Re: Copy_to_user and copy_from_user

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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Copy_to_user and copy_from_user

[Ramesh Sudini]

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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Re: Copy_to_user and copy_from_user

[Kernoulas]

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
>