DOS Long File Name CRTL Extension

DOS Long File Name CRTL Extension

Although for the most part, the support of LFNs should be transparent when compiling, some changes in headers are necessary.

WCC/WCC386 should allow a new option, perhaps -lfn (to be decided), that predefines a __WATCOM_LFN__ macro to cause header files to allow larger values needed for long filenames. When a program is linked, there should be a WCL/WCL386/WLINK option to specify that LFN modules will be linked in to override the non-LFN clib functions. Perhaps a dos_lfn system will do the trick.

In addition to modifying older functions, some new functions could make themselves useful, such as a function to convert long filenames to short filenames. This way, the long filenames could be used in functions that only accept short filenames, without much difficulty for the programmer. It should be easy to add LFN support to any program so long as it can be compiled with OpenWatcom, as is the situation with DJGPP. Another useful feature would be to have a global int, such as _lfn_supported to be set t o 1 if there is an LFN TSR installed or 0 if there are no LFN TSRs installed.

For now, compatibility with Windows XP, NT (with NTLFN), and 2k is not an issue, but testing should be done exclusively in DOS environments; this includes pure DOS, DOSEMU, DOSBOX (does DOSLFN work in DOSBOX?, apparently not at this time), and possibly Windows 95 / 98, as long as an LFN driver functions correctly on the testing system. The functions should work both with and without an LFN driver installed in memory. After the above systems are found to be stable, work may begin to support other environmen ts, like Windows XP and 2k.

At this point in time the todo list is as followed:

• Submit a patch - Done
• Test really well for bugs with a complete clib - In Progress
• Submit bugfixes if necessary - Done
• Make it more complete if I missed some functions - In Progress (hopefully done)
• Add LFN2SFN function and other helper functions - Done
• Complete documentation - In progress
• Testing in complex programs (such as wcc itself)

Functions that still need LFN support include:

• unknown

The following values should be changed:

NAME_MAX   = 12  should be NAME_MAX   = 260
_MAX_PATH  = 144 should be _MAX_PATH  = 260
_MAX_DIR   = 130 should be _MAX_DIR   = 260
_MAX_FNAME = 9   should be _MAX_FNAME = 260
_MAX_EXT   = 5   should be _MAX_EXT   = 260
_MAX_NAME  = 13  should be _MAX_NAME  = 260

The find_t and dirent structures must contain LFN-specific data. SFN-related DOS calls use a dedicated data area (21 bytes), but LFN-related calls do not. Therefore, this data area can be used for LFN-specific data and there is no need to change the find_t or dirent structure.

The following __doslfn_dta structure is used to store the required LFN data.

typedef struct __doslfn_dta {
    unsigned short  cr_time;  /* creation time */
    unsigned short  cr_date;  /* creation date */
    unsigned short  ac_time;  /* last access time */
    unsigned short  ac_date;  /* last access date */
    unsigned long   sign;     /* LFN signature */
    unsigned short  handle;   /* LFN search handle */
} __doslfn_dta;

This structure overlaps the reserved data area (21 bytes) in both structures. It is used only internally by the C run-time library, so it is not part of the public definition.

The length of the name field in the find_t and dirent` structures is extended to support the entire long filename by changing the NAME_MAX macro. The LFN structure is a different size, but the layout is still same and only recompilation is required.

Working status for functions

Function	Header	Implementation Status
mkdir, _mkdir	direct.h	working
chdir, _chdir	direct.h	working
rmdir, _rmdir	direct.h	working
getcwd, _getdcwd	direct.h	working
opendir	direct.h	working
readdir	direct.h	working
closedir	direct.h	working
_dos_creat	dos.h	working
_dos_creatnew	dos.h	working
_dos_open	dos.h	working
_dos_findfirst	dos.h	working
_dos_findnext	dos.h	working
_dos_getfileattr	dos.h	working
_dos_setfileattr	dos.h	working
_dos_findclose	dos.h	working
access, _access	io.h	working (but not in Win2k, patches welcome)
chmod. _chmod	io.h	working
open, _open	io.h	working
sopen, _sopen	io.h	working
unlink, _unlink	io.h	working
remove	io.h	working
_findfirst	io.h	working but needs further testing
_findclose	io.h	needs further testing
_findnext	io.h	not working
execve, _execve	process.h	working (patch still to be committed)
spawnve, _spawnve	process.h	working (patch still to be committed)
stat, _stat	sys/stat.h	working
lstat. _lstat	sys/stat.h	working
fopen	stdio.h	working
rename	stdio.h	working