We currently don't implement the /dev/full device, which is present in NetBSD, FreeBSD, and Linux.
For those who haven't heard of it, it's basically the same as /dev/zero, but writes to it always return ENOSPC. The lack of /dev/full on OpenBSD has previously caused minor issues with third party software, for example: https://bugs.python.org/issue21934 Adding support for /dev/full is trivial. I've attached a patch for amd64, if there is interest I can easily produce a set of patches for other archs. To create the device file, you'll need to do: # mknod -m 666 /dev/full c 2 5 For those who are interested, I've written a more in-depth discussion about memory special devices, including a proposal for another such new device, /dev/fill: https://research.exoticsilicon.com/articles/memory_special_devices --- arch/amd64/amd64/mem.c.dist Wed Mar 24 11:26:39 2021 +++ arch/amd64/amd64/mem.c Thu Mar 2 11:10:30 2023 @@ -88,6 +88,7 @@ break; return (EPERM); case 2: + case 5: case 12: break; #ifdef APERTURE @@ -165,9 +166,13 @@ uio->uio_resid = 0; return (0); + /* minor device 5 is /dev/full */ /* minor device 12 is /dev/zero */ + case 5: case 12: if (uio->uio_rw == UIO_WRITE) { + if (minor(dev)==5) + return (ENOSPC); c = iov->iov_len; break; }
