The problem I have is that I don't want to grab the offset from
tsio_open() and store it in a static int as that would not allow
simultaneous opens of different ports.
I am now using filp->private_data to hold the minor and them accessing
it to find the offset within each tsio_read() / tsio_write(), but that
seems akward. Does anyone have a suggestion as to a better way to do
this or an explanation as to why I can't MINOR(inode->i_rdev) within
the read / write operations themselves?
Usually what is done is in open() call, the open call allocates a
structure, and places a pointer to that structure in filp->private_data.
This allows the driver to store various bits of state information,
either pre-calculated at device open time, or for state information
which is associated with the open file descriptor.
If you *only* need the I/O port offset, and you're willing to calculate
it each time in the read() and write() call, you can get access to the
inode from those functions. Just reference it as filp->f_dentry->d_inode.
So for example you can get the minor number by calculating
MINOR(filp->f_dentry->d_inode).
Hope this helps!
- Ted
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