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
This is a PoC of what it's possible to realize thanks to an
already existing hack in ntoskrnl :-).
With this extension, on the kdb:> prompt, you're able to type
in commands that will be handled by the FastFAT driver and not
by the kernel, allowing internal debug, not possible otherwise.
So far, three commands exist:
- ?fat.vols: lists all the mounted volumes by FastFAT
- ?fat.files: lists all the files on a specific volume (with their attributes)
- ?fat.setdbgfile: allows watching on specifics files lifetime
This is obviously only the begin and could be greatly improved.
For instance, this is what allowed to debug CORE-14557
Once a directory is crossed (opened or a child is opened), associated
FCB structure is created in FastFAT, but also a stream FO for caching.
Up to now, due to an extra reference taken by the stream file object,
even when the directory was no longer used, the directory was kept in
memory: the FCB was never deleted, the file object was never dereferenced,
and the cache never released.
The immediate effect of this bug is that our FAT driver was leaking every
directory that was used affecting the whole OS situation. In case of
directories intensive operation (like extraction the ReactOS source code
in ReactOS ;-)), we were just killin the whole OS RAM without any way to
release it and recover.
The other side effects: IOs were faster as half of the FS was always
permanant in RAM.
This commit fixes the issue by forcing the FSD to release the FO,
and the cache when a directory is no longer used, leading to its
destruction in RAM.
Downside: on IO intensive operation, expect slowdowns, obviously,
there's less caching now. But more efficient!
CORE-14557
leaves volumes in half-(dis)mounted state and thus they get remounted while not
completely dismounted.
This can lead to major breakage and data corruption.
This requires deeper fixes (let's just drop that driver!).
CORE-14124
CORE-14126
CORE-14133
It fixes assertion failure in vfatDestroyFCB() where we would have release parent before child.
This is still not perfect, but less bug prone...
With this commits (and ENABLE_SWAPOUT defined), ReactOS seems to unmount FAT volumes quite nice! :-)
(Tried with fsutil volume dismount X:)
This is likely due to a copy paste error where long name was copied twice and short never.
Fun fact: this was not affecting FATX volumes
Fun fact2: this was defeating a buffer overflow check and thus was allowing buffer overflow!
CORE-14088
This commit fixes weird behavior in our FastFAT implementation. It was mixing two classes:
FileNameInformation and FileNamesInformation. It was handling FileNameInformation like
FileNamesInformation and was filling buffer with FILE_NAMES_INFORMATION structure instead
of FILE_NAME_INFORMATION structure (how many things did that break?!).
Also, it wasn't implementing the FileNamesInformation class at all. This is required by
ntdll_winetest:directory which doesn't expect it to fail and thus, attempts to read
never filled in memory.
This commit fixes the winetest crash, and may fix other weird FS behavior.
CORE-13367
