Scull Driver - Read

[Pranay Srivastava]

Hi Sahil

On Sun, Mar 15, 2015 at 10:17 AM, sahil aggarwal <sahil.agg15 at gmail.com> wrote:
> hi all,
>
> Going through scull driver code, i see read function reads only till
> end of 1 quantum, so do kernel call read multiple times if count from
> q_pos exceeds quantum size limit.?
>
>
> Ref: ldd3.
>
> if(count > quantum - q_pos)
> count = quantum - q_pos;
> if(copy_to_user(buf, dptr->data[s_pos] + q_pos,count)){
> retval = -EFAULT;
> goto out;
> }

If you are not using the default read/write routines, then its up to
you to code that.

Kernel doesn't do multiple read calls. It'll do only what you asked it
for no more but it can do less. For example, a file is say 100 KiB and
you are reading say 4KiB in a loop when do you stop?

Simply put it's the user space application which is doing the looping
and repeatedly doing read calls because it assumes that file isn't
finished.

So again when do you stop reading from the file, without knowing size
of the file.?

> *f_pos += count;
> retval = count;
>
> Thanks
> Regards
>
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-- 
        ---P.K.S