Re: [PATCH 1/3] pmem: Initial version of persistent memory driver

[Ross Zwisler]

On Thu, 2015-03-26 at 09:06 +0100, Christoph Hellwig wrote:
> On Wed, Mar 25, 2015 at 02:21:53PM -0600, Ross Zwisler wrote:
> > What needed to be fixed with the partition support?  I used to have real
> > numbers for first_minor and passed into alloc_disk(), but simplified it based
> > on code found in this commit in the nvme driver:
> > 
> > 469071a37afc NVMe: Dynamically allocate partition numbers
> > 
> > This has worked fine for me - is there some test case in which it breaks?
> 
> Yes, if CONFIG_DEBUG_BLOCK_EXT_DEVT isn't set that code doesn't work at all.

I can't figure out a use case that breaks when using dynamically allocated
minors without CONFIG_DEBUG_BLOCK_EXT_DEVT.  The patch that I've been testing
against is at the bottom of this mail.

Here are the minors that I get when creating a bunch of partitions using the
current code with PMEM_MINORS=16, with CONFIG_DEBUG_BLOCK_EXT_DEVT turned off:

pmem0      249:0    0 63.5G  0 rom  
ââpmem0p1  249:1    0    1G  0 part 
ââpmem0p2  249:2    0    1G  0 part 
ââpmem0p3  249:3    0    1G  0 part 
ââpmem0p4  249:4    0    1G  0 part 
ââpmem0p5  249:5    0    1G  0 part 
ââpmem0p6  249:6    0    1G  0 part 
ââpmem0p7  249:7    0    1G  0 part 
ââpmem0p8  249:8    0    1G  0 part 
ââpmem0p9  249:9    0    1G  0 part 
ââpmem0p10 249:10   0    1G  0 part 
ââpmem0p11 249:11   0    1G  0 part 
ââpmem0p12 249:12   0    1G  0 part 
ââpmem0p13 249:13   0    1G  0 part 
ââpmem0p14 249:14   0    1G  0 part 
ââpmem0p15 249:15   0    1G  0 part 
ââpmem0p16 259:0    0    1G  0 part 
ââpmem0p17 259:1    0    1G  0 part 
ââpmem0p18 259:2    0    1G  0 part 

With dynamic minor allocation, with CONFIG_DEBUG_BLOCK_EXT_DEVT turned off:

pmem0      259:0    0 63.5G  0 rom  
ââpmem0p1  259:1    0    1G  0 part 
ââpmem0p2  259:2    0    1G  0 part 
ââpmem0p3  259:3    0    1G  0 part 
ââpmem0p4  259:4    0    1G  0 part 
ââpmem0p5  259:5    0    1G  0 part 
ââpmem0p6  259:6    0    1G  0 part 
ââpmem0p7  259:7    0    1G  0 part 
ââpmem0p8  259:8    0    1G  0 part 
ââpmem0p9  259:9    0    1G  0 part 
ââpmem0p10 259:10   0    1G  0 part 
ââpmem0p11 259:11   0    1G  0 part 
ââpmem0p12 259:12   0    1G  0 part 
ââpmem0p13 259:13   0    1G  0 part 
ââpmem0p14 259:14   0    1G  0 part 
ââpmem0p15 259:15   0    1G  0 part 
ââpmem0p16 259:16   0    1G  0 part 
ââpmem0p17 259:17   0    1G  0 part 
ââpmem0p18 259:18   0    1G  0 part

And with CONFIG_DEBUG_BLOCK_EXT_DEVT turned on:

pmem0      259:262144  0 63.5G  0 rom  
ââpmem0p1  259:786432  0    1G  0 part 
ââpmem0p2  259:131072  0    1G  0 part 
ââpmem0p3  259:655360  0    1G  0 part 
ââpmem0p4  259:393216  0    1G  0 part 
ââpmem0p5  259:917504  0    1G  0 part 
ââpmem0p6  259:65536   0    1G  0 part 
ââpmem0p7  259:589824  0    1G  0 part 
ââpmem0p8  259:327680  0    1G  0 part 
ââpmem0p9  259:851968  0    1G  0 part 
ââpmem0p10 259:196608  0    1G  0 part 
ââpmem0p11 259:720896  0    1G  0 part 
ââpmem0p12 259:458752  0    1G  0 part 
ââpmem0p13 259:983040  0    1G  0 part 
ââpmem0p14 259:32768   0    1G  0 part 
ââpmem0p15 259:557056  0    1G  0 part 
ââpmem0p16 259:294912  0    1G  0 part 
ââpmem0p17 259:819200  0    1G  0 part 
ââpmem0p18 259:163840  0    1G  0 part

With CONFIG_DEBUG_BLOCK_EXT_DEVT the minors are all mangled due to
blk_mangle_minor(), but I think that all three configs work?

Was there maybe confusion between that config option and the GENHD_FL_EXT_DEVT
gendisk flag, which AFAIK are independent?

Is there a use case that breaks when using dynamic minors without
CONFIG_DEBUG_BLOCK_EXT_DEVT?

Thanks,
- Ross

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