GNU bug report logs - #10733
24.0.93; w32 file truncation

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From: "Ota, Takaaki" <Takaaki.Ota <at> am.sony.com>
To: <ofv <at> wanadoo.es>
Cc: lekktu <at> gmail.com, eliz <at> gnu.org, 10733 <at> debbugs.gnu.org
Subject: bug#10733: 24.0.93; w32 file truncation
Date: Mon, 6 Feb 2012 15:43:27 -0800

Don't you need to dispose fh properly?

-Tak

Mon, 6 Feb 2012 15:27:07 -0800: Óscar Fuentes <ofv <at> wanadoo.es> wrote:

> Eli Zaretskii <eliz <at> gnu.org> writes:
> 
> [snip]
> 
> > No.  The `stat' Emacs uses is in w32.c.  What you see on
> > lib-src/ntlib.c is just a minimal subset of what we have in w32.c.
> 
> That's important. Thanks.
> 
> >> Symlinks are detected and handled specially on MSVCRT's stat. In
> >> aessence, for symlinks it uses fstat.
> >
> > But fstat probably calls GetFileInformationByHandle under the hood,
> > and we already call that function in w32.c:stat.  So maybe the fix is
> > not as ugly and inelegant as you thought.
> 
> Yup. This patch fixes the problem:
> 
> diff --git a/src/w32.c b/src/w32.c
> index f610a36..035e1f2 100644
> --- a/src/w32.c
> +++ b/src/w32.c
> @@ -3444,6 +3444,29 @@ stat (const char * path, struct stat * buf)
>  	}
>      }
>  
> +  buf->st_size = 0;
> +
> +  if ((wfd.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) &&
> +      (wfd.dwReserved0 == IO_REPARSE_TAG_SYMLINK))
> +    {
> +      HANDLE fh;
> +      BY_HANDLE_FILE_INFORMATION info;
> +
> +      if ((fh = CreateFile (name, 0, 0, NULL, OPEN_EXISTING,
> +                            FILE_FLAG_BACKUP_SEMANTICS, NULL))
> +          && GetFileInformationByHandle (fh, &info))
> +        {
> +          buf->st_size = info.nFileSizeHigh;
> +          buf->st_size <<= 32;
> +          buf->st_size += info.nFileSizeLow;
> +        }
> +      else
> +        {
> +          errno = ENOENT;
> +          return -1;
> +        }
> +    }
> +
>    if (!(NILP (Vw32_get_true_file_attributes)
>  	|| (EQ (Vw32_get_true_file_attributes, Qlocal) && is_slow_fs (name)))
>        /* No access rights required to get info.  */
> @@ -3532,9 +3555,12 @@ stat (const char * path, struct stat * buf)
>    buf->st_dev = volume_info.serialnum;
>    buf->st_rdev = volume_info.serialnum;
>  
> -  buf->st_size = wfd.nFileSizeHigh;
> -  buf->st_size <<= 32;
> -  buf->st_size += wfd.nFileSizeLow;
> +  if (! buf->st_size)
> +    {
> +      buf->st_size = wfd.nFileSizeHigh;
> +      buf->st_size <<= 32;
> +      buf->st_size += wfd.nFileSizeLow;
> +    }
>  
>    /* Convert timestamps to Unix format. */
>    buf->st_mtime = convert_time (wfd.ftLastWriteTime);
> 
> 
> Maybe it can be integrated in the
> 
> if (!(NILP(Vw32_get_true_file_attributes) ...
> 
> hence reusing the calls to CreateFile and GetFileInformationByHandle and
> shortening the patch, but as I don't know what
> Vw32_get_true_file_attributes does, preferread to follow the safe way.
> 
> However, we still have another implementation on ntlib.c.
> 
> And the fix is just for the size. Don't know if there are other
> attributes suffer from the same problem. Possibly the right thing is to
> do what MSVCRT does:
> 
> if is-symlink?
>   use fstat
> fi
> 

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