Hi!
>Finally, using, for example,
> append="mem=125m"
>I can reserve the top 5 MB of memory in a 128 MB machine and then use it as
>shared memory "directly." There are techniques that allow using the same
>address for these blocks in both the kernel & user-land so data structures
>can contain valid pointers.
Indeed, been there done this...
I chose my method because it gave my kernel level handler the ability to
examine and approve/disapprove all changes made by User space before making
them. When you have SEVERAL TONS of machine sitting atop 6 hydraulic jacks
running 3000 PSI - with 2 to 4 humans inside (then there is the hydraulic
control loading system connected to the yoke/columns running at 1200 PSI
that 1 to 2 humans are holding on to/reclining against). It is always best
to be RIDICULOUSLY paranoid...
;-)
-----Original Message-----
From: Dresner, Norman A. [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, February 07, 2001 11:29 AM
To: 'Gearheart, Todd'; 'Stuart Hughes'
Cc: '[EMAIL PROTECTED]'
Subject: RE: [rtl] beginner question
Todd.
It's always seemed to me to be much safer and simpler to implement ioctl(2)
functions to get & set parameters or data blocks.
Also consider mmap(2) to give users access to kernel data segments (always a
risky proposition which is why I favor ioctl.
Finally, using, for example,
append="mem=125m"
I can reserve the top 5 MB of memory in a 128 MB machine and then use it as
shared memory "directly." There are techniques that allow using the same
address for these blocks in both the kernel & user-land so data structures
can contain valid pointers.
Norman Dresner
Fellow Systems Engineer
Radar Systems Engineering Department
Electronic Systems and Sensors Segment
Northrop Grumman Corporation
Baltimore-Washington International Airport
7323 Aviation Boulevard
Baltimore Maryland 21240
Voice: (410) 993 - 2096 Mornings; all-day voice-mail
(410) 969 - 8068 Afternoons with answering machine
FAX: (410) 993 - 8084 On-site
(410) 969 - 8068 Afternoons; call first to arrange
E-Mail: Mornings: [EMAIL PROTECTED]
Afternoons: [EMAIL PROTECTED]
> -----Original Message-----
> From: Gearheart, Todd [SMTP:[EMAIL PROTECTED]]
> Sent: Wednesday, February 07, 2001 11:15 AM
> To: 'Stuart Hughes'
> Cc: '[EMAIL PROTECTED]'
> Subject: RE: [rtl] beginner question
>
> You can also "access" private data in kernel address space from user mode
> programs, by employing a simple trick. A user program can request access
> to
> a section of private kernel address space (via fifos, shared memory, or
> whatever). Then a kernel module can copy the requested section of the
> kernel
> private address space "needed in user space" into shared memory. Then user
> mode program can view/modify the shared memory area and signal/indicate
> the
> change(s) made. Finally the kernel module can take care of "updating" the
> changes back into the kernel private address space (from the shared memory
> area).
>
> I was able to implement a similar "swapping technique" in my simulator
> application. It allows access to ALL kernel real-time storage from the
> user
> side as well...
>
> Regards,
> Todd Gearheart
>
> -----Original Message-----
> From: Stuart Hughes [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, February 07, 2001 7:43 AM
> To: Stefano Picerno
> Cc: [EMAIL PROTECTED]
> Subject: Re: [rtl] beginner question
>
>
> Stefano Picerno wrote:
> >
> > If I have two different realtime modules, can I access the address space
> > of one of them from the other?
> >
> > I mean, if task A have some private data at 0x1234578, can task B read
> the
> > same data at the same address?
>
> Yes, they occupy the same kernel address space.
>
> Regards, Stuart
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