+/**
+* @name UpdateMftMirror
+* @implemented
+*
+* Backs-up the first ~4 master file table entries to the $MFTMirr file.
+*
+* @param Vcb
+* Pointer to an NTFS_VCB for the volume whose Mft mirror is being updated.
+*
+* @returninja livecd
+
+* STATUS_SUCCESS on success.
+* STATUS_INSUFFICIENT_RESOURCES if an allocation failed.
+* STATUS_UNSUCCESSFUL if we couldn't read the master file table.
+*
+* @remarks
+* NTFS maintains up-to-date copies of the first several mft entries in the $MFTMirr file. Usually, the first 4 file
+* records from the mft are stored. The exact number of entries is determined by the size of $MFTMirr's $DATA.
+* If $MFTMirr is not up-to-date, chkdsk will reject every change it can find prior to when $MFTMirr was last updated.
+* Therefore, it's recommended to call this function if the volume changes considerably. For instance, IncreaseMftSize()
+* relies on this function to keep chkdsk from deleting the mft entries it creates. Note that under most instances, creating
+* or deleting a file will not affect the first ~four mft entries, and so will not require updating the mft mirror.
+*/
+NTSTATUS
+UpdateMftMirror(PNTFS_VCB Vcb)
+{
+ PFILE_RECORD_HEADER MirrorFileRecord;
+ PNTFS_ATTR_CONTEXT MirrDataContext;
+ PNTFS_ATTR_CONTEXT MftDataContext;
+ PCHAR DataBuffer;
+ ULONGLONG DataLength;
+ NTSTATUS Status;
+ ULONG BytesRead;
+ ULONG LengthWritten;
+
+ // Allocate memory for the Mft mirror file record
+ MirrorFileRecord = ExAllocatePoolWithTag(NonPagedPool, Vcb->NtfsInfo.BytesPerFileRecord, TAG_NTFS);
+ if (!MirrorFileRecord)
+ {
+ DPRINT1("Error: Failed to allocate memory for $MFTMirr!\n");
+ return STATUS_INSUFFICIENT_RESOURCES;
+ }
+
+ // Read the Mft Mirror file record
+ Status = ReadFileRecord(Vcb, NTFS_FILE_MFTMIRR, MirrorFileRecord);
+ if (!NT_SUCCESS(Status))
+ {
+ DPRINT1("ERROR: Failed to read $MFTMirr!\n");
+ ExFreePoolWithTag(MirrorFileRecord, TAG_NTFS);
+ return Status;
+ }
+
+ // Find the $DATA attribute of $MFTMirr
+ Status = FindAttribute(Vcb, MirrorFileRecord, AttributeData, L"", 0, &MirrDataContext, NULL);
+ if (!NT_SUCCESS(Status))
+ {
+ DPRINT1("ERROR: Couldn't find $DATA attribute!\n");
+ ExFreePoolWithTag(MirrorFileRecord, TAG_NTFS);
+ return Status;
+ }
+
+ // Find the $DATA attribute of $MFT
+ Status = FindAttribute(Vcb, Vcb->MasterFileTable, AttributeData, L"", 0, &MftDataContext, NULL);
+ if (!NT_SUCCESS(Status))
+ {
+ DPRINT1("ERROR: Couldn't find $DATA attribute!\n");
+ ReleaseAttributeContext(MirrDataContext);
+ ExFreePoolWithTag(MirrorFileRecord, TAG_NTFS);
+ return Status;
+ }
+
+ // Get the size of the mirror's $DATA attribute
+ DataLength = AttributeDataLength(MirrDataContext->pRecord);
+
+ ASSERT(DataLength % Vcb->NtfsInfo.BytesPerFileRecord == 0);
+
+ // Create buffer for the mirror's $DATA attribute
+ DataBuffer = ExAllocatePoolWithTag(NonPagedPool, DataLength, TAG_NTFS);
+ if (!DataBuffer)
+ {
+ DPRINT1("Error: Couldn't allocate memory for $DATA buffer!\n");
+ ReleaseAttributeContext(MftDataContext);
+ ReleaseAttributeContext(MirrDataContext);
+ ExFreePoolWithTag(MirrorFileRecord, TAG_NTFS);
+ return STATUS_INSUFFICIENT_RESOURCES;
+ }
+
+ ASSERT(DataLength < ULONG_MAX);
+
+ // Back up the first several entries of the Mft's $DATA Attribute
+ BytesRead = ReadAttribute(Vcb, MftDataContext, 0, DataBuffer, (ULONG)DataLength);
+ if (BytesRead != (ULONG)DataLength)
+ {
+ DPRINT1("Error: Failed to read $DATA for $MFTMirr!\n");
+ ReleaseAttributeContext(MftDataContext);
+ ReleaseAttributeContext(MirrDataContext);
+ ExFreePoolWithTag(DataBuffer, TAG_NTFS);
+ ExFreePoolWithTag(MirrorFileRecord, TAG_NTFS);
+ return STATUS_UNSUCCESSFUL;
+ }
+
+ // Write the mirror's $DATA attribute
+ Status = WriteAttribute(Vcb,
+ MirrDataContext,
+ 0,
+ (PUCHAR)DataBuffer,
+ DataLength,
+ &LengthWritten,
+ MirrorFileRecord);
+ if (!NT_SUCCESS(Status))
+ {
+ DPRINT1("ERROR: Failed to write $DATA attribute of $MFTMirr!\n");
+ }
+
+ // Cleanup
+ ReleaseAttributeContext(MftDataContext);
+ ReleaseAttributeContext(MirrDataContext);
+ ExFreePoolWithTag(DataBuffer, TAG_NTFS);
+ ExFreePoolWithTag(MirrorFileRecord, TAG_NTFS);
+
+ return Status;
+}
+
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