On Thu, Nov 21, 2002 at 06:39:37PM -0500, Raghu R. Arur wrote:
> Hi,
>
> I have a problem. In my module I am not able to differentiate between
> whether requests are coming from a block device or character device.
>
> I am running my module on vmware and the keyboard hits are read thru
> ptty. The major number of ptty and the hard disk are both 3. I am blocking
> read system call in my module and I want to deal with the requests
> pertaining to the disk only. So given a file descriptor I am able to get
> the inode value and also the major and minor number of the device to which
> the request has to go.
>
> So in order to service only the requests of the disk i have an if
> statement
>
> if(inode && major == 3)
> {
> do my sys_read
> }
> else
> {
> do original sys_read
> }
>
>
> but every keystroke evaluates to true and does my sys_read section. I
> thought that character devices do not have inode and the ptty requests
> evaluate to false at if statement. But it is not happening so...
>
> am i missing something...
>
> please help me.
>
> thanks,
> raghu
Every device must have an inode. Actually sys_read is called on file and
file must have an inode. It is the device inode, that is it is the inode
that makes /dev/tty<n> appear on your filesystem (even if it may be
created on the fly by kernel, it's still an inode in memory). In this
inode, the i_dev should contain the device number and the i_mode should
contain the file type, in this case either IS_CHR(i_mode) or
IS_BLK(i_mode) should be true.
What about intercepting the function registered for char major 3?
Best way would be to patch the kernel a bit to make a hook there.
However if you find the file_operations structure registered for the
device, you can just replace the pointer in there.
PS: Please don't send new topics as a reply to unrelated message. Many
people have threaded mail readers and such mail tend to get lost in
threads.
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Jan 'Bulb' Hudec <bulb@ucw.cz>
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