This avoids blocking all Ex worker threads in fastfat, thereby making Cc
unable to issue the lazy writes that would unblock those workers.
This is more or less directly taken from fastfat_new.
Cc may decide to process deferred writes any time, so the context might
already be freed by the time we return from CcDeferWrite.
Also mark the IRP as pending, since we're going to return STATUS_PENDING.
- Cache the RootFcb so that its cleanup can be handled separately
during dismounting.
- Force volume dismount at cleanup if the VCB_DISMOUNT_PENDING flag
is set.
- Actually dismount a volume if its VCB has been flagged as not good,
or if we force dismounting.
NOTE: In their *CheckForDismount() function, our 3rd-party FS drivers
as well as MS' fastfat, perform a comparison check of the current VCB's
VPB ReferenceCount with some sort of "dangling"/"residual" open count.
It seems to be related to the fact that the volume root directory as
well as auxiliary data stream(s) are still opened, and only these are
allowed to be opened at that moment. After analysis it appears that for
the ReactOS' fastfat, this number is equal to "3".
- On dismounting, cleanup and destroy the RootFcb, VolumeFcb and the
FATFileObject. Then cleanup the SpareVPB or the IoVPB members, and
finish by removing the dismounted volume from the VolumeListEntry
and cleaning up the notify synchronization object and the resources.
- During dismounting, and on shutdown, flush the volume before
resetting its dirty bit.
- On shutdown, after volume flushing, try to unmount it without forcing.
- Release the VCB resources only when we actually dismount the volume
in VfatCheckForDismount().
- Initialize first the notify list and the synchronization object,
before sending the FSRTL_VOLUME_MOUNT notification.
- If we failed at mounting a volume but its VCB's FATFileObject was
already initialized, first call CcUninitializeCacheMap() on it
before dereferencing it.
- Send FSRTL_VOLUME_LOCK, FSRTL_VOLUME_LOCK_FAILED and
FSRTL_VOLUME_UNLOCK notifications during volume locking (and failure)
and volume unlocking.
- Flush the volume before locking it, and clean its dirty bit if needed.
NOTE: In addition to checking for VCB_CLEAR_DIRTY, we also check for the
presence of the VCB_IS_DIRTY flag before cleaning up the dirty bit: this
allows us to not re-clean the bit if it has been previously cleaned.
This is needed for instance in this scenario:
- The volume is locked (it gets flushed and the dirty bit is possibly cleared);
- The volume then gets formatted with a completely different FS, that
possibly clears up the first sector (e.g. BTRFS ignores 1st sector);
- The volume is then dismounted: if we didn't check whether VCB_IS_DIRTY
was set prior to resetting it, we could attempt clearing it again! But
now that the volume's filesystem has been completely changed, we would
then try to modify the dirty bit on an erroneous position on disk!
That's why it should not be touched in this case during dismounting.
- The volume is unlocked (same comment as above), and later can be
detected as being BTRFS.
Before any write operation that would involve caching, ask
the cache controler whether writing would make it exceed its memory
consumption. If so, queue the write operation for later execution.
In case the write operation can wait, then, the FSD operation will be
halted until the write is allowed.
I could test it successfully by copying huge files from a FAT volume to
another. The write is halted until some portions of the file is written
to the disk.
I could also properly install Qt (SDK) on ReactOS with this and less than 1GB RAM:
- https://www.heisspiter.net/~Pierre/rostests/Qt_OS.png
- https://www.heisspiter.net/~Pierre/rostests/Qt_OS2.png
CORE-12081
CORE-14582
CORE-14313
