On Mon, 26 Jul 2004 Dhiman,Gaurav wrote : > >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 > Things work like this only. If you have 3 source files named 1.c 2.c 3.c and therez one variable to be shared among these 3, you need to make one .h say header.h where you put :- extern int SharedVariable; and in one of these 3 source files, you define it like this :- int SharedVariable; Now you can use it in any of these 3 files, but you have to include header.h in that file where you're using it... Thanks. Sumit Sharma, IBM. > > >-----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/ >
