[UDFS] Implement faster free space search via roving pointer and allocation optimisations

drivers/filesystems/udfs/struct.h

@@ -684,6 +684,8 @@ struct VCB {
 
     PCHAR           FSBM_OldBitmap;  // 0 - free, 1 - used
     ULONG           BitmapModified;
+    ULONG           BitmapSearchHint; // LBA hint for next free space search (roving pointer)
+
     PCHAR           BSBM_Bitmap;     // 0 - normal, 1 - bad-block
 
     // pointers to Volume Descriptor Sequences

drivers/filesystems/udfs/udf_info/alloc.cpp

@@ -725,6 +725,7 @@ UDFAllocFreeExtent_(
     EXTENT_AD Ext;
     PEXTENT_MAP Map = NULL;
     uint32 len, LBS, BSh, blen;
+    uint32 EffectiveSearchStart;
 
     LBS = Vcb->SectorSize;
     BSh = Vcb->SectorShift;
@@ -740,11 +741,31 @@ UDFAllocFreeExtent_(
     if (blen > (SearchLim - SearchStart)) {
         goto no_free_space_err;
     }
+
+    // Use the bitmap search hint for allocation locality: start near the last
+    // allocation to avoid scanning already-used space at the start of the partition.
+    // The hint is only valid when it falls within [SearchStart, SearchLim); any
+    // out-of-range value is silently ignored and the full range is scanned instead.
+    EffectiveSearchStart = SearchStart;
+    if (Vcb->BitmapSearchHint >= SearchStart && Vcb->BitmapSearchHint < SearchLim) {
+        EffectiveSearchStart = Vcb->BitmapSearchHint;
+        AdPrint(("  BitmapSearchHint applied: hint @%x, effective start @%x\n",
+            Vcb->BitmapSearchHint, EffectiveSearchStart));
+    }
+
     // walk through the free space bitmap & find a single extent or a set of
     // frags giving in sum the Length specified
     while(blen) {
-        Ext.extLocation = UDFFindMinSuitableExtent(Vcb, blen, SearchStart,
-                                                               SearchLim, &len, AllocFlags);
+        Ext.extLocation = UDFFindMinSuitableExtent(Vcb, blen, EffectiveSearchStart,
+                                                   SearchLim, &len, AllocFlags);
+        if (!len && EffectiveSearchStart > SearchStart) {
+            // Nothing found from the hint onward; fall back to a full-range search
+            AdPrint(("  BitmapSearchHint: no free space from @%x, falling back to full scan from @%x\n",
+                EffectiveSearchStart, SearchStart));
+            EffectiveSearchStart = SearchStart;
+            Ext.extLocation = UDFFindMinSuitableExtent(Vcb, blen, SearchStart,
+                                                       SearchLim, &len, AllocFlags);
+        }
 
         if (len >= blen) {
             // complete search
@@ -777,12 +798,16 @@ UDFAllocFreeExtent_(
                 AdPrint(("newly allocated extent contains BB\n"));
                 UDFMarkSpaceAsXXXNoProtect(Vcb, 0, ExtInfo->Mapping, AS_DISCARDED); // free
                 UDFMarkBadSpaceAsUsed(Vcb, Ext.extLocation, Ext.extLength >> BSh); // bad -> bad+used
-                // roll back
+                // Advance past the bad blocks and roll back the length
+                EffectiveSearchStart = Ext.extLocation + (Ext.extLength >> BSh);
                 blen += Ext.extLength>>BSh;
                 continue;
             }
         }
 
+        // Advance the search position past the just-allocated extent
+        EffectiveSearchStart = Ext.extLocation + (Ext.extLength >> BSh);
+
         Ext.extLength |= EXTENT_NOT_RECORDED_ALLOCATED << 30;
         if (!(ExtInfo->Mapping)) {
             // create new
@@ -818,6 +843,10 @@ UDFAllocFreeExtent_(
             return STATUS_INSUFFICIENT_RESOURCES;
         }
     }
+    // Persist the search position for future allocations (success path only;
+    // failure paths all return before reaching here via no_free_space_err).
+    AdPrint(("  BitmapSearchHint updated: @%x -> @%x\n", Vcb->BitmapSearchHint, EffectiveSearchStart));
+    Vcb->BitmapSearchHint = EffectiveSearchStart;
     UDFReleaseResource(&(Vcb->BitMapResource1));
     ExtInfo->Length = Length;
     return STATUS_SUCCESS;

drivers/filesystems/udfs/udf_info/extent.cpp

@@ -1492,7 +1492,9 @@ UDFFlushAllCachedAllocations(
 
 /*
     This routine allocates space for FE of the file being created.
-    Allocates a single block from the partition bitmap.
+    The BitmapSearchHint roving pointer inside UDFAllocFreeExtent_ automatically
+    starts the scan near the last successful allocation, providing locality
+    without a separate window-probe mechanism.
  */
 NTSTATUS
 UDFAllocateFESpace(
@@ -1505,8 +1507,12 @@ UDFAllocateFESpace(
     )
 {
     UNREFERENCED_PARAMETER(DirInfo);
+    uint32 p_start = UDFPartStart(Vcb, PartNum);
+    uint32 p_end   = UDFPartEnd(Vcb, PartNum);
+    AdPrint(("UDFAllocateFESpace: Part %x, [%x..%x], Len %x\n",
+        PartNum, p_start, p_end, Len));
     return UDFAllocFreeExtent(IrpContext, Vcb, Len,
-           UDFPartStart(Vcb, PartNum), UDFPartEnd(Vcb, PartNum), FEExtInfo, EXTENT_FLAG_VERIFY);
+           p_start, p_end, FEExtInfo, EXTENT_FLAG_VERIFY);
 } // end UDFAllocateFESpace()
 
 /*
@@ -2228,6 +2234,9 @@ UDFResizeExtent(
                    (ExtInfo->Flags & EXTENT_FLAG_ALLOC_MASK) == EXTENT_FLAG_ALLOC_SEQUENTIAL) {
                     AdPrint(("Resize tune for SEQUENTIAL i/o\n"));
                 }
+                // BitmapSearchHint inside UDFAllocFreeExtent_ provides locality
+                // automatically by starting the scan near the last successful
+                // allocation, so a full-partition call is all that is needed.
                 status = UDFAllocFreeExtent(IrpContext, Vcb, Length - l,
                                                    UDFPartStart(Vcb, PartNum),
                                                    UDFPartEnd(Vcb, PartNum),

drivers/filesystems/udfs/udf_info/udf_info.cpp

@@ -43,6 +43,13 @@ static const char valid_char_arr[] = {"*/:?\"<>|\\"};
 
 #define DOS_CRC_MODULUS 41
 #define hexChar crcChar
+
+// Minimum number of sectors to pre-allocate for a new directory data extent.
+// Amortises per-sector cold-write spikes across many file additions.
+// The effective pre-allocation is max(2*t, UDF_DIR_PREALLOC_MIN_SECTORS *
+// SectorSize) rounded up to a WriteBlockSize boundary.
+#define UDF_DIR_PREALLOC_MIN_SECTORS  8
+
 static const char crcChar[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ#_~-@";
 
 /* Used to convert hex digits to ASCII for readability. */
@@ -1623,8 +1630,16 @@ UDFWriteFile__(
         WasInIcb ? "In-Icb" : "",
         Vcb->LowFreeSpace ? "LowSpace" : ""));
     if (UDFIsADirectory(FileInfo) && !WasInIcb && !Vcb->LowFreeSpace) {
+        // Pre-allocate directory data extents in larger chunks to amortise
+        // per-sector cold-write spikes across many file additions.
+        // The pre-allocation size is at least UDF_DIR_PREALLOC_MIN_SECTORS
+        // sectors (safety net for small WriteBlockSize configurations) and
+        // is always rounded up to a full WriteBlockSize boundary.
+        uint64 prealloc = max((uint64)t * 2,
+                              (uint64)Vcb->SectorSize * UDF_DIR_PREALLOC_MIN_SECTORS);
+        prealloc = (prealloc + Vcb->WriteBlockSize - 1) & ~(ULONGLONG)(Vcb->WriteBlockSize - 1);
         FileInfo->Dloc->DataLoc.Flags |= EXTENT_FLAG_ALLOC_SEQUENTIAL;
-        status = UDFResizeExtent(IrpContext, Vcb, PartNum, (t*2+Vcb->WriteBlockSize-1) & ~(ULONGLONG)(Vcb->WriteBlockSize-1), FALSE, &(Dloc->DataLoc));
+        status = UDFResizeExtent(IrpContext, Vcb, PartNum, prealloc, FALSE, &(Dloc->DataLoc));
         if (NT_SUCCESS(status)) {
             AdPrint(("  preallocated space for Dir\n"));
             FileInfo->Dloc->DataLoc.Flags |= EXTENT_FLAG_PREALLOCATED;
@@ -3000,8 +3015,15 @@ UDFCreateFile__(
         FileInfo->Dloc->DataLoc.Mapping[0].extLength &= UDF_EXTENT_LENGTH_MASK;
         FileInfo->Dloc->DataLoc.Modified = TRUE;
         FileInfo->Dloc->FELoc.Mapping[0].extLength &= UDF_EXTENT_LENGTH_MASK;
-        // zero sector for FileEntry
+        // Mark the FE sector as newly allocated so that UDFFlushFE writes the
+        // full sector (FE content + zero padding) in a single call instead of
+        // the previous two-step sequence (explicit zero-write here followed by
+        // a read-modify-write inside UDFWriteInSector).  CDR media still needs
+        // the explicit zero-write because UDFFlushFE skips the padded path in
+        // that mode.
         if (!Vcb->CDR_Mode) {
+            FileInfo->Dloc->FE_Flags |= UDF_FE_FLAG_NEW_SECTOR;
+        } else {
             status = UDFWriteData(IrpContext, Vcb, TRUE, ((int64)(FileInfo->Dloc->FELoc.Mapping[0].extLocation)) << Vcb->SectorShift, LBS, FALSE, Vcb->ZBuffer, &WrittenBytes);
             if (!NT_SUCCESS(status)) {
                 UDFFlushFI(IrpContext, Vcb, FileInfo, PartNum);
@@ -3637,7 +3659,15 @@ UDFRecordDirectory__(
     if (!NT_SUCCESS(status)) return status;
     if (CurDirNdx) CurDirNdx->FileCharacteristics =
         DirInfo->FileIdent->fileCharacteristics;
-    return UDFIndexDirectory(IrpContext, Vcb, DirInfo);
+    status = UDFIndexDirectory(IrpContext, Vcb, DirInfo);
+    if (!NT_SUCCESS(status)) return status;
+    // The FE was already written by UDFCreateFile__'s UDFFlushFE as a regular
+    // empty file.  UDFWriteFile__ above modified DataLoc (new allocation,
+    // non-zero informationLength) and the in-memory FE now has
+    // fileType = UDF_FILE_TYPE_DIRECTORY.  Flush the FE now so that the
+    // on-disk copy is consistent; without this a crash before close would
+    // leave a corrupt regular-empty-file FE on disk.
+    return UDFFlushFE(IrpContext, Vcb, DirInfo, PartNum);
 } // end UDFRecordDirectory__()
 
 /*
@@ -4180,10 +4210,46 @@ UDFFlushFE(
                     UDFPhysLbaToPart(Vcb, PartNum, lba), 0);
             }
         }
-        status = UDFWriteExtent(
-            IrpContext,
-            Vcb, &FileInfo->Dloc->FELoc, 0, (uint32)(FileInfo->Dloc->FELoc.Length), FALSE,
-            (int8 *)(FileInfo->Dloc->FileEntry), &WrittenBytes);
+        // Write the FE to disk.  When the FE sector was freshly allocated in
+        // this file-creation call (UDF_FE_FLAG_NEW_SECTOR is set), write the
+        // full sector as a single zero-padded buffer.  This replaces the
+        // previous three-step sequence (zero-write the sector in
+        // UDFCreateFile__, then read-before-write inside UDFWriteInSector when
+        // the FE is smaller than a full sector) with a single write I/O.
+        {
+            BOOLEAN newSector = !!(FileInfo->Dloc->FE_Flags & UDF_FE_FLAG_NEW_SECTOR);
+            uint32 feLen = (uint32)(FileInfo->Dloc->FELoc.Length);
+            uint32 LBS_fe = Vcb->SectorSize;
+            FileInfo->Dloc->FE_Flags &= ~UDF_FE_FLAG_NEW_SECTOR;
+
+            if (newSector && feLen < LBS_fe) {
+                // Allocate a sector-sized staging buffer, copy the FE into the
+                // beginning, and zero-fill the rest so the trailing bytes are
+                // clean without a separate read-modify-write.
+                int8* padBuf = (int8*)MyAllocatePool__(NonPagedPool, LBS_fe);
+                if (padBuf) {
+                    RtlCopyMemory(padBuf, FileInfo->Dloc->FileEntry, feLen);
+                    RtlZeroMemory(padBuf + feLen, LBS_fe - feLen);
+                    SIZE_T _wb = 0;
+                    status = UDFWriteData(IrpContext, Vcb, TRUE,
+                        ((int64)lba) << Vcb->SectorShift, LBS_fe, FALSE, padBuf, &_wb);
+                    WrittenBytes = _wb;
+                    MyFreePool__(padBuf);
+                } else {
+                    // Pool exhausted; fall through to the regular path which
+                    // may do a read-modify-write but is always correct.
+                    status = UDFWriteExtent(
+                        IrpContext,
+                        Vcb, &FileInfo->Dloc->FELoc, 0, feLen, FALSE,
+                        (int8 *)(FileInfo->Dloc->FileEntry), &WrittenBytes);
+                }
+            } else {
+                status = UDFWriteExtent(
+                    IrpContext,
+                    Vcb, &FileInfo->Dloc->FELoc, 0, feLen, FALSE,
+                    (int8 *)(FileInfo->Dloc->FileEntry), &WrittenBytes);
+            }
+        }
         if (!NT_SUCCESS(status)) {
             UDFPrint(("  FlushFE: UDFWriteExtent(2) failed (%x)\n", status));
             if (status == STATUS_DEVICE_DATA_ERROR) {

drivers/filesystems/udfs/udf_info/udf_rel.h

@@ -325,6 +325,10 @@ typedef struct _UDF_DATALOC_INFO {
 #define UDF_FE_FLAG_IS_DEL_SDIR  (0x20)
 /// Dloc is being initialized, don't touch it now
 #define UDF_FE_FLAG_UNDER_INIT   (0x40)
+/// FE sector is freshly allocated; UDFFlushFE must write it zero-padded
+/// to the full sector size to avoid a separate zero-init write followed by
+/// a read-modify-write.  Cleared by UDFFlushFE after the padded write.
+#define UDF_FE_FLAG_NEW_SECTOR   (0x80)
 
 
 #define UDF_FILE_INFO_MT PagedPool