Re: Accessing file from drivers (fwd)

Re: Accessing file from drivers (fwd)

[Soumya Desai]

>

Hi Wolfgang,

     The exact problem that we're trying to solve, is to program an FPGA with a hex file
which is in our file system.  But the problem is general is to have a way to write  a
system  call  say 'sys_copy'  which will copy one file to another.  An user-mode
application would read from one file and write back to another, which would result in
copying  the data from the file driver ( kernel space ) to the user-space,  and again
back to the kernel space.  We were curious as to whether a way existed by which we can
do the read and write, sitting in the kernel space itself.  Of course adding our own
ioctl to the drivers will serve the purpose,  but we were looking for some way in which
we would NOT need to modify the existing file system drivers.  I was wondering if it
would be possible to bypass the read/write call themselves, but hack our way into the
buffer caches of block drivers, to do this ?   Anyone tried something similar ?

Regards,
Soumya.

>
> ---------- Forwarded message ----------
> Date: Thu, 15 Mar 2001 15:04:31 +0100
> From: Wolfgang Denk <wd@denx.de>
> To: gopi@tejasnetworks.com
> Cc: linuxppc-dev@lists.linuxppc.org
> Subject: Re: Accessing file from drivers
>
> In message <Pine.LNX.4.21.0103151822090.9108-100000@localhost.localdomain> you wrote:
> >
> >   Is it possible to read and write to files (say /etc/xyz)
> > in a device driver without resorting to user space?  I want
>
> You do not want to do this. It's bad design. Implement an ioctl() for
> the configuration, and use that.
>
> Wolfgang Denk
>
> --
> Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
> Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
> "Send lawyers, guns and money..."  - Lyrics from a Warren Zevon song


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RE: Accessing file from drivers (fwd)

[Stefano Coluccini]

> Hi Wolfgang,
>
>      The exact problem that we're trying to solve, is to program
> an FPGA with a hex file
> which is in our file system.  But the problem is general is to
> have a way to write  a
> system  call  say 'sys_copy'  which will copy one file to
> another.  An user-mode
> application would read from one file and write back to another,
> which would result in
> copying  the data from the file driver ( kernel space ) to the
> user-space,  and again
> back to the kernel space.  We were curious as to whether a way
> existed by which we can
> do the read and write, sitting in the kernel space itself.

I don't know if I well understand the problem, but it seems to me that you
can use the mmap system call ...


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Re: Accessing file from drivers (fwd)

[Wolfgang Denk]

Dear Soumya,

in message <3AB1A57E.669B3166@tejasnetworks.com> you wrote:
>
>      The exact problem that we're trying to solve, is to program an FPGA with a hex file
> which is in our file system.  But the problem is general is to have a way to write  a

I thought it was something like that. The conventional way  to  solve
this  is  implementing  an  ioctl() call for this function, and use a
user-space program to select the file and feed it into the driver.

> system  call  say 'sys_copy'  which will copy one file to another.  An user-mode
> application would read from one file and write back to another, which would result in
> copying  the data from the file driver ( kernel space ) to the user-space,  and again
> back to the kernel space.  We were curious as to whether a way existed by which we can
> do the read and write, sitting in the kernel space itself.  Of course adding our own

Why do you want to do that? Is this such atime-critical operation? Of
course it's possible to implement such a function, but I'm  not  sure
if it really makes sense.

> ioctl to the drivers will serve the purpose,  but we were looking for some way in which
> we would NOT need to modify the existing file system drivers.  I was wondering if it

Ummm... I don't understand this sentence. Adding an ioctl() for  YOUR
OWN  driver  to  accept  a  buffer with FPGA image date and load that
image into the FLGA does not mean you have to modify  anything  else.
You just have to write a small user application which opens the file,
reads or mmap()s it, and calls that ioctl().

> would be possible to bypass the read/write call themselves, but hack our way into the
> buffer caches of block drivers, to do this ?   Anyone tried something similar ?

Possible? Sure it's possible. But there is some effort involved,  and
your  resulting  solution  is  probably very restricted to a specific
setup. What do you want to save that you are willing to  pay  such  a
price for?

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
I have the simplest tastes.  I am always satisfied with the best.
                                                       -- Oscar Wilde

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