[Samba] Missing Files/Missing Folders from an NFS Share

Jeremy Allison jra at samba.org
Thu Feb 16 20:20:27 UTC 2023

On Thu, Feb 16, 2023 at 08:46:26PM +0100, Conor Armstrong wrote:
>   I'm trying to get to the bottom of where the normal directory functions
>   differ in results for block storage compared to NFS. 
>   I created a short c script to look at the offsets generated for the
>   directory when block storage backed in comparison to NFS backed. 
>   block storage backed are always positive:
>   File: 5050, Offset: 9213006461214587617
>   File: 6567, Offset: 9218690536865144001
>   File: 4033, Offset: 9220247894244709239
>   ...
>   NFS backed are negative:
>   File: 2535, Offset: -376809161603969956
>   File: 4236, Offset: -376809161586095012
>   File: 3507, Offset: -376809161585570724
>   ...
>   The negative NFS negative offsets seem to be managed already
>   in source3/smbd/dir.c in the map_dir_offset_to_wire() function which
>   adjusts for signed/unsigned longs.
>   You mention that NFS doesn't have a working
>   seekdir()/telldir()/rewinddir(). Other than the different offset (cookie)
>   management, do you know of any other differences?
>   I had a look at the wireshark dumps. I'm getting a STATUS_PENDING shortly
>   followed by a STATUS_CANCELLED for the NFS share which are absent on the
>   block storage share.

Samba relies on being able to do offset = telldir() and then
seekdir(offset) returning us to the same position in the
directory listing.

If you think about this you'll see why. Imaginary case,
directory with files a-z. Client does findfirst with 1k
buffer, server enumerates files one by one, but when
it gets to "m" it finds it doesn't have enough room
to marshall the client response.

No worries, we saved off the 'offset = telldir()' before
doing the readdir that returned filename "m". So we
seek back to the offset before the filename "m" in
this code:

         if (NT_STATUS_EQUAL(status, STATUS_MORE_ENTRIES)) {
                 dptr_SeekDir(dirptr, prev_dirpos);
                 return status;

and return the findfirst reply with files a-l.

Now when the listing continues, it'll do so with
filename "m" etc. until the listing is done.


offset = telldir()

doesn't return us to the same position in the directory
listing, then we are broken and will not return the complete
list of files.

This is what Ralph is saying when he says that NFS is
broken w.r.t listing directories. What NFS server are
you using ?

This looks relevent:


Client then does findnext, 

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