From 4177d9f7d3bc8e8bbf8d7bc6fc0df86028e7b066 Mon Sep 17 00:00:00 2001
From: Bryan Drewery <bdrewery@FreeBSD.org>
Date: Tue, 22 Mar 2016 22:41:07 +0000
Subject: [PATCH] Return any log write failure encountered when closing the
 filemon fd.

Discussed with:	sjg, markj
Reviewed by:	sjg
MFC after:	2 weeks
Sponsored by:	EMC / Isilon Storage Division
---
 share/man/man4/filemon.4          |  6 ++++++
 sys/dev/filemon/filemon.c         | 24 ++++++++++++++++++++++--
 sys/dev/filemon/filemon_wrapper.c |  5 ++++-
 3 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/share/man/man4/filemon.4 b/share/man/man4/filemon.4
index 60f622dd13b..8b78d1b0c07 100644
--- a/share/man/man4/filemon.4
+++ b/share/man/man4/filemon.4
@@ -161,6 +161,12 @@ No process having the specified process ID exists.
 The process ID specified is already being traced and was not the current
 process.
 .El
+.Pp
+The
+.Fn close
+system call on the filemon file descriptor may fail with the errors from
+.Xr write 2
+if any error is encountered while writing the log.
 .Sh FILES
 .Bl -tag -width ".Pa /dev/filemon"
 .It Pa /dev/filemon
diff --git a/sys/dev/filemon/filemon.c b/sys/dev/filemon/filemon.c
index 37b9be672c5..564d0f16fb0 100644
--- a/sys/dev/filemon/filemon.c
+++ b/sys/dev/filemon/filemon.c
@@ -92,6 +92,7 @@ struct filemon {
 	char		fname1[MAXPATHLEN]; /* Temporary filename buffer. */
 	char		fname2[MAXPATHLEN]; /* Temporary filename buffer. */
 	char		msgbufr[1024];	/* Output message buffer. */
+	int		error;		/* Log write error, returned on close(2). */
 	u_int		refcnt;		/* Pointer reference count. */
 	u_int		proccnt;	/* Process count. */
 };
@@ -277,7 +278,10 @@ filemon_close_log(struct filemon *filemon)
 	return;
 }
 
-/* The devfs file is being closed.  Untrace all processes. */
+/*
+ * The devfs file is being closed.  Untrace all processes.  It is possible
+ * filemon_close/close(2) was not called.
+ */
 static void
 filemon_dtr(void *data)
 {
@@ -422,12 +426,28 @@ filemon_open(struct cdev *dev, int oflags __unused, int devtype __unused,
 	return (error);
 }
 
+/* Called on close of last devfs file handle, before filemon_dtr(). */
 static int
 filemon_close(struct cdev *dev __unused, int flag __unused, int fmt __unused,
     struct thread *td __unused)
 {
+	struct filemon *filemon;
+	int error;
 
-	return (0);
+	if ((error = devfs_get_cdevpriv((void **) &filemon)) != 0)
+		return (error);
+
+	sx_xlock(&filemon->lock);
+	filemon_close_log(filemon);
+	error = filemon->error;
+	sx_xunlock(&filemon->lock);
+	/*
+	 * Processes are still being traced but won't log anything
+	 * now.  After this call returns filemon_dtr() is called which
+	 * will detach processes.
+	 */
+
+	return (error);
 }
 
 static void
diff --git a/sys/dev/filemon/filemon_wrapper.c b/sys/dev/filemon/filemon_wrapper.c
index 3acf92c9147..3270600efcb 100644
--- a/sys/dev/filemon/filemon_wrapper.c
+++ b/sys/dev/filemon/filemon_wrapper.c
@@ -46,6 +46,7 @@ filemon_output(struct filemon *filemon, char *msg, size_t len)
 {
 	struct uio auio;
 	struct iovec aiov;
+	int error;
 
 	if (filemon->fp == NULL)
 		return;
@@ -63,7 +64,9 @@ filemon_output(struct filemon *filemon, char *msg, size_t len)
 	if (filemon->fp->f_type == DTYPE_VNODE)
 		bwillwrite();
 
-	fo_write(filemon->fp, &auio, curthread->td_ucred, 0, curthread);
+	error = fo_write(filemon->fp, &auio, curthread->td_ucred, 0, curthread);
+	if (error != 0)
+		filemon->error = error;
 }
 
 static int