Is vnode number also limit system-wide number of open file?

[ablacktshirt@gmail.com (Yubin Ruan)]

On Wed, May 31, 2017 at 01:30:59PM -0400, Rik van Riel wrote:
> On Wed, 2017-05-31 at 21:37 +0800, Yubin Ruan wrote:
> > I notice that there is a?
> > ????
> > 	unsigned long		i_ino;
> > 
> > in definition of `struct inode' [1], which is the virtual filesystem
> > inode.
> > Does that mean "inode number" and is it used for indexing in the
> > system-wide
> > inode table??
> > 
> > If that is the case, would that limit the number of open file in
> > Linux?
> 
> Those numbers are unrelated.
> 
> The i_ino number is the inode number within each
> filesystem, and different filesystems can have
> inodes with the same inode numbers.

Regarding to inode number, I notice that nearly every filesystem has tree
representation of the inode number:
    1. on-disk inode number
    2. in-memory inode number
    3. VFS inode number
How are these related? I mean, if they are all the same, then if filesystem A
and filesystem B both have some identical inode number, the VFS inode numbers
will conflict.
 
Yubin

> File descriptors (open files) point to a struct inode
> somewhere in memory. The same file can be opened many
> times (all programs opening libc.so). Many files will
> not be opened by any program at all.