On Tue, 4 Oct 2005, Brian Gerst wrote:
> Martin Drab wrote:
> > Hi,
> >
> > can anybody tell me why there is no sys_open() exported in kernel/ksyms.c in
> > 2.4 kernels while the sys_close() is there? And what is then the preferred
> > way of opening files from within a 2.4 kernel module?
>
> Why do you need to open files from kernel space? There are usually better
> alternatives like the firmware loader interface.
I was kind of working this out here a while ago. I am collecting data from
RTLinux driver (in Real-Time). I am filing DMA buffers and I need to
transfer their contents (preferably by mmap()ping) to the user space.
My first problem (that I was solving a while ago) was that I was unable to
mmap() the buffer using mmap() through the /dev/mem. I solved that by
creating my own device with its own fops->mmap() using vmops->nopage().
Problem is that this is not RT safe. So I wanted to do it all from
within the ioctl call to the RT-FIFOs, which are RT safe, since the
RT-FIFOs do not provide for the safe mmap() operation redefinition. I'm
not very sure it can be done in a safe way by calling the mmap() on that
new device from the user space.
Perhaps the only way then may be to do (from the user space):
0) read() from RT-FIFO the info about next available DMA buffer.
1) ioctl() to RT-FIFO to block the buffer and dispose it for the
user-space mmap() via the unsafe interface.
2) mmap() it from user space.
3) use the data from the mmap()ped buffer
4) munmap() the buffer.
5) ioctl() to the RT-FIFO to release the buffer for further reuse
Is that so?
Before I was kind of hoping I could do 2) from within 1) and 4) from
within 5), but evidently this was not a good idea.
Martin
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