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>A single call back for many files</H1
><P
> When a large number of almost identical files is used, it's
quite inconvenient to use a separate call back function for
each file. A better approach is to have a single call back
function that distinguishes between the files by using the
<TT
CLASS="STRUCTFIELD"
><I
>data</I
></TT
> field in <SPAN
CLASS="STRUCTNAME"
>struct
proc_dir_entry</SPAN
>. First of all, the
<TT
CLASS="STRUCTFIELD"
><I
>data</I
></TT
> field has to be initialised:
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><PRE
CLASS="PROGRAMLISTING"
>struct proc_dir_entry* entry;
struct my_file_data *file_data;
file_data = kmalloc(sizeof(struct my_file_data), GFP_KERNEL);
entry->data = file_data;
</PRE
></TD
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><P
> The <TT
CLASS="STRUCTFIELD"
><I
>data</I
></TT
> field is a <SPAN
CLASS="TYPE"
>void
*</SPAN
>, so it can be initialised with anything.
</P
><P
> Now that the <TT
CLASS="STRUCTFIELD"
><I
>data</I
></TT
> field is set, the
<TT
CLASS="FUNCTION"
>read_proc</TT
> and
<TT
CLASS="FUNCTION"
>write_proc</TT
> can use it to distinguish
between files because they get it passed into their
<TT
CLASS="PARAMETER"
><I
>data</I
></TT
> parameter:
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><PRE
CLASS="PROGRAMLISTING"
>int foo_read_func(char *page, char **start, off_t off,
int count, int *eof, void *data)
{
int len;
if(data == file_data) {
/* special case for this file */
} else {
/* normal processing */
}
return len;
}
</PRE
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><P
> Be sure to free the <TT
CLASS="STRUCTFIELD"
><I
>data</I
></TT
> data field
when removing the procfs entry.
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