This patch adds most of the plumbing for working file deletion in Ext2FS.
Directory entries are removed and inode link counts updated.
We don't yet update the inode or block bitmaps, I will do that separately.
This was a bit silly. We were always creating Ext2FSInode objects when
Ext2FSInode::get_inode() was called. They'd then sit and fatten up the
inode cache forever, despite not representing allocated inodes.
This patch consults the inode bitmap and if get_inode() is called with
an unallocated inode index, we simply cache a nullptr to represent the
fact that this index is unused.
This could be a lot better optimized, it will currently hit the disk for
every new inode index encountered.
The inode cache was keeping these alive forever. Added a cute little magic
trick to Retainable that calls T::one_retain_left() when the retain count
is decremented to 1.
It walks all the live Inode objects and flushes pending metadata changes
wherever needed.
This could be optimized by keeping a separate list of dirty Inodes,
but let's not get ahead of ourselves.
Use a little template magic to have Retainable::release() call out to
T::will_be_destroyed() if such a function exists before actually calling
the destructor. This gives us full access to virtual functions in the
pre-destruction code.
This synchronous approach to inodes is silly, obviously. I need to rework
it so that the in-memory CoreInode object is the canonical inode, and then
we just need a sync() that flushes pending changes to disk.
...by adding a new class called Ext2Inode that inherits CoreInode.
The idea is that a vnode will wrap a CoreInode rather than InodeIdentifier.
Each CoreInode subclass can keep whatever caches they like.
Right now, Ext2Inode caches the list of block indices since it can be very
expensive to retrieve.
Pass the file name in a stack-allocated buffer instead of using an AK::String
when iterating directories. This dramatically reduces the amount of cycles
spent traversing the filesystem.
This is dirty but pretty cool! If we have a pending, unmasked signal for
a process that's blocked inside the kernel, we set up alternate stacks
for that process and unblock it to execute the signal handler.
A slightly different return trampoline is used here: since we need to
get back into the kernel, a dedicated syscall is used (sys$sigreturn.)
This restores the TSS contents of the process to the state it was in
while we were originally blocking in the kernel.
NOTE: There's currently only one "kernel resume TSS" so signal nesting
definitely won't work.
The SpinLock was all backwards and didn't actually work. Fixing it exposed
how wrong most of the locking here is.
I need to come up with a better granularity here.
This is pretty inefficient for ext2fs. We walk the entire block group
containing the inode, searching through every directory for an entry
referencing this inode.
It might be a good idea to cache this information somehow. I'm not sure
how often we'll be searching for it.
Obviously there are multiple caching layers missing in the file system.
