On 2020/08/28 4:14, Sergei Shtepa wrote: > Hello everyone! Requesting for your comments and suggestions. > > We propose new kernel API that should be beneficial for out-of-tree > kernel modules of multiple backup vendors: block layer filter API. > > Functionality: > * Provide callback to intercept bio requests, the main purpose is to > allow block level snapshots for the devices that do not support it, > for example, non-LVM block devices and implementation of changed block > tracking for faster incremental backups without system reconfiguration > or reboot, but there could be other use cases that we have not thought of. > * Allow multiple filters to work at the same time. The order in which the > request is intercepted is determined by their altitude. > * When new block devices appear, send a synchronous request to the > registered filter to add it for filtering. > * If a block device is permanently deleted or disappears, send a > synchronous request to remove the device from filtering. > > Why dm-snap and dm-era is not the solution: > Device mapper must be set up in advance, usually backup vendors have very > little ability to change or convince users to modify the existing setup > at the time of software installation. > One of the most common setups is still a block device without LVM and > formatted with ext4. > Convincing users to redeploy or reconfigure machine, just to make block > level snapshots/backup software work, is a challenging task. And convincing said users to change their kernel is not challenging ? In my experience, that is even harder than trying to get them to change their configuration. > As of now, commit c62b37d96b6e removed make_request_fn from > struct request_queue and our out-of-tree module [1] can no longer > hook/replace it to intercept bio requests. And fops in struct gendisk > is declared as const and cannot be hooked as well. > > We would appreciate your feedback! Upstream your out-of-tree module ? > [1] https://github.com/veeam/veeamsnap > > Sergei Shtepa (1): > block io layer filters api > > block/Kconfig | 11 ++ > block/Makefile | 1 + > block/blk-core.c | 11 +- > block/blk-filter-internal.h | 34 +++++ > block/blk-filter.c | 288 ++++++++++++++++++++++++++++++++++++ > block/genhd.c | 24 +++ > include/linux/blk-filter.h | 41 +++++ > include/linux/genhd.h | 2 + > 8 files changed, 410 insertions(+), 2 deletions(-) > create mode 100644 block/blk-filter-internal.h > create mode 100644 block/blk-filter.c > create mode 100644 include/linux/blk-filter.h > -- Damien Le Moal Western Digital Research
