If you want to define the variable in kernel and use it in your driver, that variable should be exported, so that modules (like ur driver) can use it. Another thing is, never define a variable in header file, as header file will be included by number of .c files, so compiler will give "Multiple Definition" error. If a variable is going to be referred in number of .c files, the best practice is to define it in one .c file (it can be memory.c for your case, as you mentioned in your last mail) and declare the same variable in header file as extern. Now include this header file in all .c file where you want to refer that variable. Declaration of variable as extern, do not allocate a memory to variable. It is just a compiler directive statement, which tells the compiler that the variable has been defined in some other .c file so no need to give an error on finding reference to that variable. In your case, you can do following: memory.c: int bitmap = 0; EXPORT_SYMBOL(bitmap); something.h: extern int bitmap; your_driver.c #include <something.h> /*Any manipulation of bitmap*/ Bitmap += 1; I hope thing work like this, if I am wrong somewhere please correct me. Regards, Gaurav -----Original Message----- From: kernelnewbies-bounce@xxxxxxxxxxxx [mailto:kernelnewbies-bounce@xxxxxxxxxxxx] On Behalf Of Cristina Rivera Sent: Sunday, July 25, 2004 8:18 PM To: kernelnewbies@xxxxxxxxxxxx Subject: information between kernel and device driver Hi there, 3rd stage of my fight with the kernel. Problem: I have a char device which has to use information of a kernel variable (created for me) called bitmapped, this variable has to be used by the kernel to get information from user, I have thought about defining this variable in a header file for including it in the kernel, but...if my driver has to use it, can I define this variable in the code of my driver as extern if it's only defined at memory.c, for example? Which is the best way for defining this variable at the kernel and use it from either the kernel or the user? _________________________________________________________________ Descarga gratis la Barra de Herramientas de MSN http://www.msn.es/usuario/busqueda/barra?XAPID=2031&DI=1055&SU=http%3A// www.hotmail.com&HL=LINKTAG1OPENINGTEXT_MSNBH -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/ -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
