Fix poll(2) and select(2) for named pipes to return "ready for read"

when all writers, observed by reader, exited. Use writer generation
counter for fifo, and store the snapshot of the fifo generation in the
f_seqcount field of struct file, that is otherwise unused for fifos.
Set FreeBSD-undocumented POLLINIGNEOF flag only when file f_seqcount is
equal to fifo' fi_wgen, and revert r89376.

Fix POLLINIGNEOF for sockets and pipes, and return POLLHUP for them.
Note that the patch does not fix not returning POLLHUP for fifos.

PR:	kern/94772
Submitted by:	bde (original version)
Reviewed by:	rwatson, jilles
Approved by:	re (kensmith)
MFC after:	6 weeks (might be)

1 files changed, 14 insertions, 20 deletions

diff --git a/sys/fs/fifofs/fifo_vnops.c b/sys/fs/fifofs/fifo_vnops.c
index d328f3b..25436c7 100644
--- a/sys/fs/fifofs/fifo_vnops.c
+++ b/sys/fs/fifofs/fifo_vnops.c
@@ -84,6 +84,7 @@ struct fifoinfo {
 	struct socket	*fi_writesock;
 	long		fi_readers;
 	long		fi_writers;
+	int		fi_wgen;
 };
 
 static vop_print_t	fifo_print;
@@ -232,6 +233,7 @@ fail1:
 				sowwakeup(fip->fi_writesock);
 			}
 		}
+		fp->f_seqcount = fip->fi_wgen - fip->fi_writers;
 	}
 	if (ap->a_mode & FWRITE) {
 		if ((ap->a_mode & O_NONBLOCK) && fip->fi_readers == 0) {
@@ -279,6 +281,9 @@ fail1:
 				fip->fi_writers--;
 				if (fip->fi_writers == 0) {
 					socantrcvmore(fip->fi_readsock);
+					mtx_lock(&fifo_mtx);
+					fip->fi_wgen++;
+					mtx_unlock(&fifo_mtx);
 					fifo_cleanup(vp);
 				}
 				return (error);
@@ -395,8 +400,12 @@ fifo_close(ap)
 	}
 	if (ap->a_fflag & FWRITE) {
 		fip->fi_writers--;
-		if (fip->fi_writers == 0)
+		if (fip->fi_writers == 0) {
 			socantrcvmore(fip->fi_readsock);
+			mtx_lock(&fifo_mtx);
+			fip->fi_wgen++;
+			mtx_unlock(&fifo_mtx);
+		}
 	}
 	fifo_cleanup(vp);
 	return (0);
@@ -634,28 +643,13 @@ fifo_poll_f(struct file *fp, int events, struct ucred *cred, struct thread *td)
 	levents = events &
 	    (POLLIN | POLLINIGNEOF | POLLPRI | POLLRDNORM | POLLRDBAND);
 	if ((fp->f_flag & FREAD) && levents) {
-		/*
-		 * If POLLIN or POLLRDNORM is requested and POLLINIGNEOF is
-		 * not, then convert the first two to the last one.  This
-		 * tells the socket poll function to ignore EOF so that we
-		 * block if there is no writer (and no data).  Callers can
-		 * set POLLINIGNEOF to get non-blocking behavior.
-		 */
-		if (levents & (POLLIN | POLLRDNORM) &&
-		    !(levents & POLLINIGNEOF)) {
-			levents &= ~(POLLIN | POLLRDNORM);
-			levents |= POLLINIGNEOF;
-		}
-
 		filetmp.f_data = fip->fi_readsock;
 		filetmp.f_cred = cred;
+		mtx_lock(&fifo_mtx);
+		if (fp->f_seqcount == fip->fi_wgen)
+			levents |= POLLINIGNEOF;
+		mtx_unlock(&fifo_mtx);
 		revents |= soo_poll(&filetmp, levents, cred, td);
-
-		/* Reverse the above conversion. */
-		if ((revents & POLLINIGNEOF) && !(events & POLLINIGNEOF)) {
-			revents |= (events & (POLLIN | POLLRDNORM));
-			revents &= ~POLLINIGNEOF;
-		}
 	}
 	levents = events & (POLLOUT | POLLWRNORM | POLLWRBAND);
 	if ((fp->f_flag & FWRITE) && levents) {