0ab19d08a4
In r286570 (MFV of r277426) an unprotected write to b_flags to set the compression mode was introduced. This would open a race window where data is partially decompressed, modified, checksummed and written to the pool, resulting in pool corruption due to the partial decompression. Prevent this by reintroducing b_compress illumos/illumos-gate@d4cd038c92 Illumos issues: 6214 zpools going south https://www.illumos.org/issues/6214