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Refactoring pvmove with generic APIs

Jun'ichi Nomura lvm-devel 1 version New

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Cover letter [PATCH pvmove 0/6] Refactoring pvmove with generic APIs

Hi Heinz,

Thanks for the comment.

Quoted 4 lines · Heinz Mauelshagen

it would be better to make this more generic.

Ie. convert_segments(struct lvm_conversion_handler *handler, ...) rather than having a per target conversion function.

Yes, generic interface is nice.
But as for conversion, I think starting from per-target conversion functions is better.

We may have a generic library interface like this:

int lv_convert(struct logical_volume *lv,
struct segment_type *segtype,
struct conversion_param *conv)

The conversion parameters are very specific to segment types. So callers have to set up the conversion_param based on the segtype.

Parameter are perhaps passed as an array of name-value pairs. I.e.

  struct conversion_param {
     int n_params;
     struct {
       const char *name;
       const char *value;
     } *params;

}

conv = { 4,

           { { "mirrors", "3" }, { "region_size", "64" },
             { "log_count", "0" }, { "type", "segment-by-segment" } }
         }

And the segment type handlers interpret it.
I think it's good for external applications using liblvm2 but too much for LVM2 internal use.

What do you think?

Anyway, IMO, it's easy to add a generic wrapper once we make up underlying conversion functions for each segment types. So I think we should focus first on building up working conversion functions.

This pvmove patchset provides segment-by-segment conversion for mirror.
Next step would be whole-lv conversion for mirror. Then we can add a single wrapper for to-mirror conversion.

Thanks,

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Jun'ichi Nomura, NEC Corporation of America

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