Date: Fri, 25 Apr 2008 09:59:55 -0400 From: Adam <adamw@signallake.com> To: freebsd-hackers@freebsd.org Subject: CopyOut Size Limits Message-ID: <DAB770F2-C987-4AEB-BD02-BD1AEF099702@signallake.com>
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Hi, I am writing a custom system call that needs to transfer 16kb of
data from the kernel to userspace. I am transferring the data out of
the kernel by using copyout. This seems to work for a small struct of
data < 4k.
int my_system_call(struct thread *td, struct my_system_call_args *uap)
{
my_structtype_t my_type;
copyout(&my_type,uap->my_type,sizeof(my_type) ))!=0)
{
printf("\n copyout failed ret%d\n",error);
return error;
}
printf("exiting kernel %d\n",error);
return (0);
}
However once I expand my struct size beyond around 4k that I get a
"Fatal Double Fault." It seems like I am overrunning the kernel
stack. Does copyout use memory from the kernel stack? What is the
limit for copyout? Is there some way to allocate additional space?
Alternatively what is the appropriate method for transferring kbs of
data from kernel to userspace?
Thanks,
Adam
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