Messages in this thread | | | Subject | [PATCH] 0/3 Add pselect/ppoll() | From | David Woodhouse <> | Date | Tue, 29 Nov 2005 00:57:17 +0000 |
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The following implementation of ppoll() and pselect() system calls depends on the architecture providing a TIF_RESTORE_SIGMASK flag in the thread_info.
These system calls have to change the signal mask during their operation, and signal handlers must be invoked using the new, temporary signal mask. The old signal mask must be restored either upon successful exit from the system call, or upon returning from the invoked signal handler if the system call is interrupted. We can't simply restore the original signal mask and return to userspace, since the restored signal mask may actually block the signal which interrupted the system call.
The TIF_RESTORE_SIGMASK flag deals with this by causing the syscall exit path to trap into do_signal() just as TIF_SIGPENDING does, and by causing do_signal() to use the saved signal mask instead of the current signal mask when setting up the stack frame for the signal handler -- or by causing do_signal() to simply restore the saved signal mask in the case where there is no handler to be invoked.
The first patch implements the sys_pselect() and sys_ppoll() system calls, which are present only if TIF_RESTORE_SIGMASK is defined. That #ifdef should go away in time when all architectures have implemented it. The second patch implements TIF_RESTORE_SIGMASK for the PowerPC kernel (in the -mm tree), and the third patch then removes the arch-specific implementations of sys_rt_sigsuspend() and replaces them with generic versions using the same trick.
-- dwmw2
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