Re: [Qemu-devel] [PATCH v4 0/4] block: Block driver callbacks fixes

[Markus Armbruster <armbru@redhat.com>]

Manos Pitsidianakis <el13635@mail.ntua.gr> writes:

> This series makes implementing some of the bdrv_* callbacks easier for block
> filters by passing requests to bs->file if bs->drv doesn't implement it instead
> of failing, and adding default bdrv_co_get_block_status() implementations.
>
> This is based against Kevin Wolf's block branch, commit
> da4bd74d2450ab72a7c26bbabb10c6a287dd043e

Haven't seen BlockDriver member is_filter before.  Interesting.  It's
documentation

    /* set to true if the BlockDriver is a block filter */
    bool is_filter;

is seriously lacking.  What does it *mean* to be a block filter?  Which
block layer facilities are affected, and how?

Observation: driver "raw" is filter-like in the sense that all it does
is pass along method arguments and results.  Can't say whether that
makes it a filter in the sense of is_filter, because "the sense of
is_filter" is nebulous to me :)