* Btrfs st_nlink for directories
@ 2010-01-23 2:28 Neil Schemenauer
2010-01-23 20:42 ` Aneesh Kumar K. V
0 siblings, 1 reply; 3+ messages in thread
From: Neil Schemenauer @ 2010-01-23 2:28 UTC (permalink / raw)
To: linux-btrfs
Hi,
It looks like Btrfs does not follow Unix traditions for st_nlink
attribute of directories. It seems to be always one, no matter the
number of sub-directories.
Is this intentional? I couldn't find it discussed anywhere. I
gather the Mac OS HFS+ doesn't follow traditional st_nlink behavior
as well. The 'find' man page has this note:
-noleaf
Do not optimize by assuming that directories contain 2 fewer
subdirectories than their hard link count. This option is
needed when searching filesystems that do not follow the Unix
directory-link convention, such as CD-ROM or MS-DOS filesystems
or AFS volume mount points. Each directory on a normal Unix
filesystem has at least 2 hard links: its name and its `.'
entry. Additionally, its subdirectories (if any) each have a
`..' entry linked to that directory. When find is examining a
directory, after it has statted 2 fewer subdirectories than the
directory's link count, it knows that the rest of the entries in
the directory are non-directories (`leaf' files in the directory
tree). If only the files' names need to be examined, there is
no need to stat them; this gives a significant increase in
search speed.
Regards,
Neil
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: Btrfs st_nlink for directories
2010-01-23 2:28 Btrfs st_nlink for directories Neil Schemenauer
@ 2010-01-23 20:42 ` Aneesh Kumar K. V
2010-01-24 0:33 ` Chris Mason
0 siblings, 1 reply; 3+ messages in thread
From: Aneesh Kumar K. V @ 2010-01-23 20:42 UTC (permalink / raw)
To: Neil Schemenauer, linux-btrfs
On Fri, 22 Jan 2010 20:28:12 -0600, Neil Schemenauer <nas@arctrix.com> wrote:
> Hi,
>
> It looks like Btrfs does not follow Unix traditions for st_nlink
> attribute of directories. It seems to be always one, no matter the
> number of sub-directories.
>
> Is this intentional? I couldn't find it discussed anywhere. I
> gather the Mac OS HFS+ doesn't follow traditional st_nlink behavior
> as well. The 'find' man page has this note:
I have sent patches with message-id
1264279089-14913-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com
to the list. Let me know if they works for your
-aneesh
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Btrfs st_nlink for directories
2010-01-23 20:42 ` Aneesh Kumar K. V
@ 2010-01-24 0:33 ` Chris Mason
0 siblings, 0 replies; 3+ messages in thread
From: Chris Mason @ 2010-01-24 0:33 UTC (permalink / raw)
To: Aneesh Kumar K. V; +Cc: Neil Schemenauer, linux-btrfs
On Sun, Jan 24, 2010 at 02:12:59AM +0530, Aneesh Kumar K. V wrote:
> On Fri, 22 Jan 2010 20:28:12 -0600, Neil Schemenauer <nas@arctrix.com> wrote:
> > Hi,
> >
> > It looks like Btrfs does not follow Unix traditions for st_nlink
> > attribute of directories. It seems to be always one, no matter the
> > number of sub-directories.
> >
> > Is this intentional? I couldn't find it discussed anywhere. I
> > gather the Mac OS HFS+ doesn't follow traditional st_nlink behavior
> > as well. The 'find' man page has this note:
>
> I have sent patches with message-id
> 1264279089-14913-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com
> to the list. Let me know if they works for your
Thanks for taking a look at this Aneesh, but in btrfs we always have a
link count of one on directories.
It's a design decision so that we don't end up limited in the total
number of subdirs we can create. reiser3 did something similar,
switching to 1 when the link count got high. I think the other
filesystems may have added something along these lines as well by now.
Btrfs just leaves it at one all the time.
-chris
^ permalink raw reply [flat|nested] 3+ messages in thread
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