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Jan 31, 2026
On certain devices (specifically observed on Android 12, arm32), the previous method of transferring the mount namespace failed with: `open mount namespace path [/proc/xxx/fd/y] failed with 13: Permission denied`. This commit refactors the namespace transfer mechanism to use direct File Descriptor passing via Unix domain sockets (SCM_RIGHTS). Changes: - Replaced the protocol: The daemon now sends a status byte followed immediately by the FD using `send_fd`, rather than sending the PID and raw FD integer. - The client no longer constructs a `/proc/...` string or calls `open()`. It receives the FD directly and passes it to `setns()`. - Added a status byte check to the protocol to prevent stream desynchronization when the namespace is not cached.
Needed on Android 12, kernel 3.4.113
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On some device (Android 12, arm 32 bit), the mount namespace transfer could fail due to permission denial.
We should thus implement a fallback mechanism of namespace transfer.