From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jitendra Subject: Re: device mapper mapping across reboot Date: Sat, 10 Mar 2018 16:17:47 +0530 Message-ID: <20180310104747.GA1027@gmail.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Zdenek Kabelac , dm-devel@redhat.com List-Id: dm-devel.ids >lvm2 is exactly solving this problem as it maintains consistent >'metadata' on every device - so upon reboot devices are discovered and >from their metadata dm tables are actived/restored. Got it. >So are you looking for recreation of all the lvm2 infrastructure for >this relatively quite complex task ? Not exactly, but I want to create mapper device created before the root and other fs get mounted so that I can track I/Os in target. >Or you just want to 'create' DM after kernel is booted ? dmsetup create with my target. >Or you even want to pass 'DM' table line on kernel boot option line - >so even your boot device is a 'DM' device ? It is something exactly, I wanna to do. eg. I wrote a basic target as explained here http://techgmm.blogspot.in/p/writing-your-own-device-mapper-target.html Now, to use this target (kernel module), I need to create mapper device as echo 0 basic_target /Path/to/your/device 0 | dmsetup create my_basic_dm_device After creation of device as /dev/mapper/my_basic_dm_device for /dev/sda, if I do I/O from /dev/mapper/my_basic_dm_device, then all I/O goes through basic_target before it hits to /dev/sda. Now, if system is booted and disk is offline then it is very easy to create mapper device. But now let suppose I want to boot on /dev/mapper/my_basic_dm_device instead of /dev/sda1 etc. then I have to create mapper device even before it get switch root. This is same case for other disks as well. So there should be a way so that I can use device mapper framework after reboot. --- Jitendra