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-rw-r--r--blktrace.c6
-rw-r--r--doc/blktrace.83
-rw-r--r--doc/blktrace.tex5
3 files changed, 13 insertions, 1 deletions
diff --git a/blktrace.c b/blktrace.c
index b9f9b68..4671a04 100644
--- a/blktrace.c
+++ b/blktrace.c
@@ -2626,6 +2626,12 @@ int main(int argc, char *argv[])
goto out;
}
+ if (ndevs > 1 && output_name && strcmp(output_name, "-") != 0) {
+ fprintf(stderr, "-o not supported with multiple devices\n");
+ ret = 1;
+ goto out;
+ }
+
signal(SIGINT, handle_sigint);
signal(SIGHUP, handle_sigint);
signal(SIGTERM, handle_sigint);
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
diff --git a/doc/blktrace.tex b/doc/blktrace.tex
index 54fe451..4d8278e 100644
--- a/doc/blktrace.tex
+++ b/doc/blktrace.tex
@@ -389,7 +389,10 @@ Short & Long & Description \\ \hline\hline
-d \emph{dev} & --dev=\emph{dev} & Adds \emph{dev} as a device to trace \\ \hline
-k & --kill & Kill on-going trace \\ \hline
-n \emph{num-sub} & --num-sub=\emph{num-sub} & Specifies number of buffers to use \\ \hline
--o \emph{file} & --output=\emph{file} & Prepend \emph{file} to output file name(s) \\ \hline
+-o \emph{file} & --output=\emph{file} & Prepend \emph{file} to output file name(s) \\
+ & & \textbf{This only works when using a single device} \\
+ & & \textbf{or when piping the output via \texttt{-o -}} \\
+ & & \textbf{with multiple devices.} \\ \hline
-r \emph{rel-path} & --relay=\emph{rel-path} & Specifies debugfs mount point \\ \hline
-V & --version & Outputs version \\ \hline
-w \emph{seconds} & --stopwatch=\emph{seconds} & Sets run time to the number of seconds specified \\ \hline