linux-kernel - Re: [RFC][PATCH] uapi: Remove the inclusion of linux/mount.h from uapi/linux/fs.h

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Date:   Wed, 10 Aug 2022 21:01:26 +0800
From:   Ian Kent <raven@...maw.net>
To:     Florian Weimer <fweimer@...hat.com>,
        David Howells <dhowells@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <christian@...uner.io>,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] uapi: Remove the inclusion of linux/mount.h from
 uapi/linux/fs.h

On 10/8/22 17:26, Florian Weimer wrote:
> * David Howells:
>
>> We're seeing issues in autofs and xfstests whereby linux/mount.h (the UAPI
>> version) as included indirectly by linux/fs.h is conflicting with
>> sys/mount.h (there's a struct and an enum).
>>
>> Would it be possible to just remove the #include from linux/fs.h (as patch
>> below) and rely on those hopefully few things that need mount flags that don't
>> use the glibc header for them working around it by configuration?
> Wasn't <linux/mount.h> split from <linux/fs.h> relatively recently, and
> userspace is probably using <linux/fs.h> to get the mount flag
> definitions?

Not sure myself but this is in the user space kernel includes

and sys/mount.h has pretty much what linux/mount.h has plus a

few function declarations. It's almost a complete duplication.


The reality is that the enum declaration could be changed to

#defines (not a preferred approach) which leaves only the

struct mount_attr which is the difficult one to resolve.


>
> In retrospect, it would have been better to add the new fsmount stuff to
> a separate header file, so that we could include that easily from
> <sys/mount.h> on the glibc side.  Adhemerval posted a glibc patch to
> fake that (for recent compilers):
>
>    [PATCH] linux: Fix sys/mount.h usage with kernel headers
>    <https://sourceware.org/pipermail/libc-alpha/2022-August/141316.html>
>
> I think it should work reliably, so that's probably the direction we are
> going to move in.

Looked a lot more complicated than I thought it could be, enough

that I can't say if it will work so I'll take your word for it.


Ian