User space function execution from a kernel context for input/output filtering from a thread executing in the user space

A method comprising:

• initializing, by an operating system from a thread executing on a computing device, a second kernel stack separate from a first kernel stack, the operating system having a user space and a kernel space;
• performing, by the operating system from the thread executing in the kernel space using the first kernel stack, a non-blocking upcall to execute a function in the user space, wherein performing the non-blocking upcall comprises filtering one or more input/output (I/O) requests from the same thread in the user space;
• responsive to the function executing in the user space, performing at least one additional function in the kernel space using the initialized second kernel stack;
• and
• upon completion of the upcall, continuing execution of the same thread in the kernel space using the first kernel stack, wherein continuing execution of the thread comprises issuing the filtered one or more I/O requests down storage layers in the kernel space, and wherein filtered I/O completions are completed up the storage layers in the kernel space.

One or more computer-readable storage media including computer-executable instructions that, when executed, cause at least one processor to perform synchronous execution of a user space operation without a thread switch from a kernel context by:

• initializing, by an operating system executing on a computing device, an upcall mode from a user space for a thread;
• allocating an upcall kernel stack, separate from a current kernel stack, in response to initializing the upcall mode;
• performing, by the operating system on demand from the same thread from kernel space, an upcall function in the user space, wherein execution of the upcall function in the user space comprises filtering one or more input/output (I/O) requests from the thread using a user space stack, and wherein the operating system executes, using the allocated upcall kernel stack, kernel space functions generated by the upcall function;
• and
• returning to the kernel space upon completion of the upcall function to perform another function from the same thread in the kernel space using the current kernel stack, wherein performing the another function comprises issuing the filtered one or more I/O requests further down storage layers in the kernel space, and wherein filtered I/O completions are completed further up the storage layers in the kernel space.