On Fri, 2006-05-19 at 07:01 -0700, UZAIR LAKHANI wrote:
> Hello All,
>
> Suppose I want to implement read/write file operations
> of a simple file system. Consider the read system
> call. The file system's struct file_operations
> function that will be called is this
>
> ssize_t (*read) (struct file *, char *, size_t, loff_t
> *);
>
> The char * in the arguments of read is a user-space
> buffer pointer. Suppose I don't want to send this
> buffer that we have got to the generic_file_read
> function or some other function and instead want to
> create a new buffer and send it to the
> generic_file_read (or other) function. Then copy this
> buffer that we have sent to the generic_file_read to
> the actual buffer that we had received so that the
> call can be completed and the buffer received is
> filled.
If you want to pass a kernel address to a function that takes a user
address, you need to call set_fs(KERNEL_DS) first. A few examples are
in fs/nfsd/vfs.c, such as:
oldfs = get_fs(); set_fs(KERNEL_DS);
err = inode->i_op->readlink(dentry, buf, *lenp);
set_fs(oldfs);
--
David Kleikamp
IBM Linux Technology Center
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