On Sun, 13 Apr 2008, Arvin Moezzi wrote:
> On 4/11/08, Robert P. J. Day <rpjday@xxxxxxxxxxxxxx> wrote:
> >
> > from <linux/fs.h>:
> >
> > struct inode {
> >
> > ... snip ...
> >
> > struct list_head i_devices;
> > union {
> > struct pipe_inode_info *i_pipe;
> > struct block_device *i_bdev;
> > struct cdev *i_cdev;
> > };
> > int i_cindex;
> > ... snip ...
> > };
> >
> > so it's easy to see that an inode can hold at most one pointer to
> > one of a pipe, block dev or char dev structure. but, under normal
> > circumstances, when is that "i_cdev" field actually set to point
> > to the appropriate "struct cdev"?
>
> hi robert,
>
> I am not an expert but this is what i could read out of the kernel
> source: So whenever you try to open a file, the underlying
> filesystem is asked by the vfs to get the corresponding inode of
> that file. It is there where the routine "init_special_inode" (see
> for example in fs/ext2/inode.c:ext2_iget) is called which fills in
> the file_operations i_fop member of struct inode with "def_chr_fops"
> (note def_chr_ops.open = chrdev_open). Afterwards vfs calls the
> method i_fop.open (which points to chrdev_open, see fs/
> open.c:__dentry_open). In chrdev_open (as you already pointed out)
> then, if not already set due to some earlier opens, i_cdev is set
> depending on the i_rdev field.
yes, i eventually tracked down the same thing after perusing the code
more carefully. thanks.
rday
--
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry:
Have classroom, will lecture.
http://crashcourse.ca Waterloo, Ontario, CANADA
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