On Sun, Nov 24, 2024 at 05:48:13PM +0800, Jinliang Zheng wrote:
> >
> > Short version: there are 3 different notions -
> > 1) file as a collection of data kept by filesystem. Such things as
> > contents, ownership, permissions, timestamps belong there.
> > 2) IO channel used to access one of (1). open(2) creates such;
> > things like current position in file, whether it's read-only or read-write
> > open, etc. belong there. It does not belong to a process - after fork(),
> > ...
>
> I'm sorry that I don't know much about the implementation of UNIX, but
> specific to the implementation of Linux, struct file is more like a
> combination of what you said 1) and 2).
This is incorrect. In Linux (and historical implementations of Unix)
struct file is precisely (2). The struct file has a pointer to a
struct dentry, which in turn has a pointer to a struct inode. So a
struct file *refers* to (1), but it is *not* (1).
- Ted
