Merge branch 'crypto-splice-net-make-af_alg-handle-sendmsg-msg_splice_pages'

David Howells says:

====================
crypto, splice, net: Make AF_ALG handle sendmsg(MSG_SPLICE_PAGES)

Here are patches to make AF_ALG handle the MSG_SPLICE_PAGES internal
sendmsg flag.  MSG_SPLICE_PAGES is an internal hint that tells the protocol
that it should splice the pages supplied if it can.  The sendpage functions
are then turned into wrappers around that.

This set consists of the following parts:

 (1) Move netfs_extract_iter_to_sg() to somewhere more general and rename
     it to drop the "netfs" prefix.  We use this to extract directly from
     an iterator into a scatterlist.

 (2) Make AF_ALG use iov_iter_extract_pages().  This has the additional
     effect of pinning pages obtained from userspace rather than taking
     refs on them.  Pages from kernel-backed iterators would not be pinned,
     but AF_ALG isn't really meant for use by kernel services.

 (3) Change AF_ALG still further to use extract_iter_to_sg().

 (4) Make af_alg_sendmsg() support MSG_SPLICE_PAGES support and make
     af_alg_sendpage() just a wrapper around sendmsg().  This has to take
     refs on the pages pinned for the moment.

 (5) Make hash_sendmsg() support MSG_SPLICE_PAGES by simply ignoring it.
     hash_sendpage() is left untouched to be removed later, after the
     splice core has been changed to call sendmsg().
====================

Link: https://lore.kernel.org/r/20230606130856.1970660-1-dhowells@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>