misc/70798: Compatibility: Sun/Solaris has an fcntl() F_DUP2FD. FreeBSD could support it too.

[Jukka Ukkonen]

>Number:         70798
>Category:       misc
>Synopsis:       Compatibility: Sun/Solaris has an fcntl() F_DUP2FD. FreeBSD could support it too.
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          change-request
>Submitter-Id:   current-users
>Arrival-Date:   Sat Aug 21 19:20:23 GMT 2004
>Closed-Date:
>Last-Modified:
>Originator:     Jukka Ukkonen
>Release:        FreeBSD-4.10-STABLE
>Organization:
Mawit Ltd.
>Environment:
FreeBSD mjolnir 4.10-STABLE FreeBSD 4.10-STABLE #0: Sat Aug 14 11:58:59 EET DST 2004     jau at mjolnir:/home/src/sys/compile/Mjolnir  i386
>Description:
      This is taken from SunOS/Solaris fcntl() manual page...

F_DUP2FD
	Similar to  F_DUPFD, but always returns arg. F_DUP2FD closes
	arg if  it is open and not equal to fildes. F_DUP2FD is
	equivalent to dup2(fildes, arg).

It seems to be very easy to implement this functionality in FreeBSD.

1st step:
	Add a definition for F_DUP2FD in fcntl.h ...

#define F_DUP2FD	10		/* Parallel to dup2() like F_DUPFD is for dup(). */
	
2nd step:
	Add this change to kern_descrip.c ...

--- ../kern_descrip.c.old	Sat May 17 12:10:06 2003
+++ ../kern_descrip.c	Sat May 17 12:10:13 2003
@@ -249,24 +249,35 @@
 	switch (cmd) {
 	case F_DUPFD:
 		FILEDESC_UNLOCK(fdp);
 		newmin = arg;
 		if (newmin >= p->p_rlimit[RLIMIT_NOFILE].rlim_cur ||
 		    newmin >= maxfilesperproc) {
 			error = EINVAL;
 			break;
 		}
 		error = do_dup(td, DUP_VARIABLE, fd, newmin, td->td_retval);
 		break;
 
+	case F_DUP2FD:
+		FILEDESC_UNLOCK(fdp);
+		newmin = arg;
+		if (newmin >= p->p_rlimit[RLIMIT_NOFILE].rlim_cur ||
+		    newmin >= maxfilesperproc) {
+			error = EINVAL;
+			break;
+		}
+		error = do_dup(td, DUP_FIXED, fd, newmin, td->td_retval);
+		break;
+
 	case F_GETFD:
 		td->td_retval[0] = (*pop & UF_EXCLOSE) ? FD_CLOEXEC : 0;
 		FILEDESC_UNLOCK(fdp);
 		break;
 
 	case F_SETFD:
 		*pop = (*pop &~ UF_EXCLOSE) |
 		    (arg & FD_CLOEXEC ? UF_EXCLOSE : 0);
 		FILEDESC_UNLOCK(fdp);
 		break;
 
 	case F_GETFL:

>How-To-Repeat:
      Not an actual problem per se unless a lacking portability feature
is counted as one.

>Fix:
      See "Full Description" above.


>Release-Note:
>Audit-Trail:
>Unformatted: