mmap fails for DRM_IOCTL_MODE_MAP_DUMB for Radeon, Nouveau, and VMWGFX

[Rian Quinn]

When working with dumb buffers, DRM_IOCTL_MODE_MAP_DUMB and mmap works fine
on Intel, but the mmap call fails on Radeon, Nouveau, and VMWGFX. I you
look at the source for the xorg moderating driver, it only uses the dumb
buffer IOCTL (i.e. it’s not using LibKMS), and if you look at the kernel
source code for the dumb buffer IOCTLs for each of the Radeon, Nouveau, and
VMWGFX drivers, they all implement the functions. Furthermore all of the
IOCTLs succeed without error. Its only when you attempt to map the memory,
that you get an error of “Invalid Argument”. Here is my map call:

mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, map_arg.offset)

Is this a bug, or is there a different way to map the dumb buffers for
these drivers other than LibKMS.

Thanks,
- Rian
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