Message-ID: <3854EB26.B9DCE883@softhome.net>
Date: Mon, 13 Dec 1999 14:48:38 +0200
From: Laurynas Biveinis <lauras AT softhome DOT net>
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To: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>,
        DJGPP Workers <djgpp-workers AT delorie DOT com>
Subject: Re: The 4th symlink patch
References: <Pine DOT SUN DOT 3 DOT 91 DOT 991213102708 DOT 29470E-100000 AT is>
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Eli Zaretskii wrote:
> Does this mean that there's no lstat.txh at all?  I don't see it in
> your last set of patches.

There is, it just managed to get out of the last patch. It is 
basically stat.txt with one sentence added.

Laurynas Biveinis
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@node lstat, io
@subheading Syntax

@example
#include <sys/stat.h>

int lstat(const char *file, struct stat *sbuf);
@end example

@subheading Description

This function obtains the status of the file @var{file} and stores
it in @var{sbuf}, which has this structure:

@example
struct  stat @{
        time_t   st_atime;     /* time of last modification */
        time_t   st_ctime;     /*            ''             */
        dev_t    st_dev;       /* The drive number (0 = a:) */
        gid_t    st_gid;       /* getgid() */
        ino_t    st_ino;       /* starting cluster or a unique identifier */
        mode_t   st_mode;      /* file mode - S_IF* and S_IRUSR/S_IWUSR */
        time_t   st_mtime;     /*            ''             */
        nlink_t  st_nlink;     /* 2 + number of subdirs, or 1 for files */
        off_t    st_size;      /* size of file in bytes */
        off_t    st_blksize;   /* the size of transfer buffer */
        uid_t    st_uid;       /* getuid() */
@};
@end example

It does not follow DJGPP symlinks, so you get the info
about symlink file itself in such case.

@subheading Return Value

Zero on success, nonzero on failure (and @var{errno} set).

@subheading Portability

@portability !ansi, posix

@subheading Example

@example
struct stat s;
lstat("data.txt", &s);
if (S_ISDIR(s.st_mode))
  printf("is directory\n");
@end example

@subheading Implementation Notes

Supplying a 100% Unix-compatible @code{f?stat()} functions under DOS is an
implementation nightmare.  The following notes describe some of the
obscure points specific to their behavior in DJGPP.

1. The @samp{drive} for character devices (like @code{con}, @code{/dev/null}
and others is returned as -1.  For drives networked by Novell Netware, it
is returned as -2.

2. The starting cluster number of a file serves as its inode number.  For
files whose starting cluster number is inaccessible (empty files, files on
networked drives, etc.) the @code{st_inode} field will be @cite{invented}
in a way which guarantees that no two different files will get the same
inode number (thus it is unique).  This invented inode will also be
different from any real cluster number of any local file.  However, only
on plain DOS, and only for local, non-empty files/directories the inode
is guaranteed to be consistent between @code{lstat}, @code{stat} and 
@code{fstat} function calls.

3. The WRITE access mode bit is set only for the user (unless the file is
read-only, hidden or system).  EXECUTE bit is set for directories,  files
which can be executed from the DOS prompt (batch files, .com, .dll and .exe
executables) or run by @code{go32-v2}.

4. Size of directories is reported as the number of its files (sans `.' and
`..' entries) multiplied by 32 bytes (the size of directory entry).  On FAT
filesystems that support the LFN API (such as Windows 9X), the reported
size of the directory accounts for additional space used to store the long
file names.

5. Time stamp for root directories is taken from the volume label entry,
if that's available; otherwise, it is reported as 1-Jan-1980.

6. The variable @code{_djstat_flags} (@pxref{_djstat_flags}) controls
what hard-to-get fields of @code{struct stat} are needed by the
application.

7. @code{lstat} should not be used to get an up-to-date info about a file
which is open and has been written to, because @code{lstat} will only
return correct data after the file is closed.  Use @code{fstat}
(@pxref{fstat}) while the file is open.  Alternatively, you can call
@code{fflush} and @code{fsync} to make the OS flush all the file's data
to the disk, before calling @code{lstat}.

8. The number of links @code{st_nlink} is always 1 for files other than
directories.  For directories, it is the number of subdirectories plus
2.  This is so that programs written for Unix that depend on this to
optimize recursive traversal of the directory tree, will still work.


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