more strict KPI for vm_pager_get_pages()

[Gleb Smirnoff]

On Mon, May 04, 2015 at 11:24:26AM +0300, Konstantin Belousov wrote:
K> Below is the summary of my part of the internal discussion about the changes.

Quite short. Is it truncated? 

K> Traditionally, Unix allows the filesystems to perform the short reads.
K> Most fundamental change in the patch removes this freedom from the
K> filesystem implementation, and I think that only local filesystems could
K> be compliant with the proposed strictness.
K> 
K> IMO, the response from vm_pager_haspages() is only advisory, since
K> filesystem might not control the external entities which are the source
K> of the required data.

That's why remote filesystems use vop_stdbmap() (or similar), which
always return zeroes for "after" and "before" hints.

-- 
Totus tuus, Glebius.