Messages in this thread | | | Date | Tue, 23 Nov 2010 00:07:36 -0800 | From | Kent Overstreet <> | Subject | Re: Bcache version 9 |
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On 11/21/2010 05:09 PM, Greg KH wrote: > On Sun, Nov 21, 2010 at 06:09:34AM -0800, Kent Overstreet wrote: >> +++ b/Documentation/bcache.txt > > For new sysfs files, please create Documentation/ABI files. > >> +All configuration is done via sysfs. To use sde to cache md1, assuming the >> +SSD's erase block size is 128k: >> + >> + make-bcache -b128k /dev/sde >> + echo "/dev/sde"> /sys/kernel/bcache/register_cache >> + echo "<UUID> /dev/md1"> /sys/kernel/bcache/register_dev > > /sys/kernel/bcache/? Really?
That was a completely arbitrary choice dating from when I first started hacking on it. No point in moving it when it might be moved again :p
> Come on, shouldn't this be somewhere else? You only have 1 file here, > right?
Two files (really three, but the third is for gimpy latency tracing and will die eventually). register_dev is there so on bootup you don't have to wait for the cache to be discovered - when you add a cache device if there's a backing device waiting for a cache, and the cache has seen that UUID before it'll do what you want.
> Shouldn't it be a configfs file instead as that is what you are doing?
That was one of the possibilities I had in mind. My main issue with that though is I don't see any way to just have a bare config_item - per the documentation, the user must do a mkdir() first, which just doesn't make any sense for bcache. There's no point in having a persistent object besides the one associated with the block device. Maybe there would be in the future, with multiple cache devices, but I still think it's a lousy interface for that problem - what bcache wants is something more like a syscall; you wouldn't use configfs to replace mount(), for example.
There do exist global interfaces in sysfs, not attached to any device - besides /sys/kernel, there's /sys/fs which doesn't have any rhyme or reason to it I can discern. ecryptfs has /sys/ext4/ecryptfs/version, ext4 has per device stuff that you can't find from the device's dir (you woludn't know /sys/fs/ext4/md0 exists from looking at /sys/block/md0). There's also /sys/fs/cgroup, which is another unique thing as far as I can tell...
Then there's /sys/module which has a bunch of ad hoc stuff, but as far as I can tell that's all still module parameters and register_cache and register_dev certainly aren't module parameters.
So anyways, I absolutely agree that there are better solutions than /sys/kernel/bcache but I want to replace it with something correct, not something that sucks less. Ideas/flames are of course more than welcome :)
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