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.
hope it is now a little bit clearer to you
arvin
--
To unsubscribe from this list: send an email with
"unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx
Please read the FAQ at http://kernelnewbies.org/FAQ
