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SubjectRe: [reiserfs-dev] Re: [PATCH] sparc32: wrong type of nlink_t
On Thu, Sep 05, 2002 at 02:18:49PM -0700, jw schultz wrote:
> I'm assuming for the moment that the discussion here is
> about what to report to stat(2) and not how to deal with
> internal overflow (which should produce an error).
> So what you are suggesting is that
> <pseudocode>
> if (i.i_nlink > ST_NLINK_MAX)
> st.st_nlink = S_ISDIR(i.i_mode) ? 1 : ST_NLINK_MAX;
> </pseudocode>
> I don't know the rationale for st_nlink == 1 on directories
> but it seems to me the thing to do is st_nlink == 0 on
> overflow regardless of type. This simplifies the logic and
> eliminates the use a funky special value that gets in the
> way of supporting growth.

I believe nlink for directories and files are used differently,
and thus may have to be handled differently as well.

Amongs other things nlink on directories are used when traversing
directory-trees. If nlink=4 on a directory there must be 2
sub-directories, and you can stop looking once you've found the two.

By giving the incorrect nlink-number, applications using this
optimization will break.

Apperently some operatingsystems/filesystems (VMS?) report the special
value of nlink=1 when the information is not available, and some
applications use this information to automaticly disable the
optimization. This is why reiserfs has returned nlink=1 for directories
with more than MAX_REISERFS_NLINK subdirectories.

Now, I've just checked the source of GNU find (v4.1.7) and it does _not_
recognize nlink=1 as a special value. (It works as long as there are
less than 2^32 subdirectories though, because it is looking for -1
subdirectories and it wraps)

I'm not sure exactly what nlink is used for in userspace for regular
files, so I don't know what value should be used when the real number
doesn't fit in the interface.

(Of course new directories/hardlinks shouldn't be created at all once
the limit is exceeded, the above is only a workaround for people that
need it anyway :) )

Ragnar Kjørstad
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