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ladybird/Kernel/Syscalls/disown.cpp

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Kernel+LibC: Add sys$disown() for disowning child processes This syscall allows a parent process to disown a child process, setting its parent PID to 0. Unparented processes are automatically reaped by the kernel upon exit, and no sys$waitid() is required. This will make it much nicer to do spawn-and-forget which is common in the GUI environment.
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/*
* Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
*
Everything: Move to SPDX license identifiers in all files. SPDX License Identifiers are a more compact / standardized way of representing file license information. See: https://spdx.dev/resources/use/#identifiers This was done with the `ambr` search and replace tool. ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
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* SPDX-License-Identifier: BSD-2-Clause
Kernel+LibC: Add sys$disown() for disowning child processes This syscall allows a parent process to disown a child process, setting its parent PID to 0. Unparented processes are automatically reaped by the kernel upon exit, and no sys$waitid() is required. This will make it much nicer to do spawn-and-forget which is common in the GUI environment.
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*/
#include <Kernel/Process.h>
namespace Kernel {
Kernel: Fix the return type for syscalls The Process::Handler type has KResultOr<FlatPtr> as its return type. Using a different return type with an equally-sized template parameter sort of works but breaks once that condition is no longer true, e.g. for KResultOr<int> on x86_64. Ideally the syscall handlers would also take FlatPtrs as their args so we can get rid of the reinterpret_cast for the function pointer but I didn't quite feel like cleaning that up as well.
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KResultOr<FlatPtr> Process::sys$disown(ProcessID pid)
Kernel+LibC: Add sys$disown() for disowning child processes This syscall allows a parent process to disown a child process, setting its parent PID to 0. Unparented processes are automatically reaped by the kernel upon exit, and no sys$waitid() is required. This will make it much nicer to do spawn-and-forget which is common in the GUI environment.
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{
Kernel: Annotate all syscalls with VERIFY_PROCESS_BIG_LOCK_ACQUIRED Before we start disabling acquisition of the big process lock for specific syscalls, make sure to document and assert that all the lock is held during all syscalls.
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VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this);
Kernel+LibC: Add sys$disown() for disowning child processes This syscall allows a parent process to disown a child process, setting its parent PID to 0. Unparented processes are automatically reaped by the kernel upon exit, and no sys$waitid() is required. This will make it much nicer to do spawn-and-forget which is common in the GUI environment.
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REQUIRE_PROMISE(proc);
auto process = Process::from_pid(pid);
if (!process)
Kernel: Make all syscall functions return KResultOr<T> This makes it a lot easier to return errors since we no longer have to worry about negating EFOO errors and can just return them flat.
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return ESRCH;
Kernel+LibC: Add sys$disown() for disowning child processes This syscall allows a parent process to disown a child process, setting its parent PID to 0. Unparented processes are automatically reaped by the kernel upon exit, and no sys$waitid() is required. This will make it much nicer to do spawn-and-forget which is common in the GUI environment.
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if (process->ppid() != this->pid())
Kernel: Make all syscall functions return KResultOr<T> This makes it a lot easier to return errors since we no longer have to worry about negating EFOO errors and can just return them flat.
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return ECHILD;
Kernel: Don't keep protected Process data in a separate allocation The previous architecture had a huge flaw: the pointer to the protected data was itself unprotected, allowing you to overwrite it at any time. This patch reorganizes the protected data so it's part of the Process class itself. (Actually, it's a new ProcessBase helper class.) We use the first 4 KB of Process objects themselves as the new storage location for protected data. Then we make Process objects page-aligned using MAKE_ALIGNED_ALLOCATED. This allows us to easily turn on/off write-protection for everything in the ProcessBase portion of Process. :^) Thanks to @bugaevc for pointing out the flaw! This is still not perfect but it's an improvement.
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ProtectedDataMutationScope scope(*process);
Kernel/Process: Move protected values to the end of the object The compiler can re-order the structure (class) members if that's necessary, so if we make Process to inherit from ProcFSExposedComponent, even if the declaration is to inherit first from ProcessBase, then from ProcFSExposedComponent and last from Weakable<Process>, the members of class ProcFSExposedComponent (including the Ref-counted parts) are the first members of the Process class. This problem made it impossible to safely use the current toggling method with the write-protection bit on the ProcessBase members, so instead of inheriting from it, we make its members the last ones in the Process class so we can safely locate and modify the corresponding page write protection bit of these values. We make sure that the Process class doesn't expand beyond 8192 bytes and the protected values are always aligned on a page boundary.
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process->m_protected_values.ppid = 0;
Kernel: disown should unblock any potential waiters This is necessary because if a process changes the state to Stopped or resumes from that state, a wait entry is created in the parent process. So, if a child process does this before disown is called, we need to clear those entries to avoid leaking references/zombies that won't be cleaned up until the former parent exits. This also should solve an even more unlikely corner case where another thread is waiting on a pid that is being disowned by another thread.
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process->disowned_by_waiter(*this);
Kernel+LibC: Add sys$disown() for disowning child processes This syscall allows a parent process to disown a child process, setting its parent PID to 0. Unparented processes are automatically reaped by the kernel upon exit, and no sys$waitid() is required. This will make it much nicer to do spawn-and-forget which is common in the GUI environment.
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return 0;
}
}
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