Output on FreeBSD 13 with kms-drm from drm-v4.16 branch:

$ cc $(pkg-config gbm --cflags --libs) gbm_test.c && ./a.out
Stat #1: mode=e880
sync #1 test failed: 9, Bad file descriptor

I've updated the test program to see if gbm_bo_import works anyway. Also, what happens if you run the drm-v5.0 branch?

I've updated the test program to see if gbm_bo_import works anyway.

$ cc $(pkg-config gbm --cflags --libs) gbm_test.c && ./a.out
Stat #1: mode=1880
sync #1 test failed: 9, Bad file descriptor
Lseek: length=524288
fcntl() failure: 9, Bad file descriptor
Stat #2: mode=0
sync #2 test failed: 9, Bad file descriptor
Stat #3: mode=1880
sync #3 test failed: 9, Bad file descriptor
Success!

Also, what happens if you run the drm-v5.0 branch?

Same error.

Curiously, F_GETFL fails with ENOENT before DMA_BUF_IOCTL_SYNC and EBADF after.

It's probably best to continue this at mstoeckl/waypipe#9 (comment 187149) .