but i don't think that answers my question -- sure, i'll honour the
provided value, but what *is* that provided value by default? in
every example i've seen, it seems to be clear that that example will
work properly only if that original start offset is zero.
the code in fs/proc/devices.c is a good example. if that initial
offset was something other than zero, the output would be totally
screwed and miss printing some lines, no?
Yes, screwed 8^)
Consider an ordered array, If *pos != 0, you could return data using
*pos as a simple byte offset or you could use *pos as an element
offset into your array (it's up to you).
My usage right now involves returning arrayed kernel data expressed as
XML, I allow for the user to skip into the array (by elements) if they
choose to on some tables and others I allow them only to start at the
beginning. In these cases, if *pos != 0, I return NULL (for the
start*() methods).
If the next*() method is offset past the end of my array, I return
NULL, otherwise I increment *pos (as most generic examples will show).
*pos is really just a tool for the user. If you want your data to
behave as a "normal" block file, you have the onus to provide the
mechanism for indexing into your data with *pos and maintain the
position of *pos. Expect the unexpected. If I recall correctly,
perusing the source code for seq_file (it's a real mess!) shows that
*pos is not forced to zero.
-Bruce
rday
--
=
=
======================================================================
Robert P. J. Day Waterloo, Ontario,
CANADA
Linux Consulting, Training and Annoying Kernel Pedantry.
Web page: http://crashcourse.ca
Twitter: http://twitter.com/rpjday
"Kernel Newbie Corner" column @ linux.com: http://cli.gs/WG6WYX
=
=
======================================================================
