From: Andrew Morton <akpm@linux-foundation.org>
To: Chuck Lever <cel@kernel.org>
Cc: hughd@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v1] shmem: stable directory cookies
Date: Tue, 2 May 2023 17:12:28 -0700 [thread overview]
Message-ID: <20230502171228.57a906a259172d39542e92fb@linux-foundation.org> (raw)
In-Reply-To: <168175931561.2843.16288612382874559384.stgit@manet.1015granger.net>
On Mon, 17 Apr 2023 15:23:10 -0400 Chuck Lever <cel@kernel.org> wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
>
> The current cursor-based directory cookie mechanism doesn't work
> when a tmpfs filesystem is exported via NFS. This is because NFS
> clients do not open directories: each READDIR operation has to open
> the directory on the server, read it, then close it. The cursor
> state for that directory, being associated strictly with the opened
> struct file, is then discarded.
>
> Directory cookies are cached not only by NFS clients, but also by
> user space libraries on those clients. Essentially there is no way
> to invalidate those caches when directory offsets have changed on
> an NFS server after the offset-to-dentry mapping changes.
>
> The solution we've come up with is to make the directory cookie for
> each file in a tmpfs filesystem stable for the life of the directory
> entry it represents.
>
> Add a per-directory xarray. shmem_readdir() uses this to map each
> directory offset (an loff_t integer) to the memory address of a
> struct dentry.
>
How have people survived for this long with this problem?
It's a lot of new code - can we get away with simply disallowing
exports of tmpfs?
How can we maintain this? Is it possible to come up with a test
harness for inclusion in kernel selftests?
next prev parent reply other threads:[~2023-05-03 0:12 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-17 19:23 Chuck Lever
2023-04-20 18:52 ` Jeff Layton
2023-04-20 20:12 ` Chuck Lever III
2023-05-03 0:12 ` Andrew Morton [this message]
2023-05-03 0:43 ` Chuck Lever III
2023-05-04 17:21 ` Jeff Layton
2023-05-04 20:21 ` Benjamin Coddington
2023-05-05 5:06 ` kernel test robot
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