Re: [PATCH] fstests: generic: Add test of seek in directories

[Matthew Wilcox <willy@infradead.org>]

On Fri, Aug 28, 2026 at 09:36:10AM +1000, NeilBrown wrote:
> Add a test for consistency of readdir (getdents64) results.
> The expectation is that name which exist before a readdir starts, and
> still exist when the readdir completes, and which have not been removed
> or renamed away and re-created, should appear exactly once.
> Also if the fd on the file is closed in the middle of a readdir and
> re-opened with a seek to some offset previously reported, the same
> sequence should be reported as if the file was kept open with no
> seeking.  This last is important for nfsd.

I'm not sure it's required by POSIX:

	The behavior is unspecified if lseek() is used to set the file
	offset to a value other than zero or a value returned by a
	previous call to lseek() on the same open file description."

https://pubs.opengroup.org/onlinepubs/9799919799/functions/posix_getdents.html

We can of course require stronger semantics from Linux filesystems
than POSIX requires,  We should discuss the benefits & costs of doing so
(and I have no idea what the costs to btrfs or tmpfs might be).