I am working on linux epoll functionality for linuxlator. It implements
epoll through kqueue, but there is the need to overload fo_close
function in fileops to free some memory.
There is no generic mechanism defined in the kernel sources allowing to
do this, and it isn't desirable to do this in a hackish way. So I am
suggesting this particular way, see code snippets below.
This approach is inspired by how C++ classes are sub-classed, with C++
class being similar to kernel file descriptor type and C++ vtbl being
similar to fileops.
I am looking for an opinion(s) on these questions:
* Is such code is acceptable for kernel?
* Does it look too ugly?
* Any suggestions on how to improve it?
As the system develops, other places may require to do such overloading
too, so this approach can be reused.
Thank you,
Yuri
*** In sys/file.h add these macros (they define how overloading is done):
#define FDCLASS_DEFINE(cls) \
struct fileops* fdcls_##cls##_fileops(void); \
struct fileops* fdcls_##cls##_fileops(void) { \
return (&cls##ops); \
}
#define FDCLASS_INHERIT(cls, cls_parent, cls_init_func) \
extern struct fileops* fdcls_##cls_parent##_fileops(void); \
static void cls##_fdcls_init(void *dummy __unused) { \
cls##ops = *fdcls_##cls_parent##_fileops(); \
cls_init_func(); \
} \
SYSINIT(cls##_fdcls, SI_SUB_PSEUDO, SI_ORDER_ANY, cls##_fdcls_init,
NULL);
*** In the end of kern/kern_event.c add the line exposing kqueue's fileops:
FDCLASS_DEFINE(kqueue)
*** In linux_epoll.c add code that would initialize epoll fileops with
the base class fileops:
/* overload kqueue fileops */
static struct fileops epollops;
static struct fileops epollops_base;
static void
epoll_init(void) {
/* overload only fo_close operation */
epollops_base = epollops;
epollops.fo_close = epoll_close;
}
FDCLASS_INHERIT(epoll, kqueue, epoll_init)
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