linux-ext4 - Re: [PATCH] ioctl_getfsmap.2: document the GETFSMAP ioctl

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Message-ID: <CAG48ez1AWewJRg8gySgihn0y15jRhC6C+5DNwGsDpAhtokB=Lw@mail.gmail.com>
Date:   Mon, 8 May 2017 00:17:53 +0200
From:   Jann Horn <jannh@...gle.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     Michael Kerrisk-manpages <mtk.manpages@...il.com>,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, Linux API <linux-api@...r.kernel.org>,
        linux-man@...r.kernel.org
Subject: Re: [PATCH] ioctl_getfsmap.2: document the GETFSMAP ioctl

On Sun, May 7, 2017 at 5:58 PM, Darrick J. Wong <darrick.wong@...cle.com> wrote:
> Document the new GETFSMAP ioctl that returns the physical layout of a
> (disk-based) filesystem.
[...]
> +.B EPERM
> +This query is not allowed.

Please document the circumstances under which a query is allowed.

Also: From a quick glance at the XFS implementation, I don't see any
privilege checks. Am I missing something, or does this API permit an
unprivileged user to determine the number of physical blocks allocated
for any inode, even for inodes the user can't ordinarily see in any
way?