problem finding kernel address for a memory buffer

[Dave Zsiga <dzsiga@encore.com>]

I've got an application where a device driver is trying to translate a user 
memory buffer address into a kernel address.

The memory is allocated with shmget() because it is a shared memory segment 
shared by multiple processes.  The underlying allocation is kmalloc.

Sometimes my code works, but other times the maplist returned by a call to 
map_user_kiobuf() contains all zeros.  When the code is working, it continues 
working until after a reboot.

The user memory buffer is working properly in the process, but I can not  
access it from the driver.

unsigned int *buffer_address;  // address of user memory buffer
struct kiobuf *iobuf;

map_user_kiobuf(READ, iobuf, (unsigned long) buffer_address, 1);

When it fails, iobuf->maplist[0] == 0, iobuf->offset == 0, and 
page_address(iobuf->maplist[0]) == 0.

Can someone tell me what else I should be doing or checking?, or if there is 
more information I can provide to help fix this?

Dave Z.



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