52193857e2
Android uses ashmem for sharing memory regions. We are looking forward to migrating all usecases of ashmem to memfd so that we can possibly remove the ashmem driver in the future from staging while also benefiting from using memfd and contributing to it. Note staging drivers are also not ABI and generally can be removed at anytime. One of the main usecases Android has is the ability to create a region and mmap it as writeable, then add protection against making any "future" writes while keeping the existing already mmap'ed writeable-region active. This allows us to implement a usecase where receivers of the shared memory buffer can get a read-only view, while the sender continues to write to the buffer. See CursorWindow documentation in Android for more details: https://developer.android.com/reference/android/database/CursorWindow This usecase cannot be implemented with the existing F_SEAL_WRITE seal. To support the usecase, this patch adds a new F_SEAL_FUTURE_WRITE seal which prevents any future mmap and write syscalls from succeeding while keeping the existing mmap active. Verified with test program at: https://lore.kernel.org/patchwork/patch/1008117/ Backport link: https://lore.kernel.org/patchwork/patch/1014892/ Bug: 113362644 Change-Id: If7424db3b64372932d455f0219cd9df613fec1d4 Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Joel Fernandes <joelaf@google.com> |
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