Buffer UDF sector reads — eliminates scan hang on USB drives

src/disc/bluray.rs

@@ -12,8 +12,19 @@ impl Disc {
         reader: &mut dyn SectorReader,
         udf_fs: &udf::UdfFs,
     ) -> Vec<DiscTitle> {
+        let t0 = std::time::Instant::now();
         let mut titles = Vec::new();
         if let Some(playlist_dir) = udf_fs.find_dir("/BDMV/PLAYLIST") {
+            let mpls_count = playlist_dir
+                .entries
+                .iter()
+                .filter(|e| !e.is_dir && e.name.to_lowercase().ends_with(".mpls"))
+                .count();
+            eprintln!(
+                "[titles {:.1}s] {} MPLS files",
+                t0.elapsed().as_secs_f64(),
+                mpls_count
+            );
             for entry in &playlist_dir.entries {
                 if !entry.is_dir && entry.name.to_lowercase().ends_with(".mpls") {
                     let path = format!("/BDMV/PLAYLIST/{}", entry.name);
@@ -21,12 +32,23 @@ impl Disc {
                         if let Some(title) =
                             Self::parse_playlist(reader, udf_fs, &entry.name, &mpls_data)
                         {
+                            eprintln!(
+                                "[titles {:.1}s] {} -> title ({:.0}s)",
+                                t0.elapsed().as_secs_f64(),
+                                entry.name,
+                                title.duration_secs
+                            );
                             titles.push(title);
                         }
                     }
                 }
             }
         }
+        eprintln!(
+            "[titles {:.1}s] done: {} titles",
+            t0.elapsed().as_secs_f64(),
+            titles.len()
+        );
         titles
     }
 

src/disc/mod.rs

@@ -940,17 +940,37 @@ impl Disc {
     /// The session must be open and unlocked (Drive::open handles this).
     /// All disc reads use standard READ(10) via UDF -- no vendor SCSI commands.
     pub fn scan(session: &mut Drive, opts: &ScanOptions) -> Result<Self> {
+        let t0 = std::time::Instant::now();
         // READ CAPACITY may fail in LibreDrive mode — proceed with 0 and estimate later
         let capacity = Self::read_capacity(session).unwrap_or(0);
+        eprintln!(
+            "[scan {:.1}s] capacity={}",
+            t0.elapsed().as_secs_f64(),
+            capacity
+        );
 
         // AACS handshake (Blu-ray/UHD)
         let handshake = Self::do_handshake(session, opts);
+        eprintln!("[scan {:.1}s] handshake done", t0.elapsed().as_secs_f64());
 
         // Request max read speed — removes riplock on DVD
         // (BD/UHD speed is set by firmware init, but DVD needs explicit SET CD SPEED)
         session.set_speed(0xFFFF);
+        eprintln!("[scan {:.1}s] speed set", t0.elapsed().as_secs_f64());
 
-        let mut disc = Self::scan_with(session, capacity, handshake, opts)?;
+        let batch = detect_max_batch_sectors(session.device_path());
+        let mut buffered = udf::BufferedSectorReader::new(session, batch);
+        let udf_fs = udf::read_filesystem(&mut buffered)?;
+        eprintln!(
+            "[scan {:.1}s] UDF parsed, prefetching metadata ({} sectors)...",
+            t0.elapsed().as_secs_f64(),
+            udf_fs.metadata_sectors()
+        );
+        buffered.prefetch(udf_fs.metadata_start(), udf_fs.metadata_sectors());
+        eprintln!("[scan {:.1}s] metadata cached", t0.elapsed().as_secs_f64());
+
+        let mut disc = Self::scan_with(&mut buffered, capacity, handshake, opts, udf_fs)?;
+        eprintln!("[scan {:.1}s] scan_with done", t0.elapsed().as_secs_f64());
 
         // CSS key extraction for DVDs (bus auth → disc key → title key).
         // Must be a single auth session — can't call authenticate() separately.
@@ -988,7 +1008,8 @@ impl Disc {
         capacity: u32,
         opts: &ScanOptions,
     ) -> Result<Self> {
-        Self::scan_with(reader, capacity, None, opts)
+        let udf_fs = udf::read_filesystem(reader)?;
+        Self::scan_with(reader, capacity, None, opts, udf_fs)
     }
 
     /// Core scan pipeline — works with any SectorReader.
@@ -997,15 +1018,19 @@ impl Disc {
         capacity: u32,
         handshake: Option<HandshakeResult>,
         opts: &ScanOptions,
+        udf_fs: udf::UdfFs,
     ) -> Result<Self> {
-        // 1. UDF filesystem
+        let t0 = std::time::Instant::now();
-        let udf_fs = udf::read_filesystem(reader)?;
 
         // 2. Resolve encryption (AACS, CSS, or none)
         let encrypted =
             udf_fs.find_dir("/AACS").is_some() || udf_fs.find_dir("/BDMV/AACS").is_some();
 
         let aacs = if encrypted {
+            eprintln!(
+                "[scan_with {:.1}s] resolving encryption...",
+                t0.elapsed().as_secs_f64()
+            );
             if let Some(keydb_path) = opts.resolve_keydb() {
                 Self::resolve_encryption(&udf_fs, reader, &keydb_path, handshake.as_ref()).ok()
             } else {
@@ -1014,6 +1039,10 @@ impl Disc {
         } else {
             None
         };
+        eprintln!(
+            "[scan_with {:.1}s] encryption done",
+            t0.elapsed().as_secs_f64()
+        );
 
         // 3. Titles — BD (MPLS playlists) or DVD (IFO title sets)
         let (mut titles, content_format) = if udf_fs.find_dir("/BDMV").is_some() {
@@ -1029,6 +1058,11 @@ impl Disc {
         } else {
             (Vec::new(), ContentFormat::BdTs)
         };
+        eprintln!(
+            "[scan_with {:.1}s] titles done: {}",
+            t0.elapsed().as_secs_f64(),
+            titles.len()
+        );
         titles.sort_by(|a, b| {
             b.duration_secs
                 .partial_cmp(&a.duration_secs)
@@ -1037,7 +1071,12 @@ impl Disc {
 
         // 4. Metadata + labels
         let meta_title = Self::read_meta_title(reader, &udf_fs);
+        eprintln!(
+            "[scan_with {:.1}s] meta_title done",
+            t0.elapsed().as_secs_f64()
+        );
         crate::labels::apply(reader, &udf_fs, &mut titles);
+        eprintln!("[scan_with {:.1}s] labels done", t0.elapsed().as_secs_f64());
 
         // 5. Derive format, layers, region
         let format = Self::detect_format(&titles);

src/udf.rs

@@ -61,6 +61,11 @@ impl UdfFs {
         self.metadata_start
     }
 
+    /// Metadata partition size in sectors.
+    pub(crate) fn metadata_sectors(&self) -> u32 {
+        self.metadata_sectors
+    }
+
     /// Find a directory by path (e.g. "/BDMV/PLAYLIST").
     /// Path matching is case-insensitive.
     pub fn find_dir(&self, path: &str) -> Option<&DirEntry> {
@@ -832,6 +837,96 @@ fn parse_dstring(data: &[u8]) -> String {
 
 /// Read a single 2048-byte sector from the drive.
 /// Uses standard READ(10) — no unlock required.
+/// Buffered sector reader — reduces SCSI round-trips by pre-fetching blocks.
+/// Each SCSI command has ~500ms overhead on USB drives, so reading 32 sectors
+/// at once (one command) is 32x faster than 32 individual reads.
+pub(crate) struct BufferedSectorReader<'a> {
+    inner: &'a mut dyn SectorReader,
+    cache_start: u32,
+    cache: Vec<u8>,
+    cache_sectors: u32,
+    batch: u16,
+}
+
+impl<'a> BufferedSectorReader<'a> {
+    pub(crate) fn new(inner: &'a mut dyn SectorReader, batch: u16) -> Self {
+        Self {
+            inner,
+            cache_start: u32::MAX,
+            cache: Vec::new(),
+            cache_sectors: 0,
+            batch,
+        }
+    }
+}
+
+impl BufferedSectorReader<'_> {
+    /// Pre-read a range of sectors into the cache.
+    /// Used to bulk-load the UDF metadata partition so subsequent reads are instant.
+    pub(crate) fn prefetch(&mut self, start_lba: u32, count: u32) {
+        // Read in chunks of 30 sectors (within USB SCSI limits)
+        let total = count as usize * 2048;
+        self.cache.resize(total, 0);
+        let mut offset = 0u32;
+        while offset < count {
+            let batch = (count - offset).min(self.batch as u32) as u16;
+            let buf_off = offset as usize * 2048;
+            if self
+                .inner
+                .read_sectors(
+                    start_lba + offset,
+                    batch,
+                    &mut self.cache[buf_off..buf_off + batch as usize * 2048],
+                )
+                .is_err()
+            {
+                break;
+            }
+            offset += batch as u32;
+        }
+        self.cache_start = start_lba;
+        self.cache_sectors = offset;
+    }
+}
+
+impl SectorReader for BufferedSectorReader<'_> {
+    fn read_sectors(
+        &mut self,
+        lba: u32,
+        count: u16,
+        buf: &mut [u8],
+    ) -> std::result::Result<usize, crate::error::Error> {
+        if count == 1 {
+            // Single sector — use cache
+            if lba >= self.cache_start && lba < self.cache_start + self.cache_sectors {
+                let offset = (lba - self.cache_start) as usize * 2048;
+                buf[..2048].copy_from_slice(&self.cache[offset..offset + 2048]);
+                return Ok(2048);
+            }
+            let block = self.batch;
+            self.cache.resize(block as usize * 2048, 0);
+            match self.inner.read_sectors(lba, block, &mut self.cache) {
+                Ok(_) => {
+                    self.cache_start = lba;
+                    self.cache_sectors = block as u32;
+                }
+                Err(_) => {
+                    // Near end of disc or error — single sector fallback
+                    self.cache.resize(2048, 0);
+                    self.inner.read_sectors(lba, 1, &mut self.cache)?;
+                    self.cache_start = lba;
+                    self.cache_sectors = 1;
+                }
+            }
+            buf[..2048].copy_from_slice(&self.cache[..2048]);
+            Ok(2048)
+        } else {
+            // Multi-sector read — pass through
+            self.inner.read_sectors(lba, count, buf)
+        }
+    }
+}
+
 fn read_sector(reader: &mut dyn SectorReader, lba: u32, buf: &mut [u8]) -> Result<()> {
     reader.read_sectors(lba, 1, buf)?;
     Ok(())