For a long time, our shutdown procedure has basically been:
- Acquire big process lock.
- Switch framebuffer to Kernel debug console.
- Sync and lock all file systems so that disk caches are flushed and
files are in a good state.
- Use firmware and architecture-specific functionality to perform
hardware shutdown.
This naive and simple shutdown procedure has multiple issues:
- No processes are terminated properly, meaning they cannot perform more
complex cleanup work. If they were in the middle of I/O, for instance,
only the data that already reached the Kernel is written to disk, and
data corruption due to unfinished writes can therefore still occur.
- No file systems are unmounted, meaning that any important unmount work
will never happen. This is important for e.g. Ext2, which has
facilites for detecting improper unmounts (see superblock's s_state
variable) and therefore requires a proper unmount to be performed.
This was also the starting point for this PR, since I wanted to
introduce basic Ext2 file system checking and unmounting.
- No hardware is properly shut down beyond what the system firmware does
on its own.
- Shutdown is performed within the write() call that asked the Kernel to
change its power state. If the shutdown procedure takes longer (i.e.
when it's done properly), this blocks the process causing the shutdown
and prevents any potentially-useful interactions between Kernel and
userland during shutdown.
In essence, current shutdown is a glorified system crash with minimal
file system cleanliness guarantees.
Therefore, this commit is the first step in improving our shutdown
procedure. The new shutdown flow is now as follows:
- From the write() call to the power state SysFS node, a new task is
started, the Power State Switch Task. Its only purpose is to change
the operating system's power state. This task takes over shutdown and
reboot duties, although reboot is not modified in this commit.
- The Power State Switch Task assumes that userland has performed all
shutdown duties it can perform on its own. In particular, it assumes
that all kinds of clean process shutdown have been done, and remaining
processes can be hard-killed without consequence. This is an important
separation of concerns: While this commit does not modify userland, in
the future SystemServer will be responsible for performing proper
shutdown of user processes, including timeouts for stubborn processes
etc.
- As mentioned above, the task hard-kills remaining user processes.
- The task hard-kills all Kernel processes except itself and the
Finalizer Task. Since Kernel processes can delay their own shutdown
indefinitely if they want to, they have plenty opportunity to perform
proper shutdown if necessary. This may become a problem with
non-cooperative Kernel tasks, but as seen two commits earlier, for now
all tasks will cooperate within a few seconds.
- The task waits for the Finalizer Task to clean up all processes.
- The task hard-kills and finalizes the Finalizer Task itself, meaning
that it now is the only remaining process in the system.
- The task syncs and locks all file systems, and then unmounts them. Due
to an unknown refcount bug we currently cannot unmount the root file
system; therefore the task is able to abort the clean unmount if
necessary.
- The task performs platform-dependent hardware shutdown as before.
This commit has multiple remaining issues (or exposed existing ones)
which will need to be addressed in the future but are out of scope for
now:
- Unmounting the root filesystem is impossible due to remaining
references to the inodes /home and /home/anon. I investigated this
very heavily and could not find whoever is holding the last two
references.
- Userland cannot perform proper cleanup, since the Kernel's power state
variable is accessed directly by tools instead of a proper userland
shutdown procedure directed by SystemServer.
The recently introduced Firmware/PowerState procedures are removed
again, since all of the architecture-independent code can live in the
power state switch task. The architecture-specific code is kept,
however.
Since we never check a kernel process's state like a userland process,
it's possible for a kernel process to ignore the fact that someone is
trying to kill it, and continue running. This is not desireable if we
want to properly shutdown all processes, including Kernel ones.
This is correct since unmount doesn't treat bind mounts specially. If we
don't do this, unmounting bind mounts will call
prepare_for_last_unmount() on the guest FS much too early, which will
most likely fail due to a busy file system.
This is a preparation before we can create a usable mechanism to use
filesystem-specific mount flags.
To keep some compatibility with userland code, LibC and LibCore mount
functions are kept being usable, but now instead of doing an "atomic"
syscall, they do multiple syscalls to perform the complete procedure of
mounting a filesystem.
The FileBackedFileSystem IntrusiveList in the VFS code is now changed to
be protected by a Mutex, because when we mount a new filesystem, we need
to check if a filesystem is already created for a given source_fd so we
do a scan for that OpenFileDescription in that list. If we fail to find
an already-created filesystem we create a new one and register it in the
list if we successfully mounted it. We use a Mutex because we might need
to initiate disk access during the filesystem creation, which will take
other mutexes in other parts of the kernel, therefore making it not
possible to take a spinlock while doing this.
Instead of using ifdefs to use the correct platform-specific methods, we
can just use the same pattern we use for the microseconds_delay function
which has specific implementations for each Arch CPU subdirectory.
When linking a kernel image, the actual correct and platform-specific
power-state changing methods will be called in Firmware/PowerState.cpp
file.
All code that is related to PC BIOS should not be in the Kernel/Firmware
directory as this directory is for abstracted and platform-agnostic code
like ACPI (and device tree parsing in the future).
This fixes a problem with the aarch64 architecure, as these machines
don't have any PC-BIOS in them so actually trying to access these memory
locations (EBDA, BIOS ROM) does not make any sense, as they're specific
to x86 machines only.
Previously, reads would only be successful for offset 0. For this
reason, the maximum size that could be correctly read from the PCI
expansion ROM SysFS node was limited to the block size, and
subsequent blocks would fail. This commit fixes the computation of
the number of bytes to read.
Like the HID, Audio and Storage subsystem, the Graphics subsystem (which
handles GPUs technically) exposes unix device files (typically in /dev).
To ensure consistency across the repository, move all related files to a
new directory under Kernel/Devices called "GPU".
Also remove the redundant "GPU" word from the VirtIO driver directory,
and the word "Graphics" from GraphicsManagement.{h,cpp} filenames.
This has KString, KBuffer, DoubleBuffer, KBufferBuilder, IOWindow,
UserOrKernelBuffer and ScopedCritical classes being moved to the
Kernel/Library subdirectory.
Also, move the panic and assertions handling code to that directory.
When deleting a directory, the rmdir syscall should fail if the path was
unveiled without the 'c' permission. This matches the same behavior that
OpenBSD enforces when doing this kind of operation.
When deleting a file, the unlink syscall should fail if the path was
unveiled without the 'w' permission, to ensure that userspace is aware
of the possibility of removing a file only when the path was unveiled as
writable.
When using the userdel utility, we now unveil that directory path with
the unveil 'c' permission so removal of an account home directory is
done properly.
The Storage subsystem, like the Audio and HID subsystems, exposes Unix
device files (for example, in the /dev directory). To ensure consistency
across the repository, we should make the Storage subsystem to reside in
the Kernel/Devices directory like the two other mentioned subsystems.
The contents of the directory inode could change if we are not taking so
we must take the m_inode_lock to prevent corruption when reading the
directory contents.
This is not needed, because when we are doing this traversing, functions
that are called from this function are using proper and more "atomic"
locking.
"Wherever applicable" = most places, actually :^), especially for
networking and filesystem timestamps.
This includes changes to unzip, which uses DOSPackedTime, since that is
changed for the FAT file systems.
That's what this class really is; in fact that's what the first line of
the comment says it is.
This commit does not rename the main files, since those will contain
other time-related classes in a little bit.
The Raspberry Pi hardware doesn't support a proper software-initiated
shutdown, so this instead uses the watchdog to reboot to a special
partition which the firmware interprets as an immediate halt on
shutdown. When running under Qemu, this causes the emulator to exit.
These functions would have caused a `-Woverloaded-virtual` warning with
GCC 13, as they shadow `File::{attach,detach}(OpenFileDescription&)`.
Both of these functions had a single call site. This commit inlines
`attach` into its only caller, `FIFO::open_direction`.
Instead of explicitly checking `is_fifo()` in `~OpenFileDescription`
before running the `detach(Direction)` overload, let's just override the
regular `detach(OpenFileDescription&)` for `FIFO` to perform this action
instead.
Whenever an entry is added to the cache, the last element is removed to
make space for the new entry(if the cache is full). To make this an LRU
cache, the entry needs to be moved to the front of the list when there
is a cache hit so that the least recently used entry moves to the end
to be evicted first.
This was the last change that was needed to be able boot with the flag
of LOCK_IN_CRITICAL_DEBUG. That flag is not always enabled because there
are still other issues in which we hold a spinlock and still try to lock
a mutex.
Instead of using one global mutex we can protect internal structures of
the InodeWatcher class with SpinlockProtected wrappers. This in turn
allows the InodeWatcher code to be called from other parts in the kernel
while holding a prior spinlock properly.
`process.fds()` is protected by a Mutex, which causes issues when we try
to acquire it while holding a Spinlock. Since nothing seems to use this
value, let's just remove it entirely for now.
The existing `read_entire` is quite slow due to allocating and copying
multiple times, but it is simultaneously quite hard to get rid of in a
single step. As a replacement, add a new function that reads as much as
possible directly into a user-provided buffer.
To do this we also need to get rid of LockRefPtrs in the USB code as
well.
Most of the SysFS nodes are statically generated during boot and are not
mutated afterwards.
The same goes for general device code - once we generate the appropriate
SysFS nodes, we almost never mutate the node pointers afterwards, making
locking unnecessary.
We have a problem with the original utimensat syscall because when we
do call LibC futimens function, internally we provide an empty path,
and the Kernel get_syscall_path_argument method will detect this as an
invalid path.
This happens to spit an error for example in the touch utility, so if a
user is running "touch non_existing_file", it will create that file, but
the user will still see an error coming from LibC futimens function.
This new syscall gets an open file description and it provides the same
functionality as utimensat, on the specified open file description.
The new syscall will be used later by LibC to properly implement LibC
futimens function so the situation described with relation to the
"touch" utility could be fixed.
These were easy to pick-up as these pointers are assigned during the
construction point and are never changed afterwards.
This small change to these pointers will ensure that our code will not
accidentally assign these pointers with a new object which is always a
kind of bug we will want to prevent.
These were stored in a bunch of places. The main one that's a bit iffy
is the Mutex::m_holder one, which I'm going to simplify in a subsequent
commit.
In Plan9FS and WorkQueue, we can't make the NNRPs const due to
initialization order problems. That's probably doable with further
cleanup, but left as an exercise for our future selves.
Before starting this, I expected the thread blockers to be a problem,
but as it turns out they were super straightforward (for once!) as they
don't mutate the thread after initiating a block, so they can just use
simple const-ified NNRPs.
- Instead of taking the first new thread as an out-parameter, we now
bundle the process and its first thread in a struct and use that
as the return value.
- Make all Process factory functions return ErrorOr. Use this to convert
some places to more TRY().
- Drop the "try_" prefix on Process factory functions.
The only persistent one of these was Thread::m_process and that never
changes after initialization. Make it const to enforce this and switch
everything over to RefPtr & NonnullRefPtr.
- The host custody never changes after initialization, so there's no
need to protect it with a spinlock.
- To enforce the fact that some members don't change after
initialization, make them const.
There was only one permanent storage location for these: as a member
in the Mount class.
That member is never modified after Mount initialization, so we don't
need to worry about races there.
This commit fixes a kernel panic that happened when unmounting
a disk due to an invalid memory access.
This was because `DiskCache` initializes two linked lists that use
an argument `KBuffer` as the storage for their elements.
Since the member `KBuffer` was declared after the two lists,
when `DiskCache`'s destructor was called, then `KBuffer`'s destructor
was called before the ones of the two lists, causing a page fault in
the kernel.
This is done with 2 major steps:
1. Remove JailManagement singleton and use a structure that resembles
what we have with the Process object. This is required later for the
second step in this commit, but on its own, is a major change that
removes this clunky singleton that had no real usage by itself.
2. Use IntrusiveLists to keep references to Process objects in the same
Jail so it will be much more straightforward to iterate on this kind
of objects when needed. Previously we locked the entire Process list
and we did a simple pointer comparison to check if the checked
Process we iterate on is in the same Jail or not, which required
taking multiple Spinlocks in a very clumsy and heavyweight way.
This was mostly straightforward, as all the storage locations are
guarded by some related mutex.
The use of old-school associated mutexes instead of MutexProtected
is unfortunate, but the process to modernize such code is ongoing.
This patch switches away from {Nonnull,}LockRefPtr to the non-locking
smart pointers throughout the kernel.
I've looked at the handful of places where these were being persisted
and I don't see any race situations.
Note that the process file descriptor table (Process::m_fds) was already
guarded via MutexProtected.
Before of this patch, we looked at the unveil data of the FinalizerTask,
which naturally doesn't have any unveil restrictions, therefore allowing
an unveil bypass for a process that enabled performance coredumps.
To ensure we always check the dumped process unveil data, an option to
pass a Process& has been added to a couple of methods in the class of
VirtualFileSystem.
Since the ProcFS doesn't hold many global objects within it, the need
for a fully-structured design of backing components and a registry like
with the SysFS is no longer true.
To acommodate this, let's remove all backing store and components of the
ProcFS, so now it resembles what we had in the early days of ProcFS in
the project - a mostly-static filesystem, with very small amount of
kmalloc allocations needed.
We still use the inode index mechanism to understand the role of each
inode, but this is done in a much "static"ier way than before.
This subdirectory is meant to hold all constant data related to the
kernel. This means that this data is never meant to updated and is
relevant from system boot to system shutdown.
Move the inodes of "load_base", "cmdline" and "system_mode" to that
directory. All nodes under this new subdirectory are generated during
boot, and therefore don't require calling kmalloc each time we need to
read them. Locking is also not necessary, because these nodes and their
data are completely static once being generated.
This is considered somewhat an abstraction layer violation, because we
should always let userspace to decide on the root filesystem mount flags
because it allows the user to configure the mount table to preferences
that they desire.
Now that SystemServer is modified to re-mount the root mount with the
desired flags, we can just mount the root filesystem without assuming
special flags.
The check of ensuring we are not trying to read beyond the end of the
inode data buffer is already there, it's just that we need to disallow
further reading if the read offset equals to the inode data size.
Apparently we lacked this important check from the beginning of this
piece of code. This check is crucial to ensure we only give back data
being related to the FATInode data buffer and nothing beyond it.
There was a bug in which bound Inodes would lose all their references
(because localsocket does not reference them), and they would be
deallocated, and clients would get ECONNREFUSED as a result. now
LocalSocket has a strong reference to inode so that the inode will live
as long as the socket, and Inode has a weak reference to the socket,
because if the socket stops being referenced anywhere it should not be
bound.
This still prevents the reference loop that
220b7dd779 was trying to fix.
This replaces manually grabbing the thread's main lock.
This lets us remove the `get_thread_name` and `set_thread_name` syscalls
from the big lock. :^)
This filesystem is based on the code of the long-lived TmpFS. It differs
from that filesystem in one keypoint - its root inode doesn't have a
sticky bit on it.
Therefore, we mount it on /dev, to ensure only root can modify files on
that directory. In addition to that, /tmp is mounted directly in the
SystemServer main (start) code, so it's no longer specified in the fstab
file. We ensure that /tmp has a sticky bit and has the value 0777 for
root directory permissions, which is certainly a special case when using
RAM-backed (and in general other) filesystems.
Because of these 2 changes, it's no longer needed to maintain the TmpFS
filesystem, hence it's removed (renamed to RAMFS), because the RAMFS
represents the purpose of this filesystem in a much better way - it
relies on being backed by RAM "storage", and therefore it's easy to
conclude it's temporary and volatile, so its content is gone on either
system shutdown or unmounting of the filesystem.
This is done by merging all scattered pieces of derived classes from the
ProcFSInode class into that one class, so we don't use inheritance but
rather simplistic checks to determine the proper code for each ProcFS
inode with its specific characteristics.
For each exposed PCI device in sysfs, there's a new node called "rom"
and by reading it, it exposes the raw data of a PCI option ROM blob to
a user for examining the blob.
There are now 2 separate classes for almost the same object type:
- EnumerableDeviceIdentifier, which is used in the enumeration code for
all PCI host controller classes. This is allowed to be moved and
copied, as it doesn't support ref-counting.
- DeviceIdentifier, which inherits from EnumerableDeviceIdentifier. This
class uses ref-counting, and is not allowed to be copied. It has a
spinlock member in its structure to allow safely executing complicated
IO sequences on a PCI device and its space configuration.
There's a static method that allows a quick conversion from
EnumerableDeviceIdentifier to DeviceIdentifier while creating a
NonnullRefPtr out of it.
The reason for doing this is for the sake of integrity and reliablity of
the system in 2 places:
- Ensure that "complicated" tasks that rely on manipulating PCI device
registers are done in a safe manner. For example, determining a PCI
BAR space size requires multiple read and writes to the same register,
and if another CPU tries to do something else with our selected
register, then the result will be a catastrophe.
- Allow the PCI API to have a united form around a shared object which
actually holds much more data than the PCI::Address structure. This is
fundamental if we want to do certain types of optimizations, and be
able to support more features of the PCI bus in the foreseeable
future.
This patch already has several implications:
- All PCI::Device(s) hold a reference to a DeviceIdentifier structure
being given originally from the PCI::Access singleton. This means that
all instances of DeviceIdentifier structures are located in one place,
and all references are pointing to that location. This ensures that
locking the operation spinlock will take effect in all the appropriate
places.
- We no longer support adding PCI host controllers and then immediately
allow for enumerating it with a lambda function. It was found that
this method is extremely broken and too much complicated to work
reliably with the new paradigm being introduced in this patch. This
means that for Volume Management Devices (Intel VMD devices), we
simply first enumerate the PCI bus for such devices in the storage
code, and if we find a device, we attach it in the PCI::Access method
which will scan for devices behind that bridge and will add new
DeviceIdentifier(s) objects to its internal Vector. Afterwards, we
just continue as usual with scanning for actual storage controllers,
so we will find a corresponding NVMe controllers if there were any
behind that VMD bridge.
A lot of places were relying on AK/Traits.h to give it strnlen, memcmp,
memcpy and other related declarations.
In the quest to remove inclusion of LibC headers from Kernel files, deal
with all the fallout of this included-everywhere header including less
things.
This header has always been fundamentally a Kernel API file. Move it
where it belongs. Include it directly in Kernel files, and make
Userland applications include it via sys/ioctl.h rather than directly.
Resolves issue where a panic would occur if the file system failed to
initialize or mount, due to how the FileSystem was already added to
VFS's list. The newly-created FileSystem destructor would fail as a
result of the object still remaining in the IntrusiveList.
We really don't want callers of this function to accidentally change
the jail, or even worse - remove the Process from an attached jail.
To ensure this never happens, we can just declare this method as const
so nobody can mutate it this way.
Use this helper function in various places to replace the old code of
acquiring the SpinlockProtected<RefPtr<Jail>> of a Process to do that
validation.
Only do so after a brief check if we are in a Jail or not. This fixes
SMP, because apparently it is crashing when calling try_generate()
from the SysFSGlobalInformation::refresh_data method, so the fix for
this is to simply not do that inside the Process' Jail spinlock scope,
because otherwise we will simply have a possible flow of taking
multiple conflicting Spinlocks (in the wrong order multiple times), for
the SysFSOverallProcesses generation code:
Process::current().jail(), and then Process::for_each_in_same_jail being
called, we take Process::all_instances(), and Process::current().jail()
again.
Therefore, we should at the very least eliminate the first taking of the
Process::current().jail() spinlock, in the refresh_data method of the
SysFSGlobalInformation class.
* Fix bug where last character of a filename or extension would be
truncated (HELLO.TXT -> HELL.TX).
* Fix bug where additional NULL characters would be added to long
filenames that did not completely fill one of the Long Filename Entry
character fields.
These instances were detected by searching for files that include
AK/Memory.h, but don't match the regex:
\\b(fast_u32_copy|fast_u32_fill|secure_zero|timing_safe_compare)\\b
This regex is pessimistic, so there might be more files that don't
actually use any memory function.
In theory, one might use LibCPP to detect things like this
automatically, but let's do this one step after another.
These instances were detected by searching for files that include
Kernel/Debug.h, but don't match the regex:
\\bdbgln_if\(|_DEBUG\\b
This regex is pessimistic, so there might be more files that don't check
for any real *_DEBUG macro. There seem to be no corner cases anyway.
In theory, one might use LibCPP to detect things like this
automatically, but let's do this one step after another.
This step would ideally not have been necessary (increases amount of
refactoring and templates necessary, which in turn increases build
times), but it gives us a couple of nice properties:
- SpinlockProtected inside Singleton (a very common combination) can now
obtain any lock rank just via the template parameter. It was not
previously possible to do this with SingletonInstanceCreator magic.
- SpinlockProtected's lock rank is now mandatory; this is the majority
of cases and allows us to see where we're still missing proper ranks.
- The type already informs us what lock rank a lock has, which aids code
readability and (possibly, if gdb cooperates) lock mismatch debugging.
- The rank of a lock can no longer be dynamic, which is not something we
wanted in the first place (or made use of). Locks randomly changing
their rank sounds like a disaster waiting to happen.
- In some places, we might be able to statically check that locks are
taken in the right order (with the right lock rank checking
implementation) as rank information is fully statically known.
This refactoring even more exposes the fact that Mutex has no lock rank
capabilites, which is not fixed here.
We were already handling the rmdir("..") case by refusing to remove
directories that were not empty.
This patch removes a FIXME from January 2019 and adds a test. :^)
Dr. POSIX says that we should reject attempts to rmdir() the file named
"." so this patch does exactly that. We also add a test.
This solves a FIXME from January 2019. :^)
This commit makes it possible for a process to downgrade a file lock it
holds from a write (exclusive) lock to a read (shared) lock. For this,
the process must point to the exact range of the flock, and must be the
owner of the lock.
The fact that we used a Vector meant that even if creating a Mount
object succeeded, we were still at a risk that appending to the actual
mounts Vector could fail due to OOM condition. To guard against this,
the mount table is now an IntrusiveList, which always means that when
allocation of a Mount object succeeded, then inserting that object to
the list will succeed, which allows us to fail early in case of OOM
condition.
This solves one of the security issues being mentioned in issue #15996.
We simply don't allow creating hardlinks on paths that were not unveiled
as writable to prevent possible bypass on a certain path that was
unveiled as non-writable.
Instead, allow userspace to decide on the coredump directory path. By
default, SystemServer sets it to the /tmp/coredump directory, but users
can now change this by writing a new path to the sysfs node at
/sys/kernel/variables/coredump_directory, and also to read this node to
check where coredumps are currently generated at.
By default, disallow reading of values in that directory. Later on, we
will enable sparingly read access to specific files.
The idea that led to this mechanism was suggested by Jean-Baptiste
Boric (also known as boricj in GitHub), to prevent access to sensitive
information in the SysFS if someone adds a new file in the /sys/kernel
directory.
There's simply no benefit in allowing sandboxed programs to change the
power state of the machine, so disallow writes to the mentioned node to
prevent malicious programs to request that.
To accomplish this, we add another VeilState which is called
LockedInherited. The idea is to apply exec unveil data, similar to
execpromises of the pledge syscall, on the current exec'ed program
during the execve sequence. When applying the forced unveil data, the
veil state is set to be locked but the special state of LockedInherited
ensures that if the new program tries to unveil paths, the request will
silently be ignored, so the program will continue running without
receiving an error, but is still can only use the paths that were
unveiled before the exec syscall. This in turn, allows us to use the
unveil syscall with a special utility to sandbox other userland programs
in terms of what is visible to them on the filesystem, and is usable on
both programs that use or don't use the unveil syscall in their code.
Because the ".." entry in a directory is a separate inode, if a
directory is renamed to a new location, then we should update this entry
the point to the new parent directory as well.
Co-authored-by: Liav A <liavalb@gmail.com>
Each GenericInterruptHandler now tracks the number of calls that each
CPU has serviced.
This takes care of a FIXME in the /sys/kernel/interrupts generator.
Also, the lsirq command line tool now displays per-CPU call counts.
Our implementation for Jails resembles much of how FreeBSD jails are
working - it's essentially only a matter of using a RefPtr in the
Process class to a Jail object. Then, when we iterate over all processes
in various cases, we could ensure if either the current process is in
jail and therefore should be restricted what is visible in terms of
PID isolation, and also to be able to expose metadata about Jails in
/sys/kernel/jails node (which does not reveal anything to a process
which is in jail).
A lifetime model for the Jail object is currently plain simple - there's
simpy no way to manually delete a Jail object once it was created. Such
feature should be carefully designed to allow safe destruction of a Jail
without the possibility of releasing a process which is in Jail from the
actual jail. Each process which is attached into a Jail cannot leave it
until the end of a Process (i.e. when finalizing a Process). All jails
are kept being referenced in the JailManagement. When a last attached
process is finalized, the Jail is automatically destroyed.
Let's put the power_state global node into the /sys/kernel directory,
because that directory represents all global nodes and variables being
related to the Kernel. It's also a mutable node, that is more acceptable
being in the mentioned directory due to the fact that all other files in
the /sys/firmware directory are just firmware blobs and are not mutable
at all.
The ProcFS is an utter mess currently, so let's start move things that
are not related to processes-info. To ensure it's done in a sane manner,
we start by duplicating all /proc/ global nodes to the /sys/kernel/
directory, then we will move Userland to use the new directory so the
old directory nodes can be removed from the /proc directory.
If a program needs to execute a dynamic executable program, then it
should unveil /usr/lib/Loader.so by itself and not rely on the Kernel to
allow using this binary without any sense of respect to unveil promises
being made by the running parent program.
Previously we didn't send the SIGPIPE signal to processes when
sendto()/sendmsg()/etc. returned EPIPE. And now we do.
This also adds support for MSG_NOSIGNAL to suppress the signal.
This commit reached that goal of "safely discarding" a filesystem by
doing the following:
1. Stop using the s_file_system_map HashMap as it was an unsafe measure
to access pointers of FileSystems. Instead, make sure to register all
FileSystems at the VFS layer, with an IntrusiveList, to avoid problems
related to OOM conditions.
2. Make sure to cleanly remove the DiskCache object from a BlockBased
filesystem, so the destructor of such object will not need to do that in
the destruction point.
3. For ext2 filesystems, don't cache the root inode at m_inode_cache
HashMap. The reason for this is that when unmounting an ext2 filesystem,
we lookup at the cache to see if there's a reference to a cached inode
and if that's the case, we fail with EBUSY. If we keep the m_root_inode
also being referenced at the m_inode_cache map, we have 2 references to
that object, which will lead to fail with EBUSY. Also, it's much simpler
to always ask for a root inode and get it immediately from m_root_inode,
instead of looking up the cache for that inode.
The idea is to enable mounting FileSystem objects across multiple mounts
in contrast to what happened until now - each mount has its own unique
FileSystem object being attached to it.
Considering a situation of mounting a block device at 2 different mount
points at in system, there were a couple of critical flaws due to how
the previous "design" worked:
1. BlockBasedFileSystem(s) that pointed to the same actual device had a
separate DiskCache object being attached to them. Because both instances
were not synchronized by any means, corruption of the filesystem is most
likely achieveable by a simple cache flush of either of the instances.
2. For superblock-oriented filesystems (such as the ext2 filesystem),
lack of synchronization between both instances can lead to severe
corruption in the superblock, which could render the entire filesystem
unusable.
3. Flags of a specific filesystem implementation (for example, with xfs
on Linux, one can instruct to mount it with the discard option) must be
honored across multiple mounts, to ensure expected behavior against a
particular filesystem.
This patch put the foundations to start fix the issues mentioned above.
However, there are still major issues to solve, so this is only a start.
