+ assert(off <= r->sz); assert(want <= r->sz - off);
+ n = read_sectors(pos, r->buf + off*SECTORSZ, want);
+ return (n);
+}
+
+static ssize_t recovery_read(struct recoverybuf *r,
+ secaddr pos, secaddr want)
+{
+ secaddr diff, pp, nn;
+ ssize_t n;
+
+#ifdef DEBUG
+ debug_clear_progress();
+ show_recovery_buffer_map(r, "begin(%"PRIuSEC", %"PRIuSEC")", pos, want);
+#endif
+
+ if (pos < r->pos) {
+ diff = r->pos - pos;
+ if (r->start + diff >= r->sz) {
+ r->pos = pos; r->start = r->end = 0;
+#ifdef DEBUG
+ show_recovery_buffer_map(r, "cleared; shift up by %"PRIuSEC"", diff);
+#endif
+ } else {
+ if (r->end + diff > r->sz) r->end = r->sz - diff;
+ rearrange_sectors(r, r->start + diff, r->start, r->end - r->start);
+ r->pos -= diff; r->start += diff; r->end += diff;
+#ifdef DEBUG
+ show_recovery_buffer_map(r, "shifted up by %"PRIuSEC"", diff);
+#endif
+ }
+ } else if (pos > r->pos + r->end) {
+ r->pos = pos; r->start = r->end = 0;
+#ifdef DEBUG
+ show_recovery_buffer_map(r, "cleared; beyond previous region");
+#endif
+ } else if (pos + want > r->pos + r->sz) {
+ diff = (pos + want) - (r->pos + r->sz);
+ if (r->end <= diff) {
+ r->pos = pos; r->start = r->end = 0;
+#ifdef DEBUG
+ show_recovery_buffer_map(r, "cleared; shift down by %"PRIuSEC"", diff);
+#endif
+ } else {
+ if (r->start < diff) r->start = diff;
+ rearrange_sectors(r, r->start - diff, r->start, r->end - r->start);
+ r->pos += diff; r->start -= diff; r->end -= diff;
+#ifdef DEBUG
+ show_recovery_buffer_map(r, "shifted down by %"PRIuSEC"", diff);
+#endif
+ }
+ }
+
+ if (pos < r->pos + r->start) {
+ pp = pos - r->pos; nn = r->start - pp;
+#ifdef DEBUG
+ printf(";; read low (%"PRIuSEC"@%"PRIuSEC", %"PRIuSEC")", pos, pp, nn);
+ fflush(stdout);
+#endif
+ n = recovery_read_sectors(r, pos, pp, nn);
+#ifdef DEBUG
+ printf(" -> %zd\n", n);
+#endif
+ if (n != nn) {
+ if (n >= 0 && n > want) n = want;
+ goto end;
+ }
+ r->start = pp;
+#ifdef DEBUG
+ show_recovery_buffer_map(r, "joined new region");
+#endif
+ }
+
+ if (pos + want > r->pos + r->end) {
+ pp = r->end; nn = (pos + want) - (r->pos + r->end);
+#ifdef DEBUG
+ printf(";; read high (%"PRIuSEC"@%"PRIuSEC", %"PRIuSEC")",
+ r->pos + pp, pp, nn);
+ fflush(stdout);
+#endif
+ n = recovery_read_sectors(r, r->pos + pp, pp, nn);
+#ifdef DEBUG
+ printf(" -> %zd\n", n);
+#endif
+ if (n > 0) {
+ r->end += n;
+#ifdef DEBUG
+ show_recovery_buffer_map(r, "joined new region");
+#endif
+ }
+ }
+
+ n = r->pos + r->end - pos;
+ if (!n && want) n = -1;
+
+end:
+#ifdef DEBUG
+ show_recovery_buffer_map(r, "done; return %zd", n);
+#endif
+ return (n);
+}
+
+static secaddr run_length_wanted(secaddr pos, secaddr badlen,
+ secaddr sz, secaddr end)
+{
+ secaddr want;
+
+ want = 3*badlen/2;
+ if (!want) want = 1;
+ if (want > end - pos) want = end - pos;
+ if (want > sz) want = sz;
+ return (want);
+}
+
+static ssize_t find_good_sector(secaddr *pos_inout, secaddr end,
+ unsigned char *buf, secaddr sz)
+{
+ int i;
+ secaddr pos = *pos_inout, bad_lo, bad_hi, good, step, want;
+ struct recoverybuf r;
+ ssize_t n;
+
+ r.buf = buf; r.sz = sz; r.pos = r.start = r.end = 0;
+ report_bad_blocks_progress(pos, pos, errno);
+
+ want = sz; if (want > end - pos) want = end - pos;
+ for (i = 0; i < 4; i++) {
+ n = recovery_read(&r, pos, want);
+#ifdef DEBUG
+ debug_clear_progress();
+ printf(";; [retry] try reading %"PRIuSEC" .. %"PRIuSEC" -> %zd\n",
+ pos, pos + want, n);
+#endif
+ if (n > 0) {
+ clear_progress();
+ moan("sector %"PRIuSEC" read ok after retry", pos);
+ return (n);
+ }