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.
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.
diff --git a/drivers/video/fbsysfs.c b/drivers/video/fbsysfs.c
index 0a08f13..be5f342 100644
--- a/drivers/video/fbsysfs.c
+++ b/drivers/video/fbsysfs.c
@@ -58,6 +58,7 @@ struct fb_info *framebuffer_alloc(size_t size, struct device *dev)
info->par = p + fb_info_size;
info->device = dev;
+ kref_init(&info->refcount);