Date: Sat, 26 Apr 2008 10:53:10 +0430 From: "H.fazaeli" <fazaeli@sepehrs.com> Cc: freebsd-hackers@freebsd.org Subject: Re: CopyOut Size Limits Message-ID: <4812CA4E.8030004@sepehrs.com> In-Reply-To: <DAB770F2-C987-4AEB-BD02-BD1AEF099702@signallake.com> References: <DAB770F2-C987-4AEB-BD02-BD1AEF099702@signallake.com>
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Do not allocate my_type (in general, big data structures) on kernel stack (e.g, use malloc(9)). Adam wrote: > 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 > > > > > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to > "freebsd-hackers-unsubscribe@freebsd.org" > > > -- With best regards. Hooman Fazaeli <fazaeli@sepehrs.com> Sepehr S. T. Co. Ltd. Web: http://www.sepehrs.com Tel: (9821)88975701-2 Fax: (9821)88983352
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