Date: Tue, 26 Jan 2016 07:57:44 +0000 (UTC) From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r294778 - in head: lib/libc/sys sys/kern Message-ID: <201601260757.u0Q7viGW029949@repo.freebsd.org>
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Author: kib Date: Tue Jan 26 07:57:44 2016 New Revision: 294778 URL: https://svnweb.freebsd.org/changeset/base/294778 Log: Restore flushing of output for revoke(2) again. Document revoke()'s intended behaviour in its man page. Simplify tty_drain() to match. Don't call ttydevsw methods in tty_flush() if the device is gone since we now sometimes call it then. The flushing was supposed to be implemented by passing the FNONBLOCK flag to VOP_CLOSE() for revoke(). The tty driver is one of the few that can block in close and was one of the fewer that knew about this. This almost worked in FreeBSD-1 and similarly in Net/2. These versions only almost worked because there was and is considerable confusion between IO_NDELAY and FNONBLOCK (aka O_NONBLOCK). IO_NDELAY is only valid for VOP_READ() and VOP_WRITE(). For other VOPs it has the same value as O_SHLOCK. But since vfs_subr.c and tty.c consistently used the wrong flag and the O_SHLOCK flag is rarely set, this mostly worked. It also gave the feature than applications could get the non-blocking close by abusing O_SHLOCK. This was first broken then fixed in 1995. I changed only the tty driver to use FNONBLOCK, as a hack to get non-blocking via the normal flag FNONBLOCK for last closes. I didn't know about revoke()'s use of IO_NDELAY or change it to be consistent, so revoke() was broken. Then I changed revoke() to match. This was next broken in 1997 then fixed in 1998. Importing Lite2 made the flags inconsistent again by undoing the fix only in vfs_subr.c. This was next broken in 2008 by replacing everything in tty.c and not checking any flags in last close. Other bugs in draining limited the resulting unbounded waits to drain in some cases. It is now possible to fix this better using the new FREVOKE flag. Just restore flushing for revoke() for now. Don't restore or undo any hacks for ordinary last closes yet. But remove dead code in the 1-second relative timeout (r272789). This did extra work to extend the buggy draining for revoke() for as long as possible. The 1-second timeout made this not very long by usually flushing after 1 second. Submitted by: bde MFC after: 2 weeks Modified: head/lib/libc/sys/revoke.2 head/sys/kern/tty.c Modified: head/lib/libc/sys/revoke.2 ============================================================================== --- head/lib/libc/sys/revoke.2 Tue Jan 26 07:49:11 2016 (r294777) +++ head/lib/libc/sys/revoke.2 Tue Jan 26 07:57:44 2016 (r294778) @@ -31,7 +31,7 @@ .\" @(#)revoke.2 8.1 (Berkeley) 6/4/93 .\" $FreeBSD$ .\" -.Dd June 4, 1993 +.Dd Jan 25, 2016 .Dt REVOKE 2 .Os .Sh NAME @@ -59,7 +59,8 @@ and a system call will succeed. If the file is a special file for a device which is open, the device close function -is called as if all open references to the file had been closed. +is called as if all open references to the file had been closed +using a special close method which does not block. .Pp Access to a file may be revoked only by its owner or the super user. The @@ -104,3 +105,6 @@ The .Fn revoke system call first appeared in .Bx 4.3 Reno . +.Sh BUGS +The non-blocking close method is only correctly implemented for +terminal devices. Modified: head/sys/kern/tty.c ============================================================================== --- head/sys/kern/tty.c Tue Jan 26 07:49:11 2016 (r294777) +++ head/sys/kern/tty.c Tue Jan 26 07:57:44 2016 (r294778) @@ -126,7 +126,7 @@ static int tty_drain(struct tty *tp, int leaving) { size_t bytesused; - int error, revokecnt; + int error; if (ttyhook_hashook(tp, getc_inject)) /* buffer is inaccessible */ @@ -141,18 +141,10 @@ tty_drain(struct tty *tp, int leaving) /* Wait for data to be drained. */ if (leaving) { - revokecnt = tp->t_revokecnt; error = tty_timedwait(tp, &tp->t_outwait, hz); - switch (error) { - case ERESTART: - if (revokecnt != tp->t_revokecnt) - error = 0; - break; - case EWOULDBLOCK: - if (ttyoutq_bytesused(&tp->t_outq) < bytesused) - error = 0; - break; - } + if (error == EWOULDBLOCK && + ttyoutq_bytesused(&tp->t_outq) < bytesused) + error = 0; } else error = tty_wait(tp, &tp->t_outwait); @@ -356,6 +348,10 @@ ttydev_close(struct cdev *dev, int fflag return (0); } + /* If revoking, flush output now to avoid draining it later. */ + if (fflag & FREVOKE) + tty_flush(tp, FWRITE); + /* * This can only be called once. The callin and the callout * devices cannot be opened at the same time. @@ -1460,13 +1456,16 @@ tty_flush(struct tty *tp, int flags) tp->t_flags &= ~TF_HIWAT_OUT; ttyoutq_flush(&tp->t_outq); tty_wakeup(tp, FWRITE); - ttydevsw_pktnotify(tp, TIOCPKT_FLUSHWRITE); + if (!tty_gone(tp)) + ttydevsw_pktnotify(tp, TIOCPKT_FLUSHWRITE); } if (flags & FREAD) { tty_hiwat_in_unblock(tp); ttyinq_flush(&tp->t_inq); - ttydevsw_inwakeup(tp); - ttydevsw_pktnotify(tp, TIOCPKT_FLUSHREAD); + if (!tty_gone(tp)) { + ttydevsw_inwakeup(tp); + ttydevsw_pktnotify(tp, TIOCPKT_FLUSHREAD); + } } }
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