The CURRENT macro

The CURRENT macro

[Michael Zhu]

In Alessandro Rubini's book Linux Device Driver(Second
Edition), Chatper 12, he said that "By accessing the
fields in the request structure, usually by way of
CURRENT" and "CURRENT is just a pointer into
blk_dev[MAJOR_NR].request_queue". I know CURRENT is
just a macro. Where can I find the definition of this
macro?
I just don't know how to get the struct request from
the request_queue(a request_queue_t struct). CURRENT
points to which field in the
blk_dev[MAJOR_NR].request_queue? Thank you very much.

Michael

______________________________________________________ 
Send your holiday cheer with http://greetings.yahoo.ca

Re: The CURRENT macro

[Jonathan Corbet]

> In Alessandro Rubini's book Linux Device Driver(Second
> Edition), Chatper 12

Alessandro and...um...some other guy...:)

> he said that "By accessing the
> fields in the request structure, usually by way of
> CURRENT" and "CURRENT is just a pointer into
> blk_dev[MAJOR_NR].request_queue". I know CURRENT is
> just a macro. Where can I find the definition of this
> macro?

A little grepping in the source would give you the answer there.  It's in
.../include/linux/blk.h.  

> I just don't know how to get the struct request from
> the request_queue(a request_queue_t struct). CURRENT
> points to which field in the
> blk_dev[MAJOR_NR].request_queue? Thank you very much.

CURRENT is one way.  There's also functions like blkdev_entry_next_request
(also described in that chapter) that will pull a request off the queue for
you, if that's what you need.

Note that all this stuff has changed quite a bit in 2.5.

jon

Jonathan Corbet
Executive editor, LWN.net
corbet@lwn.net

Re: The CURRENT macro

[Arnaldo Carvalho de Melo]

Em Thu, Jan 03, 2002 at 02:48:39PM -0700, Jonathan Corbet escreveu:
> > In Alessandro Rubini's book Linux Device Driver(Second
> > Edition), Chatper 12

> Alessandro and...um...some other guy...:)

Yes, I know that other guy, very nice guy indeed 8)
 
> > he said that "By accessing the
> > fields in the request structure, usually by way of
> > CURRENT" and "CURRENT is just a pointer into
> > blk_dev[MAJOR_NR].request_queue". I know CURRENT is
> > just a macro. Where can I find the definition of this
> > macro?
 
> A little grepping in the source would give you the answer there.  It's in
> .../include/linux/blk.h.  

Or:

make tags
vi -t CURRENT 

8)

- Arnaldo

Re: The CURRENT macro

[Terje Eggestad]

On Thu, 2002-01-03 at 22:55, Arnaldo Carvalho de Melo wrote:

>  
> > A little grepping in the source would give you the answer there.  It's in
> > .../include/linux/blk.h.  
> 
> Or:
> 
> make tags
> vi -t CURRENT 
> 

Or 
make TAGS
emacs 
then in emacs: M-.


In either case make sure you do a make xconfig or another config to 
make sure tags are correct for your platform.


> 8)
> 
> - Arnaldo
> -
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TJ

Re: The CURRENT macro

[Richard B. Johnson]

On Thu, 3 Jan 2002, Michael Zhu wrote:

> In Alessandro Rubini's book Linux Device Driver(Second
> Edition), Chatper 12, he said that "By accessing the
> fields in the request structure, usually by way of
> CURRENT" and "CURRENT is just a pointer into
> blk_dev[MAJOR_NR].request_queue". I know CURRENT is
> just a macro. Where can I find the definition of this
> macro?
> I just don't know how to get the struct request from
> the request_queue(a request_queue_t struct). CURRENT
> points to which field in the
> blk_dev[MAJOR_NR].request_queue? Thank you very much.
> 
> Michael

If symlinks are set up:

/usr/include/linux/blk.h

#ifndef _BLK_H
#define _BLK_H

[SNIPPED...]

#ifndef CURRENT
#define CURRENT blkdev_entry_next_request(&blk_dev[MAJOR_NR].request_queue.queue_head)
#endif

#endif /* _BLK_H */

Otherwise:

../linux-n.n.n/include/linux/blk.h


FYI. To find things in the future, do:
cd /usr/include/linux
grep WHAT_TO_FIND *.h | more
cd ../asm
grep WHAT_TO_FIND *.h | more


Cheers,
Dick Johnson

Penguin : Linux version 2.4.1 on an i686 machine (797.90 BogoMips).

    I was going to compile a list of innovations that could be
    attributed to Microsoft. Once I realized that Ctrl-Alt-Del
    was handled in the BIOS, I found that there aren't any.

Re: The CURRENT macro

[Peter Makholm]

mylinuxk@yahoo.ca (Michael Zhu) writes:

> blk_dev[MAJOR_NR].request_queue". I know CURRENT is
> just a macro. Where can I find the definition of this
> macro?

Seek, and ye shall find (Matt 7.7):

xyzzy% find -type f | xargs grep "#define CURRENT "
./include/linux/blk.h:#define CURRENT blkdev_entry_next_request(&blk_dev[MAJOR_NR].request_queue.queue_head)
xyzzy%     

-- 
Når folk spørger mig, om jeg er nørd, bliver jeg altid ilde til mode
og svarer lidt undskyldende: "Nej, jeg bruger RedHat".
                                -- Allan Olesen på dk.edb.system.unix

Re: The CURRENT macro

[Tom Gall]

Michael Zhu wrote:
> 
> In Alessandro Rubini's book Linux Device Driver(Second
> Edition), Chatper 12, he said that "By accessing the
> fields in the request structure, usually by way of
> CURRENT" and "CURRENT is just a pointer into
> blk_dev[MAJOR_NR].request_queue". I know CURRENT is
> just a macro. Where can I find the definition of this
> macro?
> I just don't know how to get the struct request from
> the request_queue(a request_queue_t struct). CURRENT
> points to which field in the
> blk_dev[MAJOR_NR].request_queue? Thank you very much.

Look in include/asm-[your-arch]/current.h

It's architecture dependant. For instance on PPC64 we keep current in a
register.

Regards,

Tom

-- 
Tom Gall - [embedded] [PPC64 | PPC32] Code Monkey
Peace, Love &                  "Where's the ka-boom? There was
Linux Technology Center         supposed to be an earth
http://www.ibm.com/linux/ltc/   shattering ka-boom!"
(w) tom_gall@vnet.ibm.com       -- Marvin Martian
(w) 507-253-4558
(h) tgall@rochcivictheatre.org

Re: The CURRENT macro

[Tom Gall]

Michael Zhu wrote:
> 
> In Alessandro Rubini's book Linux Device Driver(Second
> Edition), Chatper 12, he said that "By accessing the
> fields in the request structure, usually by way of
> CURRENT" and "CURRENT is just a pointer into
> blk_dev[MAJOR_NR].request_queue". I know CURRENT is
> just a macro. Where can I find the definition of this
> macro?
> I just don't know how to get the struct request from
> the request_queue(a request_queue_t struct). CURRENT
> points to which field in the
> blk_dev[MAJOR_NR].request_queue? Thank you very much.

Heh!  Ignore that last one ...

Wrong current... you want CURRENT ... duh!  look in include/linux/blk.h

grep is your friend.

Regards,

Tom
-- 
Tom Gall - [embedded] [PPC64 | PPC32] Code Monkey
Peace, Love &                  "Where's the ka-boom? There was
Linux Technology Center         supposed to be an earth
http://www.ibm.com/linux/ltc/   shattering ka-boom!"
(w) tom_gall@vnet.ibm.com       -- Marvin Martian
(w) 507-253-4558
(h) tgall@rochcivictheatre.org