Very Computer

Can I character device driver access or write to a file? I been told
NO.
If the answer is no please explain why.
If the answer is yes please explain how or where I can find more
information.

My background is writing device drivers for  Windows NT. It was hard
for me to believe that any device driver couldn't read/write to a
file.

John

It depends on the OS.  Some versions of UNIX make it easier than others.

RFM
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So you saying a character device driver can access a file? How about
Solaris or HP-UX?

Where can I get more information about this?

John

Quote:> So you saying a character device driver can access a file? How about
> Solaris or HP-UX?

> Where can I get more information about this?

http://docs.sun.com/db/doc/805-7378

--
Vladimir Ivanov

In Solaris, there is no public API for accessing files from the kernel.  
It's doable, but you've gotta roll your own functions.

It's been a few years since I've done anything with HP-UX so I can't
comment on that.

AIX and Linux both have kernel functions available for file I/O.

RFM
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And how would I do that? There's No kernel function to access a file?

Quote:>It's been a few years since I've done anything with HP-UX so I can't
>comment on that.

Currently I'm more interested in Solaris.

Quote:

>AIX and Linux both have kernel functions available for file I/O.

>RFM

Thank for the information. However, I didn't find any information how
a character device driver can access a file.

What I'm trying to do is access a file that contains driver
information. Similar to the way Windows NT has a registry that drivers
and applications can access.

John

I don't think you will find it generally possible in un*x as it's a layered system
where kernel mode is quite different from user-mode. ( you could say "It's DESIGNED" )

The "standard way" is to have a user-level utility/daemon do user-level stuff
like reading files etc. ioctl() is usually used for this.

Quote:> John

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Peter H?kanson        
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To retrieve the information from a driver's .conf file, see
the ddi_prop_op(9F) man pages.

If the config data doesn't fit in the .conf file format, then
like another poster said, have a configuration program read
the file, and pass it in through the device driver interface
using special ioctl or some such.

--
Andrew Gabriel
Consultant Software Engineer

In Solaris, driver configuration isn't done by directly reading a file.  
There's a conf file, and there are kernel functions to lookup the
properties that are specified in the file.  See the man pages for
driver.conf(4), ddi_prop_get_int(9F), and ddi_prop_lookup(9F) for
details.  Start here for an online discussion of these:

  http://docs.sun.com/db/doc/806-0633/6j9vn6q3i?a=view

Also, read chapter 4 in the "Writing Device Drivers" book.

As others have noted, the standard way for Unix kernel entities to access
a file is to have a user proxy do it for you.

RFM
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To reply, translate domain from l33+ 2p33|< to alpha.
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What started this discussion is that we have a PCI adaptor with
loadable firmware. This firmware changes the way the adaptor  behaves
(personality). Having 2 device driver, one to handle one personality
and the other to handle the other make it difficult to know which
adaptor goes with which driver.

The easiest way would be to create 1 device driver that handle both
personalities and with an ioctl call have the user change the adaptors
personality.

In windows NT, it was easy; just made an entry into the register. Made
a user program that allowed the user to modify the register to change
the adaptor from personality 1 to personality 2. The registry entry
was keyed on bus/slot number of the adaptor.

If personalities change during runtime, the driver.conf file probably isn't
the best approach.  If that's the case, the tactic is probably to write a
user program to send an ioctl to the driver directly.  There's not a good
way to asynchronously notify a kernel module of a change in a file.

Can the driver detect which firmware the adapter is operating with?

RFM
--
To reply, translate domain from l33+ 2p33|< to alpha.
                4=a  0=o  3=e  +=t

In solaris, the driver.conf(4) file is the analog of the Windows Registry.
I use it to turn debugging on and off in drivers, so I suspect it will
work for your purpose of distinguishing between two downloads. Just
define a property with an integer value. Access the property as described
in a prior posting.

Joseph Reuter
----------
In theory, theory and practice are the same;
in practice, they're not.

Quote:> Can I character device driver access or write to a file? I been told
> NO.

you've probably been told you *shouldn't* access files from kernel
mode, and it's generally true

Quote:> If the answer is no please explain why.

you should never put a text parser in kernel mode. All a device driver
should do is communicating with the hardware and other parts of the
system, and manipulate the simplest binary data possible. I see you
need a configuration file for your device - well, don't. Parse the
configuration file in an user-mode program, and pass the pre-parsed
data to the driver through a custom IOCTL

Quote:> My background is writing device drivers for  Windows NT. It was hard
> for me to believe that any device driver couldn't read/write to a
> file.

well, I don't know about Solaris, but in Windows NT, you can open files
from kernel mode. You open them with ZwCreateFile, and read from/write
to them with ZwReadFile/ZwWriteFile (all of which are documented in the
DDK) - not to mention you can build the IRPs by yourself (documented
too) for the maximum flexibility you could ask for