LFN Support for DOSEmu

The interface for LFN is done from interrupt 21h (the ms-dos interrupt), AH = 0x71, AL function number. Here is a description of each LFN functions and how to implement it. For emulating LFN calls we need to have the FAT file system mounted under Linux with file system VFAT. This is how it is done. We use the Linux Kernel to generate LFN calls. For the first step I only will implement using $_hdimage ='bootdir". That means booting from a directory, not using a hd-image.That means that LFN support is available from DOSEmu v0.98 and above only.
 

Function	Name and description
0Dh	Reset drive Description This function flushes the file system buffers and cache.  Registers  AX = 710Dh  CX = action   DX = drive number  Values for drive reset action:  0000h flush file system buffers for drive, and reset drive  0001h flush filesystem buffers and cache for drive, and reset drive  0002h remount DriveSpace volume How to implement We could call function 0Dh of interrupt 21h that does the same. (what is the difference between those two?). Action 2 will not be implemented.
39h	Create directory Description Writes a directory to the file system. Registers DS:DX -> ASCIZ long directory name (including path) How to implement We need to know where to find the directory under UNIX . Then  we call the Kernel to generate the LFN directory under that file system.
3Ah	Remove directory Description Deletes a directory from the file system. Registers DS:DX -> ASCIZ long name of directory to remove How to implement Look at function 39h.  Another good way could be to get the SFN of the directory and then call dos function 3Ah. This will remove a SFN directory (this directory is actually the one the user wants to delete). The latest sounds better, because the DOS itself should handle it as he wishes.
3Bh	Set current directory  Description Changes the current directory. Registers DS:DX -> ASCIZ long name of directory to make current How to implement The easiest way to do it, is getting the SFN of the directory and then calling AL=3Bh which is the SFN change directory. One problem could be that standard DOS supports only a 64 byte directory size.
41h	Delete file  Description Delete a group of files. Registers DS:DX -> ASCIZ long name of file to delete  SI = wild card and attributes flag   0000h wildcards are not allowed, and search attributes are          ignored   0001h wildcards are allowed, and only files with matching          names and attributes are deleted  CL = search attributes (?)  CH = must-match attributes (?) How to implement Deleting a single file is easy, I do it the easy way, transform it to SFN and then pass it back to function 41h.  When  the calling program wants to delete a few files, it would be easy to do it from Linux, but if I really wanted to do it from DOS then  I would use functions 4Eh and 4Fh to find the files, and then pass each file to function 7141h (recursive interrupts).
43h	get/set file attributes  Description Set/change the attributes of a file. Registers DS:DX -> ASCIZ long file name BL = action (CX,DI,SI) How to implement action 0-2:  (get normal attributes), by calling AX=7143h) all others  :  calling the Kernel.
47h	get current directory  Description Get current working directory. Registers DL = drive (0=current, 1=A:, 2=B: etc.) DS:DI -> Buffer for ASCIZ How to implement Check if the drive is mounted under Linux. DOS Attributes of SFN current drive. If drive is mounted under Linux, find a directory with the same attributes.
4Eh	find first file  Description Start the search of a list of files. Registers  AX = 714Eh  CL = allowable-attributes mask        (bits 0 and 5 ignored)  CH = required-attributes mask   SI = date/time format   DS:DX -> ASCIZ filespec (both "*" and "*.*" match any filename)  ES:DI -> FindData record  How to implement Find the mounted directory under Linux and use Kernel commands.
4Fh	find next file  Description After calling function 4Eh  to continue should call this function. Registers  AX = 714Fh  BX = filefind handle   SI = date/time format   ES:DI -> buffer for FindData record  How to implement The same a function 4Eh
56h	Rename file Description Long file name rename. Registers  DS:DX -> ASCIZ old file or directory name (long names allowed)  ES:DI -> ASCIZ new name (long names allowed) How to implement Find the source name in Linux , and use Kernel functions.
60h	TrueName functions Description Get the short file name for a drive or a network connection(?). Registers  CX = sub-function  DS:SI -> ASCIZ short filename or path  ES:DI -> 261-byte buffer for canonicalized long name How to implement Find the directory in the Linux tree, get information about the file (from Linux), find a file that starts with the 5 firsts chars as the wanted file and has the same attributes as found in Linux.
6Ch	Create/open file Description Create/Open/Truncate a file. Registers  BX = access mode and sharing flags (see #01782,also AX=6C00h)  CX = attributes  DX = action (see #01781)  DS:SI -> ASCIZ filename  DI = alias hint (number to append to short filename for disambiguation) How to implement Get the SFN for the file, and call function 6Ch, or others to implement this using SFN.
A0h	Get volume information  Description Gets information about a drive. Registers  AX = 71A0h  DS:DX -> ASCIZ root name (e.g. "C:\")  ES:DI -> buffer for file system name  CX = size of ES:DI buffer How to implement Most of the field could be filled by hand. If the file system is not mounted on the Linux tree, it would report that there is no0t LFN support. On Unix drives or directories, should report that searches are case sensitive.
A1h	Terminate FindFirst/FindNext  Description When a FindFirst/FindNext functions are called, they should be terminated using this function. Registers BX  =  FileHandle get from the FindFirst How to implement Using Kernel functions.
A6h	Get file information  Description Registers How to implement
A7h	Time conversion Description Description Registers How to implement
A8h	Generate short filename  Description Generate a SFN from a LFN. Registers  AX = 71A8h  DS:SI -> ASCIZ long filename (no path allowed!)  ES:DI -> buffer for ASCIZ short filename  DH = short name's format      00h 11-char directory entry/FCB filename format      01h DOS 8.3  DL = character sets      bits 7-4: short name's character set       bits 3-0: long name's character set  How to implement See TrueName functions.
A9h	Server create/open file  Description Registers How to implement
AAh	create/terminate SUBST  Description Registers How to implement

 

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