On Thu, Sep 13, 2018 at 04:52:09PM +0100, David Howells wrote: > Add two new iterator types to iov_iter: > > (1) ITER_MAPPING > > This walks through a set of pages attached to an address_space that > are pinned or locked, starting at a given page and offset and walking > for the specified amount of space. A facility to get a callback each > time a page is entirely processed is provided. > > This is useful for copying data from socket buffers to inodes in > network filesystems. Interesting... Questions: * what will hold those pages? IOW, where will you unlock/drop/whatnot those sucker? * "callback" sounds dangerous - it appears to imply that you won't copy to/from the same page twice. Not true for a lot of iov_iter users; what happens if you pass such a beast to them? * why not simply "build and populate ITER_BVEC aliasing a piece of mapping", possibly in "grab" and "grab+lock" variants? Those ITER_MAPPING do seem to be related to ITER_BVEC, at the very least. Note, BTW, that iov_iter_get_pages...() might mutate into something similar - "build and populate ITER_BVEC aliasing a piece of given iov_iter". Or, perhaps, a nicer-on-memory analogue of ITER_BVEC - with <offset, bytes, pointer to pages array> instead of <offset, bytes, page> as elements, with the same "populate from mapping" to get something similar to your functionality and "populate from iov_iter" for iov_iter_get_pages... replacement.
