Kenneth Westerback wrote: > On 26 February 2015 at 04:56, Marcus MERIGHI <mcmer-open...@tor.at> wrote: > > hello, > > > > just wanted to let you know that a running iostat automagically adds cd0 > > to it's output when such a device is plugged in: > > > > $ iostat sd0 4 > > tty sd0 cpu > > tin tout KB/t t/s MB/s us ni sy in id > > 2 189 8.90 14 0.12 0 3 3 0 93 > > 0 33 7.60 1 0.01 0 0 1 0 99 > > umass1 at uhub3 port 1 configuration 1 interface 0 "MediaTek Inc MT1887" > > rev 2.00/0.00 addr 3 > > umass1: using ATAPI over Bulk-Only > > scsibus5 at umass1: 2 targets, initiator 0 > > cd0 at scsibus5 targ 1 lun 0: <TSSTcorp, CDDVDW SE-208DB, MF00> ATAPI > > 5/cdrom removable serial.0e8d180676YAF400KW4_ > > tty sd0 cd0 cpu > > tin tout KB/t t/s MB/s KB/t t/s MB/s us ni sy in id > > 0 11 15.09 5 0.08 0.00 0 0.00 0 0 2 0 97 > > 0 46 16.00 0 0.01 0.00 0 0.00 1 0 6 0 93 > > ^C > > $ > > > > This behaviour contradicts iostat(8): "To force iostat to display > > specific drives, their names may be supplied on the command line." > > > > Bye, Marcus > > > > I read the man page as saying that the drives specified on the command > line are always displayed, but if there are other drives they are also > displayed. Up to the limit of 4 drives. i.e. the phrase > > "iostat displays only the first four drives. To force iostat to > display specific drives, ..." > > does not imply that ONLY the drives specified will be displayed. > > Now, whether that is the intended behaviour or just a quirk of the > delightfully flexible english language I can't say.
The way it works, is that *only* the selected drives are displayed at first. But when the set of disks changes, then it changes the selected set. I don't have a test system handy, but I imagine if you were to pick drives sd[6789] on a system with the requisite number, then attach or detach another drive, iostat would wind up displaying sd[1234] instead. Or something. The code, which actually lives in vmstat/dkstat.c, does some rather convoluted tricks. The addition of cd0 to the display is a bug, in my opinion, but it's just the most visible symptom of a rather bigger bug. I don't think now is the time to be fiddling too deeply with this code, but I have some ideas wrt expunging some magic.
