linux-kernel - Re: [PATCH] fs: allow do_renameat2() over bind mounts of the same filesystem.

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Message-ID: <87tuwlf509.fsf@platform.sh>
Date:   Sun, 30 Aug 2020 00:42:46 +0200
From:   Florian Margaine <florian@...tform.sh>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: allow do_renameat2() over bind mounts of the same filesystem.

Matthew Wilcox <willy@...radead.org> writes:

> On Sat, Aug 29, 2020 at 11:23:34PM +0200, Florian Margaine wrote:
>> Al Viro <viro@...iv.linux.org.uk> writes:
>> 
>> > On Fri, Aug 28, 2020 at 10:40:35PM +0200, Florian Margaine wrote:
>> >> There's currently this seemingly unnecessary limitation that rename()
>> >> cannot work over bind mounts of the same filesystem,
>> >
>> > ... is absolutely deliberate - that's how you set a boundary in the
>> > tree, preventing both links and renames across it.
>> 
>> Sorry, I'm not not sure I understand what you're saying.
>
> Al's saying this is the way an administrator can intentionally prevent
> renames.

Ah, ok. Thanks!

>
>>     /*
>>      * FICLONE/FICLONERANGE ioctls enforce that src and dest files are on
>>      * the same mount. Practically, they only need to be on the same file
>>      * system.
>>      */
>>     if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
>>         return -EXDEV;
>
> clone doesn't change the contents of a file, merely how they're laid out
> on storage.  There's no particular reason for an administrator to
> prohibit clone across mount points.

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