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SubjectRe: input: evdev.c EVIOCGRAB semantics question
Date
On Tuesday 15 August 2006 00:49, Magnus Vigerlöf wrote:
[...]
> However, this doesn't address the problem I initially described (I
> think)... What if two application open the same device and one of the
> application do a EVIOCGRAB. Should both applications still get events? With
> the above fix two applications that opens /dev/input/mouse2 resp
> /dev/input/event4 for the same hw and the latter grabs the device, both
> will get events. Using a counter for grab (just like the open-counter) on
> the handler should make them behave the same way in both cases I think.
> Gnnn... I'll make a patch tomorrow (ok today, Tuesday) so you can see what
> I rambling about..

Ok, this is what I mean (in code) if anyone's interested.. It should apply cleanly
on Dmitrys git-tree. It seems to work on my system without any side-effects
regarding the keyboard and Wacom tablet.

/Magnus

---
drivers/input/evdev.c | 41 +++++++++++++++++------------------------
1 files changed, 17 insertions(+), 24 deletions(-)
diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index 12c7ab8..c7e741b 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c
@@ -29,7 +29,7 @@ struct evdev {
char name[16];
struct input_handle handle;
wait_queue_head_t wait;
- struct evdev_list *grab;
+ int grab;
struct list_head list;
};

@@ -37,6 +37,7 @@ struct evdev_list {
struct input_event buffer[EVDEV_BUFFER_SIZE];
int head;
int tail;
+ int grab;
struct fasync_struct *fasync;
struct evdev *evdev;
struct list_head node;
@@ -49,8 +50,7 @@ static void evdev_event(struct input_han
struct evdev *evdev = handle->private;
struct evdev_list *list;

- if (evdev->grab) {
- list = evdev->grab;
+ list_for_each_entry(list, &evdev->list, node) {

do_gettimeofday(&list->buffer[list->head].time);
list->buffer[list->head].type = type;
@@ -59,17 +59,7 @@ static void evdev_event(struct input_han
list->head = (list->head + 1) & (EVDEV_BUFFER_SIZE - 1);

kill_fasync(&list->fasync, SIGIO, POLL_IN);
- } else
- list_for_each_entry(list, &evdev->list, node) {
-
- do_gettimeofday(&list->buffer[list->head].time);
- list->buffer[list->head].type = type;
- list->buffer[list->head].code = code;
- list->buffer[list->head].value = value;
- list->head = (list->head + 1) & (EVDEV_BUFFER_SIZE - 1);
-
- kill_fasync(&list->fasync, SIGIO, POLL_IN);
- }
+ }

wake_up_interruptible(&evdev->wait);
}
@@ -104,9 +94,10 @@ static int evdev_release(struct inode *
{
struct evdev_list *list = file->private_data;

- if (list->evdev->grab == list) {
- input_release_device(&list->evdev->handle);
- list->evdev->grab = NULL;
+ if (list->grab) {
+ if(!--list->evdev->grab && list->evdev->exist)
+ input_release_device(&list->evdev->handle);
+ list->grab = 0;
}

evdev_fasync(-1, file, 0);
@@ -483,17 +474,19 @@ static long evdev_ioctl_handler(struct f

case EVIOCGRAB:
if (p) {
- if (evdev->grab)
- return -EBUSY;
- if (input_grab_device(&evdev->handle))
+ if (list->grab)
return -EBUSY;
- evdev->grab = list;
+ if (!evdev->grab++)
+ if (input_grab_device(&evdev->handle))
+ return -EBUSY;
+ list->grab = 0;
return 0;
} else {
- if (evdev->grab != list)
+ if (!list->grab)
return -EINVAL;
- input_release_device(&evdev->handle);
- evdev->grab = NULL;
+ if (!--evdev->grab)
+ input_release_device(&evdev->handle);
+ list->grab = 0;
return 0;
}

-
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