While working on podman and buildah, I have noticed many messages logged on the console that look like this:

len 4 vecnum: 126 sizeof (zfs_cmd_t) 4528

After debugging this a little today, I discovered that this happens when something tries to set non-blocking i/o on a /dev/zfs filedescriptor which translates to a FIONBIO ioctl.

The zfs storage layer in for buildah and podman tries to detect whether zfs is available by opening /dev/zfs. The golang runtime libraries unconditionally try to set the descriptor into non-blocking mode causing the error message.

I can probably work around this in userland but it seems to me that the freebsd ZFS port should not print this message to console but instead return a suitable error. Currently it returns EINVAL after the printf which seems reasonable.