Can GEOM be used to intercept the I/o calls to an existing mounted device?

[Tapan Chaudhari]

Hey guys,
      First of all, I was not able to receive your replies to my mail. I
don't know the reason but I am already subscribed to the list. I got to know
about your replies from the digest i received today. I have written a mail
to the mailing list owner describing this problem. Hope this does not happen
again.


Well regarding GEOM as Poul mentioned he has already done this interception
mechanism in GEOM, Poul can you please help me out by giving some directions
as to how to move ahead and implement the interceptions of i/o to a
particular device? I would be really happy to get any help regarding the
interception mechanism.

Thanks,
--Tapan.

On Thu, Jul 10, 2008 at 7:25 PM, Tapan Chaudhari <tapan.list at gmail.com>
wrote:

> Thanks Mark, but unmounting will anyways work. But the problem here will
> be, a new device "/dev/mirror/gm0" and "/dev/mirror/gm0s1" will be created
> after :-
>
> #gmirror label -v -n -b round-robin gm0 /dev/md0
> #gmirror load
> #gmirror configure -a gm0
>
> and "/dev/md0s1" gets deleted.
> Now I will have to mount the new device "/dev/mirror/gm0s1" to get my
> original contents.
> Can't I do it on the fly while the device is already mounted? I just want
> that all the calls going to the device "/dev/md0s1" first come to me and
> then it goes to the original device. In short intercepting the i/o calls. Is
> there some way I can achieve this?
>
> Thanks,
>
>
> On Thu, Jul 10, 2008 at 6:39 PM, Mark Gladman <mark at legios.org> wrote:
>
>> On Thursday 10 July 2008 22:41:25 Tapan Chaudhari wrote:
>> > Hi All,
>> >     I am a newbie to FreeBSD and GEOM. I wanted to intercept the i/o
>> calls
>> > going to a particular mounted device by writing some driver.
>> > I came across  geom and thought it might work. I tried to create a new
>> > device, mount it and then tried using gmirror to mirror the device :-
>> >
>> > #dd if=/dev/zero of=file1 bs=1M count=10
>> > #dd if=/dev/zero of=file2 bs=1M count=10
>> > #mdconfig -f file1
>> > #mdconfig -f file2
>> > #fdisk -B /dev/mirror/md0
>> > #newfs /dev/mirror/md0s1
>> > #mkdir /mnt/mirror0
>> > #mount /dev/mirror/md0s1 /mnt/mirror0/
>> >
>> > #gmirror label -v -n -b round-robin gm0 /dev/md0
>> > gmirror: Can't store metadata on /dev/md0: Operation not permitted.
>> >
>> > It gave me this error "gmirror: Can't store metadata on /dev/md0:
>> Operation
>> > not permitted."
>> >
>> > Am I doing something wrong? Or GEOM does not permit me intercept the i/o
>> > calls? If not geom, is there any other mechanism by which I can achieve
>> it?
>> >
>> >
>> > Thanks,
>> > --Tapan.
>> > _______________________________________________
>> > freebsd-geom at freebsd.org mailing list
>> > http://lists.freebsd.org/mailman/listinfo/freebsd-geom
>> > To unsubscribe, send any mail to "freebsd-geom-unsubscribe at freebsd.org"
>>
>> Hey,
>>
>> You're attempting to set up gmirror on a mounted device.
>> Unmount /dev/mirror/md0s1 then retry the gmirror command and it should
>> work.
>>
>> Cheers!
>> Mark
>>
>
>