Cloning 'struct file'

Prabhu nath gprabhunath at
Thu Jan 27 00:33:46 EST 2011

By experiment, we can know that all the fields of struct file are copied to
the child.
Here is what it happens.
When fork() is executed,
* A new array of struct file is created for the child.
* All the entries of the fd array of the parent is copied into the new array
of the child.
* Now both the parent and the child point to the same struct file pointer
for every opened
  file that has been opened before fork.
* f_count (file object's usage count) is incremented by 1, indicating that
there is one more
  task that is using this particular file object. This comes handy when a
task invokes
  close(), i.e. when close() function is invoked by any task, the kernel
just decrements this
  reference count. When the reference count is 0, VFS, invokes the release()
function of
  the driver associated with this file and frees the respective file object.

Hope this helps...


On Wed, Jan 26, 2011 at 4:29 PM, Daniel Baluta <daniel.baluta at>wrote:

> Hi all,
> We know that each file descriptor fd, has an associated 'struct file'. How
> is
> the 'struct file' copied/cloned at fork?
> Are all fields of 'struct file' inherited by child? I want to know if
> there is a function
> which takes a struct file* and creates a consistent copy/clone of it.
> thanks,
> Daniel.
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at
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