[Info-vax] Looking for documentation for programming with symlinks

[John E. Malmberg]

On 11/9/2019 10:41 AM, John Reagan wrote:
> On Friday, November 8, 2019 at 7:34:50 PM UTC-5, John E. Malmberg wrote:
>> On 11/8/2019 10:13 AM, John Reagan wrote:
>>> On Friday, November 8, 2019 at 9:04:57 AM UTC-5, John E. Malmberg wrote:
>>>> Hello,
>>>>
>>>> I am looking for documentation on programming symlinks using system
>>>> services.
>>>>
>>>> Particularly the usages of:
>>>>
>>>> ATR$C_SYMLINK
>>>> ATR$S_SYMLINK
>>>>
>>>> FAB$C_SYMLINK
>>>> FAB$C_SYMBOLIC_LINK
>>>>
>>>> naml$v_symlink_in_path
>>>> naml$v_object_symlink
>>>>
>>>> I think I can figure most of it out by looking at the header files
>>>> generated by SDL.
>>>>
>>>> Regards,
>>>> -John
>>>> wb8tyw at qsl.net_work
>>>
>>> The ATR$ symbols are the F11XQP file attribute for a symlink.  The
>>> FAB$ ones are for creating/accessing a symlink.  For the NAML$ bits,
>>> I searched ALL the listings on a full Itanium build disk and found no
>>> uses of SYMLNK_IN_PATH at all.  For OBJECT_SYMLINK, I found one place
>>> in the CRTL that looks at it, but I found zero places that set it.
>>
>> While something in the CRTL has to check if a file is a symlink for the
>> difference in stat or lstat.
>>
>> In my case I need to check if the file is a symlink, and if it is, I
>> have to check to see if the symlink is to a directory.
>>
>> I am already using sys$parse and sys$search to see if the file or link
>> exists, so I am trying to get the additional information as efficiently
>> as possible.
>>
>> Regards,
>> -John
> 
> Well, from POSIX, you'd call lstat() on the file and check the
> returned mode in the stat buffer to see if S_IFLNK. That's what most of
> the ACRTL does and what any other program should do.

I may need to run some more tests on lstat() Currently I am showing in 
my tests:

$ create sys$disk:[]test."
$ create/symlink="./test" sys$disk:[]^9test.

The CRTL lstat("^9test") is returning st_mode as 100000 instead of 
120000 as expected if my test logic is correct.

I am getting the expected st_mode of 120000 for symlinks to directories.

> If you want the VMS behind-the-scenes approach (and what the CRTL
> uses at the bottom), open a channel, use a $QIO to get the IO$_ACCESS
> file characteristics longword (you'll need a FIB and an attribute
> list asking  for ATR$C_RECATTR) and look at
> 
>        8   67497                                 /*
>        8   67498                                 **  Check for a symbolic link file
>        8   67499                                 */
>        8   67500                                 if ( (recattr.fat$v_fileorg == FAT$C_SPECIAL) &&
>        8   67501                                      (recattr.fat$b_special_type == FAT$C_SYMBOLIC_LINK) )
>

I already have a $search() FAB/NAML structures, so I was hoping that I 
could just get the information there.

Regards,
-John
wb8tyw at qsl.net_work