InodeVMObjects now track dirty and clean pages. This tracking of
dirty and clean pages is used by the msync and purge syscalls.
dirty page tracking works using the following rules:
* when a new InodeVMObject is made, all pages are marked clean.
* writes to clean InodeVMObject pages will cause a page fault,
the fault handler will mark the page as dirty.
* writes to dirty InodeVMObject pages do not cause page faults.
* if msync is called, only dirty pages are flushed to storage (and
marked clean).
* if purge syscall is called, only clean pages are discarded.
The methods try_release_clean_pages() and release_all_clean_pages() in
InodeVMObject are almost identical. This commit makes them both use the
same code path.
In the VMObject code there are multiple examples of loops over
the VMObject's regions (using for_each_region()) that call remap()
on each region.
To clean up usage of this pattern, this patch adds a method in
VMObject that does this remapping loop. VMObject code that needs
to remap its regions call the new method.
I believe this to be safe, as the main thing that LockRefPtr provides
over RefPtr is safe copying from a shared LockRefPtr instance. I've
inspected the uses of RefPtr<PhysicalPage> and it seems they're all
guarded by external locking. Some of it is less obvious, but this is
an area where we're making continuous headway.
This allows sys$mprotect() to honor the original readable & writable
flags of the open file description as they were at the point we did the
original sys$mmap().
IIUC, this is what Dr. POSIX wants us to do:
https://pubs.opengroup.org/onlinepubs/9699919799/functions/mprotect.html
Also, remove the bogus and racy "W^X" checking we did against mappings
based on their current inode metadata. If we want to do this, we can do
it properly. For now, it was not only racy, but also did blocking I/O
while holding a spinlock.
Until now, our kernel has reimplemented a number of AK classes to
provide automatic internal locking:
- RefPtr
- NonnullRefPtr
- WeakPtr
- Weakable
This patch renames the Kernel classes so that they can coexist with
the original AK classes:
- RefPtr => LockRefPtr
- NonnullRefPtr => NonnullLockRefPtr
- WeakPtr => LockWeakPtr
- Weakable => LockWeakable
The goal here is to eventually get rid of the Lock* classes in favor of
using external locking.
Previously, we could only release *all* clean pages.
This patch makes it possible to release a specific amount of clean
pages. If the attempted number of pages to release is more than the
amount of clean pages, all clean pages will be released.
This commit moves the allocation of the resources required for
InodeVMObject from its constructors to the constructors of its child
classes.
We're making this change to give the child classes the chance to expose
the fallibility of the allocation.
This commit moves the allocation of the resources required for VMObject
from its constructors to the constructors of its child classes.
We're making this change to give the child classes the chance to expose
the fallibility of the allocation.
