diff options
| author | Hans Verkuil | 2010-09-26 08:47:38 -0300 |
|---|---|---|
| committer | Mauro Carvalho Chehab | 2010-10-21 01:06:14 -0200 |
| commit | ee6869afc922a9849979e49bb3bbcad794872fcb (patch) | |
| tree | 2266050d01da694d04b533a6509873888327108b /Documentation/video4linux | |
| parent | c29fcff3daafbf46d64a543c1950bbd206ad8c1c (diff) | |
V4L/DVB: v4l2: add core serialization lock
Drivers can optionally set a pointer to a mutex in struct video_device.
The core will use that to lock before calling open, read, write, unlocked_ioctl,
poll, mmap or release.
Updated the documentation as well and ensure that v4l2-event knows about the
lock: it will unlock it before doing a blocking wait on an event and relock it
afterwards.
Ensure that the 'video_is_registered' check is done when the lock is held:
a typical disconnect will take the lock as well before unregistering the
device nodes, so to prevent race conditions the video_is_registered check
should also be done with the lock held.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Diffstat (limited to 'Documentation/video4linux')
| -rw-r--r-- | Documentation/video4linux/v4l2-framework.txt | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/Documentation/video4linux/v4l2-framework.txt b/Documentation/video4linux/v4l2-framework.txt index 9b1d81c26b7d..a128e012a45c 100644 --- a/Documentation/video4linux/v4l2-framework.txt +++ b/Documentation/video4linux/v4l2-framework.txt @@ -453,6 +453,10 @@ You should also set these fields: - ioctl_ops: if you use the v4l2_ioctl_ops to simplify ioctl maintenance (highly recommended to use this and it might become compulsory in the future!), then set this to your v4l2_ioctl_ops struct. +- lock: leave to NULL if you want to do all the locking in the driver. + Otherwise you give it a pointer to a struct mutex_lock and before any + of the v4l2_file_operations is called this lock will be taken by the + core and released afterwards. - parent: you only set this if v4l2_device was registered with NULL as the parent device struct. This only happens in cases where one hardware device has multiple PCI devices that all share the same v4l2_device core. @@ -469,6 +473,22 @@ If you use v4l2_ioctl_ops, then you should set either .unlocked_ioctl or The v4l2_file_operations struct is a subset of file_operations. The main difference is that the inode argument is omitted since it is never used. +v4l2_file_operations and locking +-------------------------------- + +You can set a pointer to a mutex_lock in struct video_device. Usually this +will be either a top-level mutex or a mutex per device node. If you want +finer-grained locking then you have to set it to NULL and do you own locking. + +If a lock is specified then all file operations will be serialized on that +lock. If you use videobuf then you must pass the same lock to the videobuf +queue initialize function: if videobuf has to wait for a frame to arrive, then +it will temporarily unlock the lock and relock it afterwards. If your driver +also waits in the code, then you should do the same to allow other processes +to access the device node while the first process is waiting for something. + +The implementation of a hotplug disconnect should also take the lock before +calling v4l2_device_disconnect and video_unregister_device. video_device registration ------------------------- |