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From:   Florian Weimer <fweimer@redhat.com>
To:     Dave Chinner <david@fromorbit.com>
Cc:     Christian Brauner <brauner@kernel.org>,
        Miklos Szeredi <miklos@szeredi.hu>,
        linux-fsdevel@vger.kernel.org, Theodore Ts'o <tytso@mit.edu>,
        Karel Zak <kzak@redhat.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org,
        Linux API <linux-api@vger.kernel.org>,
        linux-man <linux-man@vger.kernel.org>,
        LSM <linux-security-module@vger.kernel.org>,
        Ian Kent <raven@themaw.net>,
        David Howells <dhowells@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <christian@brauner.io>,
        Amir Goldstein <amir73il@gmail.com>,
        James Bottomley <James.Bottomley@hansenpartnership.com>
Subject: Re: [RFC PATCH] getting misc stats/attributes via xattr API
References: <YnEeuw6fd1A8usjj@miu.piliscsaba.redhat.com>
        <20220509124815.vb7d2xj5idhb2wq6@wittgenstein>
        <20220510005533.GA2306852@dread.disaster.area>
Date:   Tue, 10 May 2022 14:45:39 +0200
In-Reply-To: <20220510005533.GA2306852@dread.disaster.area> (Dave Chinner's
        message of "Tue, 10 May 2022 10:55:33 +1000")
Message-ID: <87bkw5d098.fsf@oldenburg.str.redhat.com>
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* Dave Chinner:

> IOWs, what Linux really needs is a listxattr2() syscall that works
> the same way that getdents/XFS_IOC_ATTRLIST_BY_HANDLE work. With the
> list function returning value sizes and being able to iterate
> effectively, every problem that listxattr() causes goes away.

getdents has issues of its own because it's unspecified what happens if
the list of entries is modified during iteration.  Few file systems add
another tree just to guarantee stable iteration.

Maybe that's different for xattrs because they are supposed to be small
and can just be snapshotted with a full copy?

Thanks,
Florian