[patch] blktrace: disable kill option - take 2

[Edward Shishkin <edward@redhat.com>]

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Fixup for 513950.

Problem:
'blktrace -d <device> -k' does not kill a running
backgound trace. Executing 'blktrace -d <device> -k'
for the second time results in "BLKTRACETEARDOWN:
Invalid argument" message and then each run of
blktrace on that machine prints the following output:
BLKTRACESETUP: No such file or directory.

The bug:
The option -k results in clobbering information
about running trace by kernel (blk_trace_remove),
while resources (files open in debugfs by the running
background blktrace) are not released.

Solution:
Update documentation:
Undocument the non-working "kill" option. Advise
to send SIGINT signall via kill(1) to the running
background blktrace for its correct termination.

Signed-off-by: Edward Shishkin <edward@redhat.com>
---
 blktrace.c     |    1 -
 doc/blktrace.8 |   24 ++++--------------------
 2 files changed, 4 insertions(+), 21 deletions(-)

--- blktrace.orig/blktrace.c
+++ blktrace/blktrace.c
@@ -442,7 +442,6 @@ static char usage_str[] = \
 	"\t-r Path to mounted debugfs, defaults to /sys/kernel/debug\n" \
 	"\t-o File(s) to send output to\n" \
 	"\t-D Directory to prepend to output file names\n" \
-	"\t-k Kill a running trace\n" \
 	"\t-w Stop after defined time, in seconds\n" \
 	"\t-a Only trace specified actions. See documentation\n" \
 	"\t-A Give trace mask as a single value. See documentation\n" \
--- blktrace.orig/doc/blktrace.8
+++ blktrace/doc/blktrace.8
@@ -66,19 +66,10 @@ blktrace may also be run concurrently wi
 .TP 2
 \- 
 The default behaviour for blktrace is to run forever until explicitly
-killed by the user (via a control-C, or kill utility invocation).
-There are two ways to modify this:
-
-.TP 5
-  1. 
-You may utilise the blktrace utility itself to kill
-a running trace -- via the \fB\-k\fR option.
-
-.TP 5
-  2.
-You can specify a run-time duration for blktrace via the
-\fB\-w\fR option -- then blktrace will run for the specified number
-of seconds, and then halt.
+killed by the user (via a control-C, or sending SIGINT signal to the
+process via invocation the kill (1) utility). Also you can specify a
+run-time duration for blktrace via the \fB\-w\fR option -- then
+blktrace will run for the specified number of seconds, and then halt.
 
 
 .SH OPTIONS
@@ -119,13 +110,6 @@ Adds \fIdev\fR as a device to trace  
 Adds the devices found in \fIfile\fR as devices to trace
 .RE
 
-\-k 
-.br
-\-\-kill 
-.RS
-Kill on-going trace  
-.RE
-
 \-n \fInum\-sub\fR 
 .br
 \-\-num\-sub=\fInum-sub\fR