If we encounter a split page, we add two iovecs to the bio, one for the
fragment of the buffer on each side of the split. In order to do this
safely, we must be sure that we always have room for both fragments.
Its possible for a linear abd to have multiple pages, in which case we
want to add the "left" fragment, then a run of proper 4K pages. then
then "right" fragment. In this way we can keep whole pages together as
much possible.
This change handles both cases by noticing a split page. If we don't
have at least two iovecs remaining in the bio, then we abort outright
(allowing the caller to allocate a new bio and try again). We add the
"left" fragment, and note how big we expect the right fragment to be.
Then we load in as many full pages as are available.
When we reach the last iovec, we close out the bio by taking as uch as
is necessary to restore alignment.
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
(cherry picked from commit 173cafcc3d8b6c94c61844c705d7a410f412a18e)
1bd475d6c6