Rebase after pdopenpid() tests committed.

Add pddupfd test

Since some time, all renames on the specific mount point are serialized. I added the mp->mnt_renamelock a year ago. So it is really not even a journal but just a storage for two dirents, and theirs locationss in the directory blocks. It can be done synchronously to avoid storing more that one exchange entry.

Re-upload pddupfd() diff after pdopenpid() commit.

In D57658#1331127, @mckusick wrote:

This cannot be implemented in UFS since a requirement of its consistency model is that the on-disk image is always consistent. If the directory entries being swapped are in two different disk blocks, then there is no order of writing that will have a consistent filesystem. The only way to ensure consistency is to have a journal that can correct the unwritten directory name with its updated inode number.

Do we want some test to ensure that pdopenpid() has no effect on the target? I mean, ptrace(PT_ATTACH) might cause spurious wakeups (partially mitigated now).

In D58035#1331000, @markj wrote:

In D58035#1330852, @kib wrote:

atomic_store_int(comm, -1);

What is this from?

Please pass the -U999999 argument to the git diff command you used to generate the uploaded patch, for the next time.

Rename hooks->events and move into vm_object.h

In D58018#1330506, @markj wrote:

In D58018#1330488, @kib wrote:

In D58018#1330469, @markj wrote:

We already have pager methods for page insertion and removal, why aren't they sufficient?

I want the hooks to be set on per-object basis, not globally for all pagers of some type. My use case is having objects backing the IOMMU-managed DMA to be swap objects. This is not too useful for busdma, but I believe is doable and might be not even too hard for bhyve pass-through, assuming I land the iommu/bhyve integration.

At least for now I suggest renaming the hooks to remove the use of "pager".

Done.

atomic_store_int(comm, -1);

Update the comment.

Do not reap on finstall() error.
Man page editing.

i will check this against my branch later. Could you please mail me the git-format patch?

In D58018#1330469, @markj wrote:

We already have pager methods for page insertion and removal, why aren't they sufficient?

In D58018#1330420, @bz wrote:

Would you mind adding a note what this will be good for in the future to the proposed commit message?

In D55957#1330132, @markj wrote:

In D55957#1329686, @kib wrote:

i object against this code structure on principle.

• swp_pager_meta_archXXX should go into the arm64/arm64/somewhere.c. All of them should become arch hooks that do not add any #ifdefs to the sys/vm sources.
• If you absolutely need the extension of the struct swblk, it should be done in a way similar to how struct vm_page gets it MD members.

The space required to store tags is quite large, and we do not want to impose that on all platforms, so this would need to be done with some indirection.

That said, I believe there was some idea circulating about adding hooks to the page lifetime. The motivation for it was e.g. support for demand-paging and page fault events from IOMMUs. Did you considered defining the KPI for hooks on page insertion and removal from the objects, that would allow you to do this stuff without such pollution of the VM code?

Do you mean that the tag metadata should be associated with the VM object, rather than the swap block?

Right now both hooks are called with the object locked, and the 'before_removal' is called with the page xbusied.
I am not sure that this is what needed for the callers: for instance, we might consider xbusying the page for 'after_insert' unconditionally regardless of the vm_page_alloc() mode. Then hooks are allowed to unlock the object if needed.

initialize pgh on object creation.

In D57658#1325551, @kib wrote:

Set WILLBEDIR for fromnd of tvp is VDIR.