drm_read — read method for DRM file
ssize_t drm_read ( | struct file * filp, |
| char __user * buffer, | |
| size_t count, | |
loff_t * offset); |
filpfile pointer
bufferuserspace destination pointer for the read
countcount in bytes to read
offsetoffset to read
This function must be used by drivers as their .read #file_operations
method iff they use DRM events for asynchronous signalling to userspace.
Since events are used by the KMS API for vblank and page flip completion this
means all modern display drivers must use it.
offset is ignore, DRM events are read like a pipe. Therefore drivers also
must set the .llseek #file_operation to no_llseek. Polling support is
provided by drm_poll.
This function will only ever read a full event. Therefore userspace must supply a big enough buffer to fit any event to ensure forward progress. Since the maximum event space is currently 4K it's recommended to just use that for safety.