Thanks Valdis.
Yes , custom kernel module has struct proto_ops pointing to the routines
in the module.
in the module.
my kernel module routines do not cal any of linux provided socket* calls.
it gets data from different app and provide that data back to app calling socket* APIs.
i understand linux kernel calls 32 bit version of syscall handler from sys call table .
but how do i do this in custom kernel module.
how to differentiate 32 bit and 64 app in my kernel module.
do i need all stuff from compat.h and compat.c (if i use same files will that work) ?
do i need to change some files in std kernel files too like syscall_32.tbl file , and recompile kernel ?
It would be great if there is any example / any web links for this to understad
Thanks
On Wed, Jan 4, 2017 at 10:10 AM, <Valdis.Kletnieks@xxxxxx> wrote:
On Wed, 04 Jan 2017 09:34:58 +0530, Pradeepa Kumar said:
> I have a custom kernel module providing new protocol and providing socket system calls.
In general, a loadable module can provide a new protocol, but can't add new
syscalls. However, adding support for socket(), connect(), recvmsg() and
so on for a new protocol *can* be done from a module, as long as the
protocol provides a suitable struct proto_ops pointing to the routines
in the module.
> i am seeing issues when 32 bit app runs (for exp recvmsg() call does not
> work if msg has cmsghdrs as struct size of cmsghdr is different in 32 bit
> and 64 bit).
That's a good reason to double-check your code to ensure that you don't
make that same mistake.
> This is because my custom kernel module does not have 32 bit compatibility
> layer ( but linux kernel has this in compat.c etc).
Hold that thought.
> is it simple to add compatibility layer to my custom kernel module
Given your previous sentence, you should be able to figure that out.
> how do i do this (any links ?)
/*
* linux/kernel/compat.c
*
* Kernel compatibililty routines for e.g. 32 bit syscall support
* on 64 bit kernels.
*
* Copyright (C) 2002-2003 Stephen Rothwell, IBM Corporation
May already have the functions you need. If not, use the code as a guide
to writing the stuff you're still lacking.
Note that in particular, recvmsg() combatability is already done for you via
this chunk of code in net/compat.c:
COMPAT_SYSCALL_DEFINE3(recvmsg, int, fd, struct compat_msghdr __user *, msg, unsigned int, flags)
{
return __sys_recvmsg(fd, (struct user_msghdr __user *)msg, flags | MSG_CMSG_COMPAT);
}
Go look and see what the MSG_CMSG_COMPAT flag does if you want the gory details.
_______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
