LanManFS patch

I started using LanManFS instead of LanMan98 recently, to access SMB shares on a Linux Suse 42.2 PC. Server is running smbd 4.4.2-11.15.1.

It seems that recently (2014!) the samba maintainers made a change to smbd for compatibility with Windows 2000. The commit to their code is here: https://git.samba.org/?p=samba.git;a=commitdiff;h=8b746f5a2137b74e28bce5370f5aa9d4bcdac6c2

This breaks LanManFS, when fetching files whose size is between 4304 and 4356 bytes.

LanManFS request a block of data of (say) 4320 bytes, and smbd truncates that to max_send - (smb_size + 5*2 + 3) where max_send is the max block size that LanManFS specified when connecting to the server, and is fixed at 4356 bytes.

The solution would seem to be to restrict LanManFS to requesting a maximum block size that matches what the server will send out. Below is the diff of my changes to LanManFS.c.SMB.

Having looked at the server code, I don’t think this problem will affect ‘raw reads’, so I didn’t modify that part of LanManFS.

Ticket here: https://www.riscosopen.org/tracker/tickets/459

--- ADFS::Rik2.$.riscos.src-iyo-dev/5/27/tar.TungstenDev.apache.RiscOS.Sources.Networking.Omni.Protocols.LanManFS.c.SMB	2018-11-16 12:03:49.0 +0000
+++ ADFS::Rik2.$.riscos.apache.RiscOS.Sources.Networking.Omni.Protocols.LanManFS.c.SMB	2018-11-16 12:03:49.0 +0000
@@ -111,6 +111,12 @@
 #define WRRAW_BLOCK_SIZE  16384
 #define PRN_BLOCK_SIZE    1024
 
+/*
+ * SMB packet size as defined in smbd/reply.c
+*/
+#define SMB_SIZE        39
+#define MAX_RX_DATA_SIZE        (MAX_RX_BLOCK_SIZE - (SMB_SIZE + 5*2 + 3))
+
 /* This structure relies on Norcroft C packing the bytes & words
    properly!
  */
@@ -2619,7 +2625,7 @@ err_t SMB_Read ( int FH, uint offset, ui
   while ( len_left > 0 )
   {
     SMB_TxWords[0] = fid;
-    SMB_TxWords[1] = min(len_left, MAX_RX_BLOCK_SIZE);
+    SMB_TxWords[1] = min(len_left, MAX_RX_DATA_SIZE);   // was MAX_RX_BLOCK_SIZE
     SMB_TxWords[2] = offset & 0xFFFF;
     SMB_TxWords[3] = (offset >> 16 );
     SMB_TxWords[4] = (len_left);
@@ -2648,7 +2654,7 @@ err_t SMB_Read ( int FH, uint offset, ui
 
     FreeChain(pB_res);
 
-    if ( n_read < MAX_RX_BLOCK_SIZE )  /* Reached end of file */
+    if ( n_read < MAX_RX_DATA_SIZE )  /* Reached end of file */ // was MAX_RX_BLOCK_SIZE
       break;
   }
 

Ignore this for now, it seems my changes have broken something else.

I’ve done some further testing and I’ve got no idea why I initially got bad results. Perhaps a compiler/linker problem, but after a clean and recompile everything seems ok with this patch.