Hi Pranay Well explained. Thank you. On 20 March 2015 at 11:46, Pranay Srivastava <pranjas@gmail.com> wrote:
Hi Sahil
On Sun, Mar 15, 2015 at 10:17 AM, sahil aggarwal <sahil.agg15@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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