[MOSTLY SOLVED] Bcache device not created

[statikregimen]

I followed this: https://forums.gentoo.org/viewtopic-t-959542.html and looked at the wiki. I also checked out the Arch wiki and did some google-fu. Nothing explains what to do if the device isn't created (or at least not added to /dev). Or I'm blind/retarded.

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# make-bcache --cache /dev/md127
UUID:                   bfc3163f-e8ec-421e-b777-20f893ea7e1a
Set UUID:               f0159be2-a75b-4bd2-950e-a46a101abbaa
version:                0
nbuckets:               243056
block_size:             1
bucket_size:            1024
nr_in_set:              1
nr_this_dev:            0
first_bucket:           1

# make-bcache --bdev /dev/sda1 
UUID:                   c8b2c169-3dff-4caa-96b7-8ca1057fe1f8
Set UUID:               2616cd85-dde4-4d1f-917b-8e411f70a265
version:                1
block_size:             1
data_offset:            16

# ls /dev/bcache*
ls: cannot access '/dev/bcache*': No such file or directory

# ls /sys/block/bcache*
ls: cannot access '/sys/block/bcache*': No such file or directory

I've used this partition set up before (in Ubuntu) - md127 is 128GB RAID0 array of 2 SSDs for the cache.

[russK]

Is it possible you haven't loaded the bcache module?

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# modprobe bcache

[statikregimen]

That is technically true, because I built it in to the kernel

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--- Multiple devices driver support (RAID and LVM)
<*>   Block device as cache
[ ]     Bcache debugging
[ ]     Debug closures

I don't think that matters, though...In fact, don't you sometimes need to do that if you want to put your root partition on a bcache device (note: that's not what I'm doing in this case - i'll be using it for my /home)?

[bbgermany]

Hi,

What happens, if you run the following:

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echo /dev/md127 > /sys/fs/bcache/register
echo /dev/sda1 > /sys/fs/bcache/register

check the syslog afterwards, there should be something like the following:

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[    3.566663] bcache: register_cache() registered cache device sda1
[    4.169683] bcache: register_bdev() registered backing device md127

greets, bb

[statikregimen]

bbgermany,

That works! Now I get my bcache0 device.

The thing that remains to be seen, is if it will persist through reboots. Getting somewhere though...It just seems odd that it didn't get created automatically like I'm used to, via the make-bcache command.

EDIT: It does not... The Arch wiki says "If the /dev/bcache0 device now exists, type exit and continue booting. You will need to fix your initcpio to ensure devices are registered before mounting the root device. " and I'm not sure what that entails yet. I'm sure I can hack around this but it would be nice to have it set up properly.

EDIT2: I finally found this in the official bcache docs (not that I've spent a ton of time on this):

To make bcache devices known to the kernel, echo them to /sys/fs/bcache/register:

echo /dev/sdb > /sys/fs/bcache/register
echo /dev/sdc > /sys/fs/bcache/register

To register your bcache devices automatically, you could add something like
this to an init script:

echo /dev/sd* > /sys/fs/bcache/register_quiet

The Howto forum post mentions making an init script but I misread it and thought it was for when you want to use the bcache device as your root partition. So I overlooked it. I'm going to go with that solution for now to deal with reboots, but would still love to know if something else is wrong with my system such that /dev/bcache0 wasn't created after running the initial setup commands (make-bcache), like all the tutorials/wikis I've read seem to suggest should have happened. The lack of an init script being generated is probably directly due to Gentoo not being a carebear distro

EDIT3: I think this will be my last edit for now... I made the following init script based on another one in my /etc/init.d:

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#!/sbin/openrc-run

depend() {
        before checkfs fsck
        after modules
}

start() {
        echo /dev/sda1 > /sys/fs/bcache/register
        echo /dev/md127 > /sys/fs/bcache/register
        return 0
}

stop() {
        return 0
}

I saved it to /etc/init.d/bcache and then ran:

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cd /etc/init.d/
chmod +x bcache
rc-update add bcache boot

Many huge thanks tor the replies!! <3