libnvdimm, btt: update the usage section in Documentation
Section 5 about BTT's in kernel usage was quite obsolete, replace it with a simple 'Usage' section that describes how to set up a BTT namespace using the 'ndctl' utility. Signed-off-by: Vishal Verma <vishal.l.verma@intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
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@ -256,28 +256,18 @@ If any of these error conditions are encountered, the arena is put into a read
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only state using a flag in the info block.
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only state using a flag in the info block.
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5. In-kernel usage
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5. Usage
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==================
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========
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Any block driver that supports byte granularity IO to the storage may register
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The BTT can be set up on any disk (namespace) exposed by the libnvdimm subsystem
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with the BTT. It will have to provide the rw_bytes interface in its
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(pmem, or blk mode). The easiest way to set up such a namespace is using the
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block_device_operations struct:
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'ndctl' utility [1]:
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int (*rw_bytes)(struct gendisk *, void *, size_t, off_t, int rw);
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For example, the ndctl command line to setup a btt with a 4k sector size is:
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It may register with the BTT after it adds its own gendisk, using btt_init:
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ndctl create-namespace -f -e namespace0.0 -m sector -l 4k
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struct btt *btt_init(struct gendisk *disk, unsigned long long rawsize,
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See ndctl create-namespace --help for more options.
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u32 lbasize, u8 uuid[], int maxlane);
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note that maxlane is the maximum amount of concurrency the driver wishes to
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[1]: https://github.com/pmem/ndctl
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allow the BTT to use.
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The BTT 'disk' appears as a stacked block device that grabs the underlying block
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device in the O_EXCL mode.
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When the driver wishes to remove the backing disk, it should similarly call
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btt_fini using the same struct btt* handle that was provided to it by btt_init.
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void btt_fini(struct btt *btt);
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