Re: gfs2 IOMAP_ZERO confusion

[Bob Peterson <rpeterso@redhat.com>]

----- Original Message -----
| Hi Bob,
| 
| In "GFS2: Implement iomap for block_map" you seem to have misunderstood
| the intention of the IOMAP_ZERO flag.  It it set if iomap_begin is
| called for a zeroing operation, so that we don't allocate new blocks
| for holes or unwritten extents.  It is not supposed to actually zero
| the blocks.  Can you use some other way to communicate you internal
| zeroing request?
| 
Hi Christoph,

I guess I misappropriated the flag because it seemed like a convenient
way to handle the buffer_zeronew() flag for our block_map function.

The problem is: since GFS2 is not extent-based, we have no good way to
mark groups of blocks as needing to be zeroed in the future, for purposes
like fallocate. I wish there was. There's definitely not enough bits in
our (2-bits-per-block) bitmap for that, although that would be nice.

So we can either add in a new iomap flag and do it when it's convenient,
or else handle the zeroing separately from functions that call iomap,
like in gfs2_block_map, fallocate, and so forth. Or perhaps something
that runs in the background like from a workqueue, etc.

What are your thoughts?

Regards,

Bob Peterson
Red Hat File Systems