Re: Defect in XSH readdir

[Larry Dwyer <yyyyyyyyyyy@xxxxxx>]

   When returning a directory entry for the root of a mounted file
   system, some historical implementations of readdir() return the
   file serial number of the underlying mount point, rather than of
   the root of the mounted file system.  This behavior is considered
   to be a bug, since the underlying file serial number has no
   significance to applications.

Actually, this is a bug because the serial number of the file underlying 
the mount point might conflict with the serial number of another file on 
the mounted volume.

If I was backing up a volume and I found a serial number that matched the 
ID of the mount point, I could assume that this is a hard link back to the 
mount point and save the file as a link, rather than as a file.

                Cheers,
                Larry

At 10:16 AM 6/5/2006, yyyyyy@xxxxxxxxxxx wrote:
>         Defect report from : Paul Eggert , UCLA
>
> (Please direct followup comments direct to yyyyyyyyyyyyyy@xxxxxxxxxxxxx)
>
> @ page 1197 line 37475 section readdir objection {20060605a}
>
> Problem:
>
> Edition of Specification (Year): 2004
>
> Defect code :  2. Omission
>
> With the XSI option, readdir and readdir_r are required to return a
> structure containing a file serial number, but the specification does
> not say which file serial number must be returned.  In theory, a
> conforming implementation could return a random number in this slot.
> In practice, there are issues involving symbolic links, mount points,
> and so forth, that ought to be nailed down, if only to say that the
> behavior is unspecified.  In particular, there is a common bug at a
> mount point, where readdir returns the inode number of the underlying
> file instead of the root directory of the mounted file system.
>
>
> Action:
>
> After XSI page 1197 line 37475, append the following sentence with XSI
> highlighting:
>
>    The value of the structure's d_ino member shall be the file serial
>    number of the corresponding file, except that the value is
>    unspecified for symbolic links.
>
> After XSI page 1199 line 37575 insert this paragraph:
>
>    When returning a directory entry for the root of a mounted file
>    system, some historical implementations of readdir() return the
>    file serial number of the underlying mount point, rather than of
>    the root of the mounted file system.  This behavior is considered
>    to be a bug, since the underlying file serial number has no
>    significance to applications.
end
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