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+.TH IOSTATS 4
+.SH NAME
+iostats \- file system to measure I/O
+.SH SYNOPSIS
+.B iostats
+[
+.B -d
+]
+[
+.B -f
+.I dbfile
+]
+.I cmd
+[
+.I args...
+]
+.SH DESCRIPTION
+.I Iostats
+is a file server that interposes itself between a program and a copy of the current name space,
+which allows it to gather statistics of file system
+use at the level of the file system protocol of
+.IR intro (5).
+When the program exits,
+a report is printed on standard error.
+.PP
+The report consists of three sections.
+The first section reports the amount
+of user data in
+.B read
+and
+.B write
+messages sent by the program and the average rate at
+which the data was transferred.
+The
+.B protocol
+line reports the amount
+of data sent as message headers, that is,
+protocol overhead.
+The
+.B rpc
+line reports the
+total number of file system transactions.
+.PP
+The second section gives
+the number of messages, the fastest, slowest, and average turn around
+time and the amount of data involved with each 9P
+message type.
+The final section gives an I/O summary for each file used
+by the program in terms of opens, reads and writes.
+.PP
+The
+.B -d
+option causes
+.I iostats
+to write a debugging log to
+.I dbfile
+(default:
+.BR iostats.out )
+that records all protocol messages.
+.SH EXAMPLE
+Display summary of file I/O incurred by
+.IR ls (1):
+.IP
+.EX
+iostats ls
+.EE
+.PP
+Start a new shell, displaying all 9P traffic caused by the shell or its children:
+.IP
+.EX
+iostats -df /fd/1 sh
+.EE
+.SH SOURCE
+.B /appl/cmd/iostats.b
+.SH BUGS
+Poor clock resolution means that large amounts of I/O must be done to
+get accurate rate figures.
+.PP
+Can be fooled by programs that do fresh mounts outside its purview.
+.PP
+Cannot monitor standard input or output.