grep -r sched_fair.c sched.c; see "kernel/sched.c",you will find that how sched_fair.c is used. #include "sched_stats.h" #include "sched_idletask.c" #include "sched_fair.c" #include "sched_rt.c" #ifdef CONFIG_SCHED_DEBUG # include "sched_debug.c" That 's clearly..... I don't think it is good programming manner. But it 's really in many places of kernel. ^-^ 2009/3/13 Sukanto Ghosh <sukanto.cse.iitb@xxxxxxxxx>: > I understand forward declaration ... But have a look at > kernel/sched_fair.c ... struct cfs_rq has been used a number of places > in it, but they don't even have a forward declaration of the > structure. The only header file that gets included is > linux/latencytop.h ... which doesn't includes any header that has a > forward declaration of struct cfs_rq. so, how does the compiler gives > no errors ? > > If I just assume that i am missing a place from where the structure > gets the forward declaration (forward declaration is in linux\sched.h > header) ... how are the fields of this structure being accessed > inside kernel/sched_fair.c ? > > Now, if I assume that somehow the compiler gets the complete > declaration of "struct cfs_rq" inside kernel/sched_fair.c ... then why > does the compiler complains when I try to write a kprobe module for > the a function "__enqueue_entity" of kernel/sched_fair.c which > accesses the fields of this structure. > > I can understand why the compiler is complaining but why doesn't it do > so for the kernel/sched_fair.c case ... > > What am I missing ? > > > On Thu, Mar 12, 2009 at 10:09 PM, Durga Prasad <writexdp@xxxxxxxxx> wrote: >> Look for 'forward declaration' of variables in C. >> You are telling the compiler that "I am declaring such a structure. >> Understand it when you encounter it" . >> - Durga >> >> ________________________________ >> From: Sukanto Ghosh <sukanto.cse.iitb@xxxxxxxxx> >> To: Nelson Castillo <nelsoneci@xxxxxxxxx>; Pei Lin <telent997@xxxxxxxxx> >> Cc: kernelnewbies <kernelnewbies@xxxxxxxxxxxx> >> Sent: Thursday, March 12, 2009 3:06:46 PM >> Subject: Re: structure definition in a .c file rather than .h file >> >> On Thu, Mar 12, 2009 at 11:58 AM, Nelson Castillo <nelsoneci@xxxxxxxxx> >> wrote: >>> On Thu, Mar 12, 2009 at 2:06 PM, Sukanto Ghosh >>> <sukanto.cse.iitb@xxxxxxxxx> wrote: >>>> Hi, >>>> >>>> The complete definition of structure cfs_rq is in a .c file >>>> (kernel/sched.c). In the head linux/sched.h it has been declared as >>>> "struct cfs_rq;" >>>> What is the purpose of doing so ? >>> >>> With this declaration in linux/sched.h you can make pointers of the >>> structure anywhere. All pointers have the same size thus it just >>> doesn't matter if you don't know the details of the structure. >>> >>> The idea of not exposing the structure is just encapsulation. It means >>> you shouldn't be touching those fields outside kernel/sched.c unless >>> you use one of the provided API functions to do so (if any). >>> >> >> exactly, and yet the fields have been used in kernel/sched_fair.c >> .... this is what confuses me >> >> >> -- >> Regards, >> Sukanto Ghosh >> >> -- >> To unsubscribe from this list: send an email with >> "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx >> Please read the FAQ at http://kernelnewbies.org/FAQ >> >> >> > > > > -- > Regards, > Sukanto Ghosh > -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
