Hi,

Bruno Prémont schrieb:

For USB-attached (or other hot-(un)pluggable) framebuffers the current
fbdev infrastructure is not very helpful. Each such driver currently
needs to perform the ref-counting on its own in .fbops.fb_open and
.fbops.fb_release callbacks.

I agree. This is a great idea even for non-hot-(un)pluggable framebuffers.

This patch moves the ref-counting in fbdev infrastructure.
(drivers have not been adjusted, all those releasing fb_info in
 .fbops.fb_destroy will not work -- patch for those will follow
 later on, all the others will continue to work fine)

API-wise the following changes are done:
- num_registered_fb and registered_fb variables are no more exported.
  New functions fb_get_registered() and fb_is_registered() replace
  them.
  The only know user of those was fbcon, thus the large diff on fbcon.c

  Note: the accesses to registered_fb and num_registered_fb look racy
  as there was not protection at all around them, potentially letting
  register_framebuffer() register two framebuffers on the same minor
  concurrently, fbcon access should have been safe by combination of
  its use of console_semaphore and reaction to events.
  In this patch I combined most of fbcon's accesses to registered_fb
  and num_registered_fb into fb_is_registered(), though I'm not sure
  if the num-check optimization is worth to keep or its check should
  be put into a separate function.

- framebuffer_release() is mapped to fb_put() but will go away
  when converting drivers

Reference count for fb_info can be increased with fb_get(fb_info) and
later released with fb_put(fb_info).


If you have concerns regarding the API changes, please let me know.

Uhm, I'm not really happy with what we count. With the old method you mentioned 
we ref-counted framebuffer users, after your patch it's more counting users + 
uses. This might be okay as we usually are interested whether the ref_count is 0 
or not but it doesn't look right if we modify the refcount during nearly every 
framebuffer operation. Wouldn't it be sufficient to do the refcounting in 
fb_open & fb_release operation + in fbcon where open&release are done?

As far as I know there exist framebuffer drivers which do not call 
framebuffer_alloc but contain their own fb_info. I guess these would be broken 
as well.


Thanks,

Florian Tobias Schandinat