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 <size_of_device> 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 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
