[PATCH v2] Always report a writeback error once

The errseq_t infrastructure assumes that errors which occurred before the file descriptor was opened are of no interest to the application. This turns out to be a regression for some applications, notably Postgres. Before errseq_t, a writeback error would be reported exactly once (as long as the

[PATCH v2] Always report a writeback error once

The errseq_t infrastructure assumes that errors which occurred before the file descriptor was opened are of no interest to the application. This turns out to be a regression for some applications, notably Postgres. Before errseq_t, a writeback error would be reported exactly once (as long as the