On Mon, May 23, 2016 at 04:09:26PM -0400, Bob Peterson wrote:

I've been looking at this again. Where are the calls to the fs-specific bits
for fiemap?

In the iomap_ops structure passed to iomap_fiemap.

It looks like iomap_fiemap calls iomap_apply, which calls
iomap_fiemap_actor, but that doesn't call any ops->iomap_get_iomap or similar.
It calls the iomap_begin (which BTW has a comment that says "Execute a iomap
write" which is probably wrong and should be more generic, as for cases like
fiemap) and it calls iomap_end. But it never calls an fs-specific actor
anywhere. Am I missing something? My earlier version passed in the actor
function, as per Dave Chinner's request, but yours doesn't.

The iomap_begin callback is where you do the mapping.  the iomap_end
callback does any required cleanup, which in case of GFS2 probably
would be dropping the cluster lock protecting the mapping.

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