FAT32 Directories

[AeroASM]

I want to make a directory on the root to be stored as 8.3 filename, not Long Filename. Is my directory name limited to 8 characters or 11 characters?

EDIT: Also, if in Windows XP, I create a file which conforms to 8.3 standard, will Windows XP actually store it as "legacy" 8.3 or will it store it with LFN for the hell of it?

[thomasantony]

Hi Aero,
   I haven't read much on FAT32 but AFAIk, 8.3 is a thing of FAT12(Not sure about FAT16). I THINK they are stored as LFN itself. I will check out and let you know.

Thomas :U

[AeroASM]

I think this is what happens: all LFN records actually contain an 8.3 record at the end, so it doesn't matter (I can ignore the LFN records and just read the 8.3 one). I just wanted to verify this with someone else, though.

[thomasantony]

Hi,
I just now read the MS Docs. They say that the FAT32 dir entries contain space for 8.3 bytes only . But for LFN, a special bit combo is set in the attributes which causes it to go through other entries in order to get the whole file name

Thomas :U

[MichaelW]

I don't know about Windows XP, but for previous versions of Windows the system would generate a short name for any non-8.3 name. For short names the 8.3 applies to directories as well as files. AFAIK if you specify an 8.3 name it will be stored as an 8.3 name. For more information you could try a 16-bit DOS app that calls the LFN version of the FindFirstFile function (Interrupt 21h, function 714Eh). See Ralf Brown's Interrupt List for information on the LFN functions, and the FindData structure used by the FindFirstFile function.

An HTML version is here:

http://www.ctyme.com/rbrown.htm

And the download version here:

http://www-2.cs.cmu.edu/~ralf/files.html

I don't know of any way you can reasonably view the actual directory entries under Windows XP (even from a DOS app).

[AeroASM]

Also, MS-DOS is not case sensitive, yet when I say dir it gives the case in which I typed it in in the first place. Example: I make a file called AbC, and it shows up as AbC, but I create a file called abc and it shows up as abc. Does this mean, when reading the FAT32 filesystem, that I have to be case-sensitive with filenames?

[thomasantony]

Hi,
  FAT32 is not case-sensitive. |Its just that in MSDOS, they converted all names to uppercase. In FAT32 they don't do it but its still case-insensitive. So "FooBar.bar" and "fOObAR.BAR" are the same file and cannot reside together in the same dir.

Thomas :U

[AeroASM]

But if I store a file as FOOBAR.bar and I look in the directory entries for foobar.BAR, will I find it?

[thomasantony]

yes you will find it because you are using case-insensitive search like szCmpi.

Thomas :U

[MichaelW]

Perhaps this DOS app will help answer your questions.

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; «««««««««««««««««««««««««««««««««««««««««««««««««««««««««««««
; Quick and dirty.
; «««««««««««««««««««««««««««««««««««««««««««««««««««««««««««««
    .model small,c
    .486
    .stack

    include support.asm

.data
    LFN_FILE_INFO STRUCT
      attributes      dd 0
      dosCreationTime dw 0
      dosCreationDate dw 0
      unused1         dd 0 ; Used for Windows 9x 64-bit format
      dosAccessTime   dw 0
      dosAccessDate   dw 0
      unused2         dd 0 ; Used for Windows 9x 64-bit format
      dosWriteTime    dw 0
      dosWriteDate    dw 0
      unused3         dd 0 ; Used for Windows 9x 64-bit format
      fileSizeHigh    dd 0
      fileSizeLow     dd 0
      reserved        db 8 dup(0)
      longNameZ       db 260 dup(0)
      shortNameZ      db 14 dup(0)
    LFN_FILE_INFO ENDS

    fi LFN_FILE_INFO    <>

    fileFindHandle      dw 0     
    requiredAttributes  db 0  ; normal
    allowedAttributes   db 0  ; normal
.code
.startup
; «««««««««««««««««««««««««««««««««««««««««««««««««««««««««««««   
    mov   bx,81h              ; skip leading space
    .WHILE al != 13           ; scan command line for CR
      inc   bx
      mov   al,es:[bx]
    .ENDW   
    mov   BYTE PTR es:[bx],0  ; replace with null

    push  ds
    push  es

    mov   ax,ds
    push  es
    pop   ds
    mov   es,ax

    mov   ax,714Eh            ; LfnFindFirstFile
    mov   ch,es:requiredAttributes
    mov   cl,es:allowedAttributes
    mov   dx,82h              ; ds:dx -> filespec
    mov   di,OFFSET fi        ; es:di -> fi
    mov   si,1                ; specify DOS date/time values
    stc
    int   21h

    pop   es
    pop   ds
   
    .IF CARRY?
      .IF ax == 7100h
        print "not supported",NL
        jmp   fini
      .ELSE
        print "unexpected error",NL
        jmp   fini
      .ENDIF
    .ELSE   
      mov   fileFindHandle,ax
    .ENDIF

    print "long name = ",ADDR fi.longNameZ,NL
    print "short name = ",ADDR fi.shortNameZ,NL
   
    mov   ax,71A1h            ; LfnFindClose
    mov   bx,fileFindHandle
    int   21h
  fini:
    print NL,"Press any normal key to exit...",NL
    call waitkey
; «««««««««««««««««««««««««««««««««««««««««««««««««««««««««««««
.exit
end





[attachment deleted by admin]

[AeroASM]

It does not answer my question precisely because it is a DOS app. I am not interested in the way DOS handles it, I am interested in the way it is actually stored.

[MichaelW]

It does not answer my question precisely because it is a DOS app. I am not interested in the way DOS handles it, I am interested in the way it is actually stored.

When you run it under Windows, where do you think Windows is getting the information? The LFN Interrupt 21h functions were intended to allow DOS applications, running under Windows, access to the Windows LFN system. These are Windows functions that were not available under DOS.

After adding a DIR /x to the end of runit.bat, if I run it under Windows 2000, I get:

Code Select Expand


D:\MASMDOS\New Folder>fileinfo fileinfo.asm
long name = fileinfo.asm
short name =

Press any normal key to exit...

D:\MASMDOS\NEWFOL~1>fileinfo filewithalongname.txt
long name = filewithalongname.txt
short name = FILEWI~1.TXT

Press any normal key to exit...

D:\MASMDOS\NEWFOL~1>dir /x
Volume in drive D has no label.
Volume Serial Number is 0C52-19F9

Directory of D:\MASMDOS\NEWFOL~1

05/02/2005  10:45a      <DIR>                          .
05/02/2005  10:45a      <DIR>                          ..
05/02/2005  03:49a                   0 FILEWI~1.TXT    filewithalongname.txt
05/02/2005  03:12a                  56                 makeit.bat
05/02/2005  04:33a               1,744                 fileinfo.obj
05/02/2005  04:33a               1,951                 fileinfo.exe
05/02/2005  04:33a               6,439                 fileinfo.zip
05/02/2005  10:45a                  74                 runit.bat
05/02/2005  04:33a               2,299                 fileinfo.asm
               7 File(s)         12,563 bytes
               2 Dir(s)  32,662,487,040 bytes free

D:\MASMDOS\NEWFOL~1>pause
Press any key to continue . . .

If I change the name of fileinfo.asm to mixed case, I get:

Code Select Expand


D:\MASMDOS\New Folder>fileinfo fileinfo.asm
long name = FileInfo.asm
short name = FILEINFO.ASM

Press any normal key to exit...

D:\MASMDOS\NEWFOL~1>fileinfo filewithalongname.txt
long name = filewithalongname.txt
short name = FILEWI~1.TXT

Press any normal key to exit...

D:\MASMDOS\NEWFOL~1>dir /x
Volume in drive D has no label.
Volume Serial Number is 0C52-19F9

Directory of D:\MASMDOS\NEWFOL~1

05/02/2005  10:45a      <DIR>                          .
05/02/2005  10:45a      <DIR>                          ..
05/02/2005  03:49a                   0 FILEWI~1.TXT    filewithalongname.txt
05/02/2005  03:12a                  56                 makeit.bat
05/02/2005  04:33a               1,744                 fileinfo.obj
05/02/2005  04:33a               1,951                 fileinfo.exe
05/02/2005  04:33a               6,439                 fileinfo.zip
05/02/2005  10:45a                  74                 runit.bat
05/02/2005  04:33a               2,299 FILEINFO.ASM    FileInfo.asm
               7 File(s)         12,563 bytes
               2 Dir(s)  32,662,487,040 bytes free

D:\MASMDOS\NEWFOL~1>pause
Press any key to continue . . .


The names returned by the function exactly match the names returned by the Windows DIR command. If you modify the code to display additional fields from the structure I think you will find that they also match the corresponding information returned by DIR.

[AeroASM]

But why are not all of the short filenames displayed with dir /x?

[MichaelW]

But why are not all of the short filenames displayed with dir /x?

I think it is because there is no short name entry in the directory for files where the long name and the short name would be the same. I currently have no way to verify this for Windows 2000/XP. Under Windows 98 SE I was able to find and view the directory entries for these files using a (DOS) disk editor. It seems that Windows 98 SE handles the directory entries somewhat differently than Windows 2000/XP. For example, the files FILEINFO.OBJ and FILEINFO.ZIP have only short name entries, and these entries seem to (I did not examine every field) follow the normal DOS DIRENTRY structure, with an attribute value of 20h (archive).

Code Select Expand


DIRENTRY STRUCT
  deName          db '????????'
  deExtension     db '???'
  deAttributes    db ?
  deReserved      db 10 dup(?)
  deTime          dw ?
  deDate          dw ?
  deStartCluster  dw ?
  deFileSize      dd ?
DIRENTRY ENDS

For the files that have a long file name, the long name occupies multiple long file name directory entries, each with an attribute value of 0Fh (a value that was not defined for DOS AFAIK). The layout conforms to my most recent documentation (which was based on advance information for "Chicago", before the release of Windows 95), except each character occupies two bytes.

Code Select Expand


000001A0:  46 49 4C 45 49 4E 46 4F - 4F 42 4A 20 00 2D B3 85 FILEINFOOBJ .-¦à
000001B0:  A2 32 A2 32 00 00 24 24 - A2 32 1B 77 D0 06 00 00 ó2ó2..$$ó2 w- ..
000001C0:  46 49 4C 45 49 4E 46 4F - 5A 49 50 20 00 30 B3 85 FILEINFOZIP .0¦à
000001D0:  A2 32 A2 32 00 00 39 24 - A2 32 1C 78 27 19 00 00 ó2ó2..9$ó2 x' ..
000001E0:  42 6E 00 61 00 6D 00 65 - 00 2E 00 0F 00 37 74 00 Bn.a.m.e...¤.7t.
000001F0:  78 00 74 00 00 00 FF FF - FF FF 00 00 FF FF FF FF x.t...____..____
Physical Sector: Cyl 1, Side 230, Sector 59
00000000:  01 66 00 69 00 6C 00 65 - 00 77 00 0F 00 37 69 00  f.i.l.e.w.¤.7i.
00000010:  74 00 68 00 61 00 6C 00 - 6F 00 00 00 6E 00 67 00 t.h.a.l.o...n.g.
00000020:  46 49 4C 45 57 49 7E 31 - 54 58 54 20 00 31 B3 85 FILEWI~1TXT .1¦à
00000030:  A2 32 A2 32 00 00 2A 1E - A2 32 00 00 00 00 00 00 ó2ó2..*-ó2......


Some additional information is here.

[AeroASM]

But why are not all of the short filenames displayed with dir /x?

I think it is because there is no short name entry in the directory for files where the long name and the short name would be the same.

And so why is FILEINFO.ASM displayed?