Built it as a module, loaded it in an ESXi 6.0 VM with the PV SCSI controller and ran fsx for a while.
```
# kldload vmw_pvscsi
pvscsi0: <VMware para-virtual SCSI driver v1.1.2.0> port 0x4000-0x4007 mem 0xfd4f8000-0xfd4fffff irq 18 at device 0.0 on pci3
pvscsi0: Maximum number of targets is 16
pvscsi0: retval>6, msix_vecs_needed>1
pvscsi0: Using INTx interrupts
pvscsi0: softc:0xfffff80003b31400, unmasking interrupts w/intr-status 0
da0 at pvscsi0 bus 0 scbus2 target 0 lun 0
da0: <VMware Virtual disk 1.0> Fixed Direct Access SCSI-2 device
da0: 4294967.295MB/s transfers
da0: 8192MB (16777216 512 byte sectors)
da0: quirks=0x40<RETRY_BUSY>
# gpart create -s GPT da0
(da0:pvscsi0:0:0:0): WRITE(6). CDB: 0a 00 00 00 01 00
(da0:pvscsi0:0:0:0): CAM status: SCSI Status Error
(da0:pvscsi0:0:0:0): SCSI status: Busy
(da0:pvscsi0:0:0:0): Retrying command
da0 created
# gpart add -t freebsd-ufs da0
da0p1 added
# newfs /dev/da0p1
/dev/da0p1: 8192.0MB (16777136 sectors) block size 32768, fragment size 4096
using 14 cylinder groups of 626.09MB, 20035 blks, 80256 inodes.
super-block backups (for fsck_ffs -b #) at:
192, 1282432, 2564672, 3846912, 5129152, 6411392, 7693632, 8975872, 10258112,
11540352, 12822592, 14104832, 15387072, 16669312
# mount /dev/da0p1 /mnt
# /fsx /mnt/foo
truncating to largest ever: 0x13e76
truncating to largest ever: 0x2e52c
truncating to largest ever: 0x3c2c2
truncating to largest ever: 0x3f15f
truncating to largest ever: 0x3fcb9
truncating to largest ever: 0x3fe96
truncating to largest ever: 0x3ff9d
truncating to largest ever: 0x3ffff
```