Linux-CIFS Archive on lore.kernel.org
 help / color / Atom feed
From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: Rich Felker <dalias@libc.org>
Cc: Florian Weimer <fw@deneb.enyo.de>,
	linux-fsdevel@vger.kernel.org, musl@lists.openwall.com,
	linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org,
	linux-cifs@vger.kernel.org
Subject: Re: [musl] getdents64 lost direntries with SMB/NFS and buffer size < unknown threshold
Date: Thu, 21 Nov 2019 12:54:18 -0500
Message-ID: <20191121175418.GI4262@mit.edu> (raw)
In-Reply-To: <20191120205913.GD16318@brightrain.aerifal.cx>

On Wed, Nov 20, 2019 at 03:59:13PM -0500, Rich Felker wrote:
> 
> POSIX only allows both behaviors (showing or not showing) the entry
> that was deleted. It does not allow deletion of one entry to cause
> other entries not to be seen.

Agreed, but POSIX requires this of *readdir*.  POSIX says nothing
about getdents64(2), which is Linux's internal implementation which is
exposed to a libc.

So we would need to see what is exactly going on at the interfaces
between the VFS and libc, the nfs client code and the VFS, the nfs
client code and the nfs server, and possibly the behavior of the nfs
server.

First of all.... you can't reproduce this on anything other than with
NFS, correct?  That is, does it show up if you are using ext4, xfs,
btrfs, etc.?

Secondly, have you tried this on more than one NFS server
implementation?

Finally, can you capture strace logs and tcpdump logs of the
communication between the NFS client and server code?

> > But many file systems simply provide not the necessary on-disk data
> > structures which are need to ensure stable iteration in the face of
> > modification of the directory.  There are hacks, of course, such as
> > compacting the on-disk directory only on file creation, which solves
> > the file removal case.

Oh, that's not the worst of it.  You have to do a lot more if the file
system needs to support telldir/seekdir, and if you want to export the
file system over NFS.  If you are using anything other than a linear
linked list implementation for your directory, you have to really turn
sommersaults to make sure things work (and work efficiently) in the
face of, say, node splits of you are using some kind of tree structure
for your directory.

Most file systems do get this right, at least if they hope to be
safely able to be exportable via NFS, or via CIFS using Samba.

       	       	  	     	      	 - Ted

  reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-20  0:15 Rich Felker
2019-11-20 19:57 ` [musl] " Florian Weimer
2019-11-20 20:59   ` Rich Felker
2019-11-21 17:54     ` Theodore Y. Ts'o [this message]
2019-12-25 19:38       ` Florian Weimer
2019-12-26  3:56         ` Theodore Y. Ts'o

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191121175418.GI4262@mit.edu \
    --to=tytso@mit.edu \
    --cc=dalias@libc.org \
    --cc=fw@deneb.enyo.de \
    --cc=linux-cifs@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-nfs@vger.kernel.org \
    --cc=musl@lists.openwall.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-CIFS Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-cifs/0 linux-cifs/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-cifs linux-cifs/ https://lore.kernel.org/linux-cifs \
		linux-cifs@vger.kernel.org
	public-inbox-index linux-cifs

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-cifs


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git