Christoph Hellwig wrote:
On Fri, Feb 19, 2010 at 01:20:25AM +0100, Douglas Gilbert wrote:
So send a START_STOP_UNIT(stop) through the SG_IO
ioctl on a sd device opened RW and as a bonus get
three INQUIRYs (one standard, two VPD pages) and 5 READ
commands!
If the device is SCSI (as the scsi_debug driver is
simulating) then those READs fail because the drive
is stopped. However if that is an ATA disk behind a
SAT layer, then the disk will be spun up. That defeats
the purpose of the pass-though, especially when it
is being used to spin down the disk.
My guess, reviewing the bug reports flowing into me is
that this nonsense started around lk 2.6.29 .
We should never send INQUIRY or READ commands from the kernel
in response to opening a device. But the combination sounds
like something udev might be doing for it's stable device
indentifier and manual partition scan because I don't trust
the kernel thing. Can you check if these commands come from
udev or one of the realted tools (hal, device-kit-blah, udisks
whatever it is called today)
Adding some sleep()s to sg_start it seems that all nasty
stuff gets sent to the device synchronized with the close()
of the /dev/sd* file descriptor (not the open() ).
The sg_start sequence is:
a) fd = open("/dev/sdb", O_RDWR | O_NOBLOCK)
b) ioctl(fd, SG_IO, <START_STOP_UNIT(stop) command>)
c) close(fd)
a) sends no SCSI commands to the device
b) sends the START_STOP_UNIT(stop) only
c) sends 3 INQUIRYs and 5 READs !?
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