This project shows a simple example of using userfaultfd with minor faults on shared memory (UFFD_FEATURE_MINOR_SHMEM). I create two virtual memory ranges that both point to the same physical memory (backed by memfd) and register one of the virtual memory ranges with userfaultfd (UFFDIO_REGISTER_MODE_MINOR). I then access the registered virtual memory range and handle the generated userfaultfd page faults with the UFFDIO_CONTINUE ioctl.

Compile:

g++ main.cc -pthread -o main

Run:

./main

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The userfaultfd.h file included in this repository is the userfaultfd UAPI header from Linux v5.16. This is directly included in main.cc rather than <linux/userfaultfd.h>, which makes it easier to compile this project on a kernel that has out-of-date kernel headers.