Where does kernel store per task file position?

Rajat Sharma fs.rajat at gmail.com
Wed Jan 30 00:46:16 EST 2013

> I'm still not able to figure out where exactly is the position of file
stored per task_struct.
struct file * itself is per process (task_struct) so file->f_pos is file
position per process, if thats what you are looking for. I hope you haven't
assumed that struct file itself is unique for a file, i.e. per inode? Then
that assumption is wrong.


On Tue, Jan 29, 2013 at 6:38 PM, Pranay Kumar Srivastava <
Pranay.Shrivastava at hcl.com> wrote:

> Hi Everyone,
> I was trying to find out where does Linux store per process file position?
> Since struct file is allocated once when the file is first opened
> (get_empty_filp() via do_sys_open) .I looked at these,
> Copy_process--->copy_files-->dup_fd  it seemed to allocate only (struct
> file*)
> struct files_struct , but I couldn't find any field that is actually being
> used to store the file position.
> I'm still not able to figure out where exactly is the position of file
> stored per task_struct. Secondly even if this was being saved does the
> kernel changes f_pos of struct file whenever a (read/write) is done? I
> don't that happens [Correct?].
> Regards,
> Pranay Kumar Srivastava
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