revert previous now that MAP_ALIGNED has been fixed.

correct previous cast.

cast for lint

branches: 1.27.38;
Deal with __MACHINE_STACK_GROWS_UP machines.

constify the other psize while I'm here.

Thanks to Christos for looking.

branches: 1.26.2;
puffs_cc_yield: fix a cc leak. PR/44679

puffs__cc_destroy: clear PCC_HASCALLER. the caller info is not
necessarily relevant to the next life of the cc. this also fixes
the failure of the assertion in the next line.

branches: 1.24.2;
typo in a comment

clear cached puffs_cc's in puffs_exit()

* make sure we come out of mainloop in the main context. otherwise in
certain cases the server would jump to hyperspace when unmounted
* sprinkle some debug prints

branches: 1.21.6;
Don't add asserts between testing and commit - especially not
if you're going to write "assert(foo = 0)"

Implement lazy contexts for file systems using puffs_mainloop().
Previously each request was executed on its own callcontext and
switched to every time the request was being processed. Now requests
borrow the mainloop context and switch only if/when they yield.
This takes two context switches away from a file system request
bringing down the typical amounts 2->0 (e.g. dtfs) and 4->2 (e.g.
psshfs).

The interfaces for manually executing requests changed a bit:
puffs_dispatch_create() and puffs_dispatch_exec() must now be used.
They are not tested, as nothing in-tree wants them and I doubt
anyone else is really interested in them either.

Also do some misc code cleanup related to execution contexts. The
"work-in-progress checkpoint" committed over a year ago was starting
to look slightly weed-infested.

Fix fakecc case.

Noticed by Pavel Jirout on current-users

Cache a number of execution contexts instead of re-initializing
them every time. Speeds up pure in-memory file systems such as
sysctlfs or dtfs quite a bit. For actual I/O-workhorses the result
is of course less tasty.

Use PROT_NONE page to protect bottom of stack from overrun

* nuke puffs_cc_get{specific,usermount} for good
* move prototypes for puffs_docc and puffs_dopufbuf into the
public header, as they are should be exposed

Part 3/n of extensive changes to message handling:

Get rid of the original puffs_req(3) framework and use puffs_framebuf(3)
instead for file system requests. It has the advantage of being
suitable for transporting a distributed message passing protocol
and therefore us being able to run the file system server on any
host.

Ok, puffs is not quite here yet: libpuffs needs to grow request
routing support and the message contents need to be munged into a
host independent format. Saying which format would be telling,
but it might begin with an X, end in an L and have the 13th character
in the middle. Keep an eye out for the sequels: Parts 3+m/n.

* allocate pcc as a slice from the stack instead of allocating it
separately
* provide puffs_cc_getcc()

This is in preparation for the removal of you-should-guess-what as
an argument to routines here and there and everywhere.

Fix a few bugs and memleaks with the threading code.

Add some very initial support for a threading worker model as an
alternative to the (vastly superior ;) continuation model. This
is very preliminary stuff and not compiled by default (which it
even won't do without some other patches I cannot commit yet).

The raison d'commit of the patch is a snippet which ensures proper
in-order dispatching of all operations, including those which don't
require a response. Previously many of them would be dispatched
simultaneosly, e.g. fsync and reclaim on the same node, which
obviously isn't all that nice for correct operation.

mmap stacks, makes it possible to align them

Add puffs_cc_schedule() which marks a pcc runnable and will pass
execution to it when in the main loop the next time.

Always provide caller information from the kernel based on curlwp.
(but don't deprecate the old puffs_cid interface just yet)

Part 1/n of some pretty extensive changes to how the kernel module
interacts with the userspace file server:

* since the kernel-user communication is not purely request-response
anymore (hasn't been since 2006), try to rename some "request" to
"message". more similar mangling will take place in the future.

* completely rework how messages are allocated. previously most of
them were borrowed from the stack (originally *all* of them),
but now always allocate dynamically. this makes the structure
of the code much cleaner. also makes it possible to fix a
locking order violation. it enables plenty of future enhancements.

* start generalizing the transport interface to be independent of puffs

* move transport interface to read/write instead of ioctl. the
old one had legacy design problems, and besides, ioctl's suck.
implement a very generic version for now; this will be
worked on later hopefully some day reaching "highly optimized".

* implement libpuffs support behind existing library request
interfaces. this will change eventually (I hate those interfaces)

branches: 1.7.4;
Move puffs to a two clause license where it already isn't so. And
as agc pointed out, even files with the third clause were already
effectively two clause because of a slight bug in the language...

Step 3 and currently final step of a more general purpose event loop:
support removal and addition of i/o file descriptors on the fly.

* detect closed file descriptors
* automatically free waiters of a dead file descriptor
* give the file server the possibility to specify a callback which
notifies of a dead file descriptor
* move loop function to be a property of the mainloop instead of
framebuf (doesn't change effective behaviour)
* add the possibility to configure a timespec parameter which
attempts to call the loop function periodically
* move the event loop functions from the puffs_framebuf namespace
to puffs_framev to differential between pure memory management
functions

assert that yield/continue is done only with a real continuation

add puffs_cc_getspecific(pcc), which is shorthand for:
puffs_getspecific(puffs_cc_getusermount(pcc))

#include <ucontext.h>

* get rid of the mount callback; it's no great surprise to the
server that it needs to mount the file system backend if it wants
to call mount
* provide some options for getmntopts(), assume that callers will parse
command line (or fstab) args
* reorganize the puffs_cc interface just a bit, preparing for a bigger
revamp later

checkpoint some experimental work-in-progress, namely:

Add support for having multiple outstanding operations. This is done
by exposing enough interfaces so that it is convenient to have the
main event loop in the implementation itself and by providing a
continuation framework for convinient blocking and rescheduling.

works fine, but will undergo further cleanup & development