Gilles Chanteperdrix wrote: > Jan Kiszka wrote: >> Hi, >> >> a few changes of the RTDM layer were committed to trunk recently. They >> make handling of RTDM file descriptors more handy: >> >> o rt_dev_close/POSIX-close now polls as long as the underlying device >> reports -EAGAIN. No more looping inside the application is required. >> This applies to the usual non-RT invocation of close, the corner >> case "close from RT context" can still return EAGAIN. >> >> o Automatic cleanup of open file descriptors has been implemented. This >> is not yet the perfect design (*), but a straightforward approach to >> ease the cleanup after application crashes or other unexpected >> terminations. >> >> The code is still young, so testers are welcome. >> >> Jan >> >> >> (*) Actually, I would like to see generic per-process file descriptor >> tables one day, used by both the POSIX and the RTDM skin. The FD table >> should be obtained via xnshadow_ppd_get(). > > I agree for the file descriptor table, but I do not see why it should be > bound to xnshadow_ppd_get. The file descriptor table could be > implemented in an object like fashion, where the caller is responsible > to pass the same pointer to the creation, use and desctruction routines.
But where to get this pointer from when I enter, say, rtdm_ioctl on behalf of some process? The caller just passes an integer, the file descriptor. > This would allow, for example, to have a descriptor table for > kernel-space threads. Another feature that would be interesting for the I don't see the need to offer kernel threads private fd tables. They can perfectly continue to use a common, then kernel-only table. There are too few of those threads, and there is no clear concept of a process boundary in kernel space. > posix skin would be to have a callback called at process fork time in > order to duplicate the fd table. Ack. IIRC, this callback could also serve to solve the only consistency issue of the ipipe_get_ptd() approach. > > > But first this requires >> lock-less xnshadow_ppd_get() based on ipipe_get_ptd() to keep the >> overhead limited. Yet another story. > > xnshadow_ppd_get is already lockless, usual callers have to hold the > nklock for other reasons anyway. > OK, depends on the POV :). Mine is that the related RTDM services do not hold nklock and will never have to. Moreover, there is no need for locking design-wise, because per-process data cannot vanish under the caller unless the caller vanishes. The need currently only comes from the hashing-based lookup (reminds me of the WCET issues kernel futexes have...). Jan
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