linux-kernel - Re: [PATCH 24/32] vfs: syscall: Add fsopen() to prepare for superblock creation [ver #9]

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Message-Id: <611054C7-D6E8-4C89-958E-3128C9305E1E@amacapital.net>
Date:   Thu, 12 Jul 2018 16:21:35 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     David Howells <dhowells@...hat.com>
Cc:     "Theodore Y. Ts'o" <tytso@....edu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux API <linux-api@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH 24/32] vfs: syscall: Add fsopen() to prepare for superblock creation [ver #9]



> On Jul 12, 2018, at 3:54 PM, David Howells <dhowells@...hat.com> wrote:
> 
> Theodore Y. Ts'o <tytso@....edu> wrote:
> 
>> So maybe the answer is that you open /dev/sda1 and /dev/sda2 and then
>> pass the file descriptors to the fsopen object?  We can require that
>> the fd's be opened with O_RDWR and O_EXCL, which has the benefit where
>> if you have multiple block devices, you know *which* block device had
>> a problem with being grabbed for an exclusive open.
> 
> Would that mean then that doing:
> 
>    mount /dev/sda3 /a
>    mount /dev/sda3 /b
> 
> would then fail on the second command because /dev/sda3 is already open
> exclusively?
> 

I tend to think that this *should* fail using the new API.  The semantics of the second mount request are bizarre at best.