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Kernel+Userland: Add ioctl to set process ownership of DisplayConnector
Now that the infrastructure of the Graphics subsystem is quite stable, it is time to try to fix a long-standing problem, which is the lack of locking on display connector devices. Reading and writing from multiple processes to a framebuffer controlled by the display connector is not a huge problem - it could be solved with POSIX locking. The real problem is some program that will try to do ioctl operations on a display connector without the WindowServer being aware of that which can lead to very bad situations, for example - assuming a framebuffer is encoded at a known resolution and certain display timings, but another process changed the ModeSetting of the display connector, leading to inconsistency on the properties of the current ModeSetting. To solve this, there's a new "master" ioctl to take "ownership" and another one to release that ownership of a display connector device. To ensure we will not hold a Process object forever just because it has an ownership over a display connector, we hold it with a weak reference, and if the process is gone, someone else can take an ownership.
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5 changed files with 101 additions and 8 deletions
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@ -148,6 +148,8 @@ private:
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virtual void will_be_destroyed() override;
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virtual void after_inserting() override;
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bool ioctl_requires_ownership(unsigned request) const;
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OwnPtr<Memory::Region> m_framebuffer_region;
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OwnPtr<Memory::Region> m_fake_writes_framebuffer_region;
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u8* m_framebuffer_data {};
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@ -162,6 +164,9 @@ protected:
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private:
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RefPtr<Memory::SharedFramebufferVMObject> m_shared_framebuffer_vmobject;
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WeakPtr<Process> m_responsible_process;
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Spinlock m_responsible_process_lock;
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IntrusiveListNode<DisplayConnector, RefPtr<DisplayConnector>> m_list_node;
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};
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}
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