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authorAlan D. Brunelle <alan.brunelle@hp.com>2010-09-16 09:26:22 -0400
committerAlan D. Brunelle <alan.brunelle@hp.com>2010-09-16 09:26:22 -0400
commitce2151ebdca6f2741dbd903aa3845c56adcba8f4 (patch)
tree4c69b8f9136a8d709d535aff93567b876e5e59b7 /doc/blktrace.8
parentfb7f86674a516ddff0d60bfab3bd284a4812075f (diff)
downloadblktrace-ce2151ebdca6f2741dbd903aa3845c56adcba8f4.tar.gz
blktrace-ce2151ebdca6f2741dbd903aa3845c56adcba8f4.tar.bz2
blktrace: disallow -o when using multiple devices
Document that "-o" does not work when specyfing multiple devices to blktrace, also: enforce this by stopping blktrace when one tries do do this. The technical reason why "-o" doesn't work with multiple devices is because we use multiple threads of execution - one per device/CPU pair - and each of them opens a file named "<prefix>.blktrace.<cpu>". With the "-o" all of the "<prefix>" values are the same - so multiple threads open the same file and try to do output. Not good. Without the "-o" we get unique files named: "<device>.blktrace.<cpu>" - as the tuple (<device>,<cpu>) is unique. Signed-off-by: Alan D. Brunelle <Alan.Brunelle@hp.com>
Diffstat (limited to 'doc/blktrace.8')
-rw-r--r--doc/blktrace.83
1 files changed, 3 insertions, 0 deletions
diff --git a/doc/blktrace.8 b/doc/blktrace.8
index ab6a3f3..50b3a62 100644
--- a/doc/blktrace.8
+++ b/doc/blktrace.8
@@ -122,6 +122,9 @@ Specifies number of buffers to use. blktrace defaults to 4 sub buffers.
\-\-output=\fIfile\fR
.RS
Prepend \fIfile\fR to output file name(s)
+
+This only works when supplying a single device, or when piping the output
+via "-o -" with multiple devices.
.RE
\-r \fIrel-path\fR