A bcache device provides accelerated access to a backing device in a one
to one relationship. Multiple bcache backing devices can be attached to
and accelerated by the same cache device. Extending the setup from the
previous commit, create an additional backing device and attach it to
the same cache.
# bcache make -B /dev/sdb2
# bcache attach /dev/sdc1 /dev/sdb2
# bcache show
Name Type State Bname AttachToDev
/dev/sdb2 1 (data) clean(running) bcache1 /dev/sdc1
/dev/sdb1 1 (data) clean(running) bcache0 /dev/sdc1
/dev/sdc1 3 (cache) active N/A N/A
List a couple of bcache specific sysfs files which identify registered
(active) bcache devices (components).
# ls -l /sys/block/sd?/sd??/bcache/{dev,set}
lrwxrwxrwx. 1 root root 0 Jan 7 10:08 /sys/block/sdb/sdb1/bcache/dev -> ../../../../../../../../../../virtual/block/bcache0
lrwxrwxrwx. 1 root root 0 Jan 7 11:53 /sys/block/sdb/sdb2/bcache/dev -> ../../../../../../../../../../virtual/block/bcache1
lrwxrwxrwx. 1 root root 0 Jan 7 11:53 /sys/block/sdc/sdc1/bcache/set -> ../../../../../../../../../../../fs/bcache/9945e165-0604-4f29-94bd-b155d01080ad
As was done with previous software block devices [1][2][3][4] show the
bcache (access) device as the mount point of a backing device
(component). Use the /sys/block/DEV[/PTN]/bcache/dev sysfs symlinks to
provide the bcache device names. Bcache cache devices (components)
don't get mount points because they aren't accessible.
[1] commit 8083f11d84
Display LVM2 VGNAME as the PV's mount point (#160787)
[2] commit f6c2f00df7
Populate member mount point with SWRaid array device (#756829)
[3] commit 538c866d09
Display array device as mount point of mdadm started ATARAID members
(#75)
[4] commit 538c866d09
Display array device as mount point of mdadm started ATARAID members
(#75)
Closes#183 - Basic support for bcache
Make (format as) bcache backing device (-B) and cache device (-C) and
implicitly attach the backing device to the cache to enable caching, all
in one.
# bcache make -B /dev/sdb1 -C /dev/sdc1
# bcache show
Name Type State Bname AttachToDev
/dev/sdb1 1 (data) clean(running) bcache0 /dev/sdc1
/dev/sdc1 3 (cache) active N/A N/A
After experimenting with 'bcache unregister', 'bcache register' and
stracing 'bcache show' the bcache kernel module creates the sysfs
directory /sys/block/DEV[/PTN]/bcache and it's contents only when the
bcache device is registered with the kernel (bcache component is
active). Use this to identify whether any bcache device (component)
should be displayed as active or not in GParted.
# ls -ld /sys/block/sd?/sd?1/bcache
drwxr-xr-x. 6 root root 0 Jan 7 10:08 /sys/block/sdb/sdb1/bcache
drwxr-xr-x. 2 root root 0 Jan 7 10:08 /sys/block/sdc/sdc1/bcache
Closes#183 - Basic support for bcache
Mike Fleetwood