On Fri, May 19, 2006 at 07:01:48 -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
Particularly to generic_file_read you **DO** want to pass it --
generic_file_read takes a user-space address just like the read file
operation. In fact some filesystems assign generic_file_read directly to
their read file operation slot.
> create a new buffer and send it to the
> generic_file_read (or other) function. Then copy this
Just have a look in any other filesystem. Does it do anything like that?!?!
> 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.
>
> Consider what I am doing now is
>
> static ssize_t
> foo_read(file_t *file, char *buf, size_t count, loff_t
> *ppos)
> {
> ...
> char __user local_buffer[10]; //TODO
> count = 10; // setting a new count
>
> // read_XXX below is to be taken as a function that
> // will do read for us e.g. generic_file_read can be
> // such a function
> err = read_XXX( file, local_buffer, count, ppos);
>
> // now copy local_buffer into buf
> ...
>
> // the err is -14 or BAD ADDRESS
> return err;
> }
>
> Any help regrading this is welcome.
>
> Thanks,
> Uzair Lakhani,
> Karachi, Pakistan.
>
>
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--
Jan 'Bulb' Hudec <bulb@xxxxxx>
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