From:	Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: fstat works incorrectly under Windows NT
Date:	Thu, 06 Apr 2000 21:27:49 +0200
Organization:	NetVision Israel
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Wojciech Galazka wrote:
> 
> Under Windows NT the command 'ln a b' cannot produce a hard link from a file
> 'a' to a file 'b'.

Question no.1: did you compile `ln' yourself, or are you using the binary
from fil316b.zip on SimTel?  (That binary was compiled with DJGPP v2.01;
`fstat' changed since then.)

> A close inspection of the ln.c soiurce shows that the problem is in
> libc/posix/unistd/link.c.
> link() call doesn't work because the call fstat(destination file) (in this
> case file 'b') returns
> 0 in the st_dev field of statbuf struct instead of 3 (the file is on drive
> d:).

Question no.2: with what version of DJGPP did you test this?

> Consequently  the code snippet from link.cpasted below  fails
> 
>   /* Fail if path1 and path2 are on different devices */
>   if (fstat(fd2, &statbuf2) < 0) return -1;
>   if (statbuf1.st_dev != statbuf2.st_dev)

Question no.3: if `fstat' returns 0 for st_dev, and if it does that for both
files, then the above snippet should succeed, right?  So what exactly is the
problem?

> Fstat itself grabs the information for st_dev field from SFT table

No.  On NT, `fstat' is supposed to get st_dev from the IOCTL call issued by
the function _get_dev_info; the SFT is not used on NT because NT doesn't
emulate it.  Please step with a debugger into `fstat' and see whether that
this is what happens, or perhaps there's some bug.

> [SFT ] which
> Windows NT does not to fill correctly for a newly created file.
> All I could think of this for now is to manually 'update' the SFT table
> while creating the file.

Are you sure NT indeed creates the SFT in its DOS box?  AFAIK, it doesn't. 
That's why `fstat' doesn't use it: `fstat' has built-in sanity checks for the
data in the SFT, which AFAIK fail on NT.

If there is a valid SFT, `fstat' could be changed to use its info.  Please
tell what should be changed in `fstat' so that it believes the NT emulation
of the SFT.

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