extent scan: shorten task name for extent map

Linux kernel thread names are hardcoded at 16 characters.  Every character
counts, and "0x" wastes two.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

docs/btrfs-kernel.md

@@ -55,6 +55,7 @@ These bugs are particularly popular among bees users, though not all are specifi
 | 5.4 | 5.11 | spurious tree checker failures on extent ref hash | 5.4.125, 5.10.43, 5.11.5, 5.12 and later | 1119a72e223f btrfs: tree-checker: do not error out if extent ref hash doesn't match
 | - | 5.11 | tree mod log issue #5 | 4.4.263, 4.9.263, 4.14.227, 4.19.183, 5.4.108, 5.10.26, 5.11.9, 5.12 and later | dbcc7d57bffc btrfs: fix race when cloning extent buffer during rewind of an old root
 | - | 5.12 | tree mod log issue #6 | 4.14.233, 4.19.191, 5.4.118, 5.10.36, 5.11.20, 5.12.3, 5.13 and later | f9690f426b21 btrfs: fix race when picking most recent mod log operation for an old root
+| 5.11 | 5.12 | subvols marked for deletion with `btrfs sub del` become permanently undeletable ("ghost" subvols) | 5.12 stopped creation of new ghost subvols | Partially fixed in 8d488a8c7ba2 btrfs: fix subvolume/snapshot deletion not triggered on mount.  Qu wrote a [patch](https://github.com/adam900710/linux/commit/9de990fcc8864c376eb28aa7482c54321f94acd4) to allow `btrfs sub del -i` to remove "ghost" subvols, but it was never merged upstream.
 | 4.15 | 5.16 | spurious warnings from `fs/fs-writeback.c` when `flushoncommit` is enabled | 5.15.27, 5.16.13, 5.17 and later | a0f0cf8341e3 btrfs: get rid of warning on transaction commit when using flushoncommit
 | - | 5.17 | crash during device removal can make filesystem unmountable | 5.15.54, 5.16.20, 5.17.3, 5.18 and later | bbac58698a55 btrfs: remove device item and update super block in the same transaction
 | - | 5.18 | wrong superblock num_devices makes filesystem unmountable | 4.14.283, 4.19.247, 5.4.198, 5.10.121, 5.15.46, 5.17.14, 5.18.3, 5.19 and later | d201238ccd2f btrfs: repair super block num_devices automatically

src/bees-roots.cc

@@ -1148,7 +1148,7 @@ BeesScanModeExtent::SizeTier::find_next_extent()
 		const auto hold_state = m_crawl->hold_state(this_state);
 		const auto sft = shared_from_this();
 		ostringstream oss;
-		oss << "map_" << to_hex(this_bytenr) << "_" << pretty(this_length);
+		oss << "map_" << hex << this_bytenr << dec << "_" << pretty(this_length);
 		Task create_map_task(oss.str(), [sft, this_bytenr, hold_state, this_length, find_next_task]() {
 			sft->create_extent_map(this_bytenr, hold_state, this_length, find_next_task);
 			BEESCOUNT(crawl_extent);
@@ -1323,7 +1323,8 @@ BeesScanModeExtent::next_transid()
 		}
 		const auto bytenr_offset = min(bi_last_bytenr, max(bytenr, bi.first_bytenr)) - bi.first_bytenr + bi.first_total;
 		const auto bytenr_norm = bytenr_offset / double(fs_size);
-		const auto time_so_far = now - min(now, this_state.m_started);
+		const auto eta_start = min(now, this_state.m_started);
+		const auto time_so_far = now - eta_start;
 		const string start_stamp = strf_localtime(this_state.m_started);
 		string eta_stamp = "-";
 		string eta_pretty = "-";
@@ -1333,9 +1334,10 @@ BeesScanModeExtent::next_transid()
 			// eta_stamp = "idle";
 		} else if (time_so_far > 10 && bytenr_offset > 1024 * 1024 * 1024) {
 			const time_t eta_duration = time_so_far / bytenr_norm;
-			const time_t eta_time = eta_duration + now;
+			const time_t eta_time = eta_duration + eta_start;
+			const time_t eta_remain = eta_time - now;
 			eta_stamp = strf_localtime(eta_time);
-			eta_pretty = pretty_seconds(eta_duration);
+			eta_pretty = pretty_seconds(eta_remain);
 		}
 		const auto &mma = mes.m_map.at(subvol);
 		const auto mma_ratio = mes_sample_size_ok ? (mma.m_bytes / double(mes.m_total)) : 1.0;