Date: Wed, 25 Dec 2019 20:38:07 +0100 From: Florian Weimer <fw@...eb.enyo.de> To: "Theodore Y. Ts'o" <tytso@....edu> Cc: Rich Felker <dalias@...c.org>, linux-fsdevel@...r.kernel.org, musl@...ts.openwall.com, linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org Subject: Re: getdents64 lost direntries with SMB/NFS and buffer size < unknown threshold * Theodore Y. Ts'o: > 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. Sure, but Linux better provides some reasonable foundation for a libc. I mean, sure, we can read the entire directory into RAM on the first readdir, and get a fully conforming implementation this way (and as Rich noted, glibc's 32 KiB buffer tends to approximate that in practice). But that doesn't strike me as particularly useful. The POSIX requirement is really unfortunate because it leads to incorrect implementations of rm -rf which would on a compliant system and fail in practice. > 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.? I'm sure it shows up with certain directory contents on any Linux file system except for those that happen to have a separate B-tree (or equivalent) for telldir/seekdir support. And even those will have broken corner case in case of billions of directory operations. 32 bits are simply not enough storage space for the cookie. Hashing just masks the presence of these bugs, but does not eliminate them completely.
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