The 02/01/2021 18:45, Bart Van Assche wrote: > On 1/28/21 9:12 AM, Sergei Shtepa wrote: > > I`m ready to suggest the blk_interposer again. > > blk_interposer allows to intercept bio requests, remap bio to > > another devices or add new bios. > > > > This version has support from device mapper. > > > > For the dm-linear device creation command, the `noexcl` parameter > > has been added, which allows to open block devices without > > FMODE_EXCL mode. It allows to create dm-linear device on a block > > device with an already mounted file system. > > The new ioctl DM_DEV_REMAP allows to enable and disable bio > > interception. > > > > Thus, it is possible to add the dm-device to the block layer stack > > without reconfiguring and rebooting. > > What functionality does this driver provide that is not yet available in > a RAID level 1 (mirroring) driver + a custom dm driver? My understanding > is that there are already two RAID level 1 drivers in the kernel tree > and that both driver support sending bio's to two different block devices. > > Thanks, > > Bart. Hi Bart. The proposed patch is not realy aimed at RAID1. Creating a new dm device in the non-FMODE_EXCL mode and then remaping bio requests from the regular block device to the new DM device using the blk_interposer will allow to use device mapper for regular devices. For dm-linear, there is not much benefit from using blk_interposer. This is a good and illustrative example. Later, using blk-interposer, it will be possible to connect the dm-cache "on the fly" without having to reboot and/or reconfigure. My intention is to let users use dm-snap to create snapshots of any device. blk-interposer will allow to add new features to Device Mapper. As per Daniel's advice I want to add a documentation, I'm working on it now. The documentation will also contain a description of new features that blk_interposer will add to Device Mapper Thanks. -- Sergei Shtepa Veeam Software developer.
