Re: [PATCH v1] bcache: partition support: add 16 minors per bcacheN device

On Fri, 14 Oct 2016, Wido den Hollander wrote:

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Op 29 september 2016 om 19:11 schreef Emmanuel Florac [off-list ref]:
Le Thu, 29 Sep 2016 18:52:14 +0200 (CEST)
Wido den Hollander [off-list ref] écrivait:

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I agree, but usually you wouldn't partition an MD-RAID either, would
you? OSDs are still holding (so far) ordinary filesystems locally
mounted on the nodes (except for BlueStore AFAIK).

I have partitioned MD-RAID before, works just fine.

Yes, sure. It just doesn't feel right, my  grey-bearded Unix instinct
tingles :)

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The question still remains, can bcache be patched that it allocates
the right minor in the kernel so that it allows for partitions.

Even looks easy... As Sam Yaple made a patch.

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I'm not a kernel nor bcache developer, just looking for somebody who
would be willing to do this. Happy to assist, support and test!

Well if I have some time I may give it a try next week :)

I was wondering if you were able to take a look at this?

Hi Wido,

See below and please test.  It works for me, but I've not done any more 
than create a partition and verify that it was detected.  Use-case 
opinions aside, some may or may not wish to use partitions atop of bcache. 
(If you do, just make sure they are aligned correctly!).

I'll add your tested-by and request a pull for v4.9 unless someone has 
good reason to implement this differently.

Kent, is there any reason to change this implementation?

--
Eric Wheeler

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 849ad44..6e53afd 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c

@@ -58,6 +58,7 @@
 struct workqueue_struct *bcache_wq;
 
 #define BTREE_MAX_PAGES		(256 * 1024 / PAGE_SIZE)
+#define BCACHE_MINORS		16 /* partition support */
 
 /* Superblock */
 

@@ -783,8 +784,10 @@ static int bcache_device_init(struct bcache_device *d, unsigned block_size,
 	if (minor < 0)
 		return minor;
 
+	minor *= BCACHE_MINORS;
+
 	if (!(d->bio_split = bioset_create(4, offsetof(struct bbio, bio))) ||
-	    !(d->disk = alloc_disk(1))) {
+	    !(d->disk = alloc_disk(BCACHE_MINORS))) {
 		ida_simple_remove(&bcache_minor, minor);
 		return -ENOMEM;
 	}