Noticed that mmap calls are failing for standard UVC V4L2 drivers (basic USB webcams) with the latest webcam commit.
This PR reverts changes from commit back to using O_RDWR flag for file open, and PROT_READ | PROT_WRITE flags for mmap calls.
This will allow the library to safely handle all standard v4l2 linux drivers. Even though we are not "writing", the v4l dev docs provide a warning about the requirement for read-write when streaming.
@bpstark Could you provide more details about locking out other processes? It is my understanding that unix.O_RDWR|unix.O_NONBLOCK file flags do not attach a file lock. We would need to explicitly call unix.Flock for that.
Testing
Tested on basic usb webcams that use uvc v4l2 driver (on a Raspberry Pi).
Happy to test out on other common v4l2 interfaces if that helps.
@bpstark Any specific testing I should do on loopbacks?
seanavery
commented
4 months ago
Description
Noticed that
mmapcalls are failing for standard UVC V4L2 drivers (basic USB webcams) with the latest webcam commit.This PR reverts changes from commit back to using
O_RDWRflag for file open, andPROT_READ | PROT_WRITEflags for mmap calls.This will allow the library to safely handle all standard v4l2 linux drivers. Even though we are not "writing", the v4l dev docs provide a warning about the requirement for read-write when streaming.
@bpstark Could you provide more details about locking out other processes? It is my understanding that
unix.O_RDWR|unix.O_NONBLOCKfile flags do not attach a file lock. We would need to explicitly callunix.Flockfor that.Testing