Make internal calls to EnsureFileSize saturate at 0xFFFFFFFF rather than error

The corresponding external interface, OS_Args 6, takes a byte size in R2 which is passed on verbatim. However, when FileSwitch wants to do the same operation it rounds up to the nearest buffer size and complains the operation can't complete ("File too big") when the same operation through OS_Args would succeed.
Internally FileSwitch doesn't actually use the allocated size for anything (other than to avoid unnecesary ensures, and to cache the value for read back via OS_Args 4), so the full byte range of R2 is now allowed internally as well as externally.
FSEntry_Open may also pass back 0xFFFFFFFF as the allocated size on opening similarly.
FSEntry_Args 7 and FSEntry_Args 4 are the corresponding low level API, these are unchanged in meaning.

The FSEntry_Args 8, write 0s to file (usually triggered by extending with EXT#handle=number), is defined as always passing the file offset as a multiple of the buffer size, and the number of 0s to write as a multiple of the buffer size. To allow this to write up to 4G of 0s while not spilling over R3, FileSwitch now splits such a call into one buffer, followed by the remainder.

Tested with LanManFS 2.38, checking operations are split appropriately.

Version 2.79. Tagged as 'FileSwitch-2_79'

VersionASM

@@ -11,13 +11,13 @@
                         GBLS    Module_HelpVersion
                         GBLS    Module_ComponentName
                         GBLS    Module_ComponentPath
-Module_MajorVersion     SETS    "2.78"
-Module_Version          SETA    278
+Module_MajorVersion     SETS    "2.79"
+Module_Version          SETA    279
 Module_MinorVersion     SETS    ""
-Module_Date             SETS    "15 Jul 2012"
-Module_ApplicationDate  SETS    "15-Jul-12"
+Module_Date             SETS    "19 Nov 2012"
+Module_ApplicationDate  SETS    "19-Nov-12"
 Module_ComponentName    SETS    "FileSwitch"
 Module_ComponentPath    SETS    "castle/RiscOS/Sources/FileSys/FileSwitch"
-Module_FullVersion      SETS    "2.78"
-Module_HelpVersion      SETS    "2.78 (15 Jul 2012)"
+Module_FullVersion      SETS    "2.79"
+Module_HelpVersion      SETS    "2.79 (19 Nov 2012)"
                         END

VersionNum

-/* (2.78)
+/* (2.79)
  *
  * This file is automatically maintained by srccommit, do not edit manually.
  * Last processed by srccommit version: 1.1.
  *
  */
-#define Module_MajorVersion_CMHG        2.78
+#define Module_MajorVersion_CMHG        2.79
 #define Module_MinorVersion_CMHG        
-#define Module_Date_CMHG                15 Jul 2012
+#define Module_Date_CMHG                19 Nov 2012
 
-#define Module_MajorVersion             "2.78"
-#define Module_Version                  278
+#define Module_MajorVersion             "2.79"
+#define Module_Version                  279
 #define Module_MinorVersion             ""
-#define Module_Date                     "15 Jul 2012"
+#define Module_Date                     "19 Nov 2012"
 
-#define Module_ApplicationDate          "15-Jul-12"
+#define Module_ApplicationDate          "19-Nov-12"
 
 #define Module_ComponentName            "FileSwitch"
 #define Module_ComponentPath            "castle/RiscOS/Sources/FileSys/FileSwitch"
 
-#define Module_FullVersion              "2.78"
-#define Module_HelpVersion              "2.78 (15 Jul 2012)"
-#define Module_LibraryVersionInfo       "2:78"
+#define Module_FullVersion              "2.79"
+#define Module_HelpVersion              "2.79 (19 Nov 2012)"
+#define Module_LibraryVersionInfo       "2:79"

s/OSGBPB

@@ -836,7 +836,7 @@ BufferedMultipleWrite EntryS "r1, bcb"
 
 ; In    fileptr = length of file to extend and fill with zeroes to
 ;       extent  = old extent of file
-;       r1      = new extent of file (endptr)
+;       r1      = new extent of file (endptr), known nonzero
 
 ; WriteMultiple needs to extend the file
 
@@ -850,7 +850,8 @@ GBPBExtendFile Entry "r0-r2, fileptr, extent"
  DREG r1, "WriteMultiple causing file extension, new endptr "
  ]
         ADD     r2, r1, bufmask         ; Round xx001 -> xx100, but not xx000
-        BIC     r2, r2, bufmask
+        BICS    r2, r2, bufmask
+        MOVEQ   r2, #&FFFFFFFF          ; Saturate at 4G-1
         BL      EnsureFileSize          ; Uses scb_extent
         EXIT    VS
 

s/StreamBits

@@ -35,7 +35,7 @@ scb_fshandle    #       4       ; Real Filing System handle  } Keep together
 scb_fscb        #       4       ; Ptr to associated fscb     }   in order
 
 scb_devid       #       4       ; Stream identifier, normally zero
-scb_allocsize   #       4       ; Size currently allocated on disc
+scb_allocsize   #       4       ; Size currently allocated on disc, buffer aligned (saturate at 4G-1)
 
 scb_special     #       4       ; Pointer to special field (SGetAreaed) or scb^ used to open this file
 scb_path        #       4       ; Pointer to path tail (SGetAreaed) used to open this file
@@ -673,10 +673,7 @@ GetFileBuffer Entry
 
 EnsureBufferValidForWrite Entry "r1-r2"
 
-        BL      FindFileBuffer          ; Got the right buffer here ?
-        EXIT    NE                      ; [yes]
-
-        BL      GetFileBuffer           ; Better run and get it
+        BL      EnsureBufferValid       ; Get bcb^ valid for this fileptr
         EXIT    VS
 
         BIC     r14, fileptr, bufmask   ; Going to be writing at EOF ?
@@ -686,19 +683,14 @@ EnsureBufferValidForWrite Entry "r1-r2"
         EXIT
 90
         ADD     r2, extent, #1
-        ADD     r2, r2, bufmask         ; Round 0000 up to 0100
+        ADD     r2, r2, bufmask         ; Round up to nearest buffer multiple
         BICS    r2, r2, bufmask
-        BEQ     %FA99                   ; [wrapped 32 bits]
+        MOVEQ   r2, #&FFFFFFFF          ; Saturate at 4G-1
         BL      EnsureFileSize
 
         BLVS    DeallocateBuffer        ; Discard invalid buffer
         EXIT                            ; Accumulates V
 
-
-99      addr    r0, ErrorBlock_FSFileTooBig
-        BL      CopyError
-        EXIT
-
 ; +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 ;
 ; EnsureBufferValid
@@ -797,7 +789,7 @@ ExtendFileWithZeroes Entry "r0-r2, fileptr, bcb, fscb" ; Nasty temporary
         CMP     r2, extent              ; File growing ?
  [ No26bitCode
         BHI     %FT05
-        CLRV
+        CLRV                            ; Ensure VClear for extents > 2G
         EXIT
 05
  |
@@ -823,7 +815,7 @@ ExtendFileWithZeroes Entry "r0-r2, fileptr, bcb, fscb" ; Nasty temporary
 
         SUB     r14, r2, #1             ; Maps xx001..xx100 -> xx000..xx0FF
         BIC     r14, r14, bufmask       ; Map to buffer base
-        CMP     r14, fscb               ; In the same one as before ?
+        TEQ     r14, fscb               ; In the same one as before ?
         EXIT    EQ                      ; All done then ! VClear
 
 
@@ -831,7 +823,7 @@ ExtendFileWithZeroes Entry "r0-r2, fileptr, bcb, fscb" ; Nasty temporary
 
         ADD     r2, r2, bufmask         ; Reserve space on media
         BICS    r2, r2, bufmask
-        BEQ     %FA99                   ; [wrapped 32 bits; 0 case handled ^]
+        MOVEQ   r2, #&FFFFFFFF          ; Saturate at 4G-1
         BL      EnsureFileSize
         EXIT    VS
 
@@ -848,6 +840,18 @@ ExtendFileWithZeroes Entry "r0-r2, fileptr, bcb, fscb" ; Nasty temporary
         BIC     r2, r2, bufmask
 
         SUBS    r1, r14, r2             ; How much to do
+        BNE     %FT30
+
+; This is definitely a grow operation since "less than extent" was rejected earlier,
+; so the only way to end up with zero here is if 4G is required. However, the
+; interface for fsargs_WriteZeroes is defined to only take buffer multiples, so
+; split the 4G across two FS calls.
+
+        ADD     r1, bufmask, #1         ; One buffer
+        BL      ZeroFileFromPosition
+        ADD     r2, r2, r1              ; Adjust start point
+        RSB     r1, r1, #0              ; Remainder to do
+30
         BL      ZeroFileFromPosition
 
 ; In the interests of efficiency, we should really create a buffer full of
@@ -857,11 +861,6 @@ ExtendFileWithZeroes Entry "r0-r2, fileptr, bcb, fscb" ; Nasty temporary
 
         EXIT
 
-
-99      addr    r0, ErrorBlock_FSFileTooBig
-        BL      CopyError
-        EXIT
-
 ; +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 ;
 ; ZeroBufferFromPosition
@@ -905,8 +904,8 @@ ZeroBufferFromPosition Entry "r0-r1"
 ;
 ; Write zeroes to a file from a given point
 
-; In    r2 = offset in file
-;       r1 = number of bytes to zero (can be zero)
+; In    r2 = offset in file, a buffer multiple
+;       r1 = number of bytes to zero (can be zero), a buffer multiple
 
 ZeroFileFromPosition Entry "r0-r3"
 
@@ -946,7 +945,7 @@ EnsureFileSize Entry "r0, r3"
         EXITS   LS                              ; Assumes VClear in entry lr
  ]
 
-        MOV     r0, #fsargs_EnsureSize          ; r2 = new size, r3 = old extnt
+        MOV     r0, #fsargs_EnsureSize          ; r2 = new size, r3 = old extent
         LDR     r3, scb_extent
         BL      CallFSArgs