SYNOPSIS

ssize_t drm_read(struct file * filp, char __user * buffer, size_t count, loff_t * offset);

ARGUMENTS

filp

file pointer

buffer

userspace destination pointer for the read

count

count in bytes to read

offset

offset to read

DESCRIPTION

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.

RETURNS

Number of bytes read (always aligned to full events, and can be 0) or a negative error code on failure.

AUTHORS

Jesse Barnes <[email protected]>
Intel Corporation,         
        

Initial version

Laurent Pinchart <[email protected]>
Ideas on board SPRL,         
        

Driver internals

Daniel Vetter <[email protected]>
Intel Corporation,         
        

Contributions all over the place

Lukas Wunner <[email protected]>

vga_switcheroo documentation

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