[Issue 1000775] New: Hard links to directories

[Issue 1000775] New: Hard links to directories

[bugzilla-daemon]

http://bugzilla.ecoscentric.com/show_bug.cgi?id=1000775

           Summary: Hard links to directories
           Product: eCos
           Version: CVS
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: normal
         Component: Filesystem support
        AssignedTo: jifl@ecoscentric.com
        ReportedBy: wry@ecoscentric.com
         QAContact: ecos-bugs@ecos.sourceware.org
             Class: Advice Request


In working on YAFFS I found myself considering the question of hard links to
directories. Operating on the premise that such things are mind-bending
abominations, a nightmare to implement correctly, and in any event rarely
actually useful, I looked into whether or not we actually forbid them. Well,
fileio makes no attempt to off its own bat, but then for it to do so would be
expensive (add a call to stat within link?), so one would argue that it should
be up to the individual filesystems to check and enforce. (I'm going to forbid
them in YAFFS on the grounds that it asserted when I tried to rmdir such a
link, and I don't currently know enough about its internals to see whether this
is can be usefully supported in a reasonable time.)

Of the filesystems in eCos, romfs is obviously uninteresting, and fatfs doesn't
allow any links. The other two - ramfs and jffs2 - appear to make no attempt to
catch directory hard links, and I suspect that if somebody was ever to be mad
enough to try, they'd trip over all sorts of bugs. It should be pretty
straightforward to patch in such proscriptions, but before I do so I thought
I'd open this ticket in case anybody else wanted to comment...


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[Bug 1000775] Hard links to directories

[bugzilla-daemon]

http://bugzilla.ecoscentric.com/show_bug.cgi?id=1000775


Andrew Lunn <andrew.lunn@ascom.ch> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrew.lunn@ascom.ch




--- Comment #1 from Andrew Lunn <andrew.lunn@ascom.ch>  2009-05-20 13:19:44 ---
Looking at ramfs, i think it is supported. However the test cases don't test
it, The tests don't even test regular links!

Looking at jffs2, i think it is supported. However the test cases don't test
it, The tests don't even test regular links!

So i guess the first step it to add test for regular links and see if they
work.
Then try links to directories. You might be surprised!


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[Bug 1000775] Hard links to directories

[bugzilla-daemon]

http://bugzilla.ecoscentric.com/show_bug.cgi?id=1000775





--- Comment #2 from Andrew Lunn <andrew.lunn@ascom.ch>  2009-05-20 13:21:42 ---
You should also take this over to ecos-devel. Only people subscribed to
ecos-bugs@ecos.sourceware.org currently know of this discussion.

In fact, bugzilla is probably the wrong place altogether! 


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[Issue 1000775] Hard links to directories

[bugzilla-daemon]

http://bugzilla.ecoscentric.com/show_bug.cgi?id=1000775


Ross Younger <wry@ecoscentric.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |NOTABUG




--- Comment #3 from Ross Younger <wry@ecoscentric.com>  2009-05-28 15:34:02 ---
There was some discussion on ecos-devel.

Nick wrote:
> In eCos, support for hard directory links should generally be a
> filesystem property. If a particular filesystem can deal with the
> consequences the they should be passed through the other layers
> without comment. For YAFFS, I suspect that they should not be
> permitted.

I'm therefore not going to change any other filesystem, nor fileio itself.
YAFFS would require a bit of brain surgery to handle them correctly, so I've
opted to disallow them until such time (if ever) as there's a need.

Nobody need to anything, so I'm closing this ticket.


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