On Mon, 29 Aug 2011 20:17:34 +0300 Alexander Lyakas <alex.bolshoy@xxxxxxxxx>
wrote:
> Greetings everybody,
>
> I issue
> mdadm --stop /dev/md0
> and I want to reliably determine that the MD devnode (/dev/md0) is gone.
> So I look for the udev 'remove' event for that devnode.
> However, in some cases even after I see the udev event, I issue
> mdadm --detail /dev/md0
> and I get:
> mdadm: md device /dev/md0 does not appear to be active
>
> According to Detail.c, this means that mdadm can successfully do
> open("/dev/md0") and receive a valid fd.
> But later, when issuing ioctl(fd, GET_ARRAY_INFO) it receives ENODEV
> from the kernel.
>
> Can somebody suggest an explanation for this behavior? Is there a
> reliable way to know when a MD devnode is gone?
run "udevadm settle" after stopping /dev/md0 is most likely to work.
I suspect that udev removes the node *after* you see the 'remove' event.
Sometimes so soon after that you don't see the lag - sometimes a bit later.
NeilBrown
>
> Thanks,
> Alex.
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