Re: Copy_to_user and copy_from_user

[Ramesh Sudini]

Then, how do I make sure that all the data I wanted to be copied is infact 
copied?? What are the scenarios where copy_to/from_user could fail and how 
can I avoid it.

Thanks
-Ramesh


> No you cannot call it until all data has been copied. copy_{to,from}_user 
> fails when a fault happens during the copy process. So you simply cannot 
> try again... It will fault again.
> Well, not 100% true. An other running thread (same mm with the process 
> which copies data) can "fix" the faulty adress space. Bad thread....
>
> Ramesh Sudini wrote:
> > Hi,
> >
> > If copy_from_user returns non zero value, then I do not see any driver(for 
> > example PPP) try to copy the remaining data. It treats it as an error 
> > scenario.
> >
> > Why is this? Shouldnt it have a while loop and attempt to copy_from_user 
> > till all the data is copied??
> >
> > I am writing a driver and trying to understand what needs to be done in 
> > case it returns a non-zero value? I have huge amount of data to be copied 
> > from user space Ex: 3000byte messages.
> >
> > Can somebody suggest me what is the best I could do...(Please cc me 
> > personally with your response)
> >
> > Thanks
> > Ramesh

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