_my_tty()

This commit will serve to document why we shouldn't worry about the
truncation in the call to strlcpy(3).  Since we have one more byte in
tmptty than in full_tty, truncation will produce a string that is at
least one byte longer than full_tty.  Such a string could never compare
equal, so we're actually handling the truncation in a clever way.  Maybe
too clever, but that's why I'm documenting it here.

Now, about the simplification itself:

Since we made sure that both full_tty and tmptty are null-terminated, we
can call strcmp(3) instead of strncmp(3).  We can also simplify the
return logic avoiding one branch.

Cc: Paul Eggert <eggert@cs.ucla.edu>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
Reviewed-by: Iker Pedrosa <ipedrosa@redhat.com>

diff --git a/libmisc/utmp.c b/libmisc/utmp.c
index b35382ef42e767105d07ab721140a20319baaf2e..6e074c27d21957a16ffc9d9b837344ed78a789c8 100644 (file)
--- a/libmisc/utmp.c
+++ b/libmisc/utmp.c
@@ -32,7 +32,7 @@ static bool is_my_tty (const char tty[UT_LINESIZE])
 {
        char         full_tty[STRLEN("/dev/") + UT_LINESIZE + 1];
        /* tmptty shall be bigger than full_tty */
-       static char  tmptty[sizeof (full_tty)+1];
+       static char  tmptty[sizeof(full_tty) + 1];
 
        full_tty[0] = '\0';
        if (tty[0] != '/')
@@ -42,17 +42,15 @@ static bool is_my_tty (const char tty[UT_LINESIZE])
        if ('\0' == tmptty[0]) {
                const char *tname = ttyname (STDIN_FILENO);
                if (NULL != tname)
-                       (void) strlcpy (tmptty, tname, sizeof tmptty);
+                       (void) strlcpy (tmptty, tname, sizeof(tmptty));
        }
 
        if ('\0' == tmptty[0]) {
                (void) puts (_("Unable to determine your tty name."));
                exit (EXIT_FAILURE);
-       } else if (strncmp (full_tty, tmptty, sizeof (tmptty)) != 0) {
-               return false;
-       } else {
-               return true;
        }
+
+       return strcmp (full_tty, tmptty) == 0;
 }
 
 /*