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Message-ID: <20230925-total-debatten-2a1f839fde5a@brauner>
Date: Mon, 25 Sep 2023 15:04:40 +0200
From: Christian Brauner <brauner@...nel.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: Miklos Szeredi <mszeredi@...hat.com>,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-api@...r.kernel.org, linux-man@...r.kernel.org,
linux-security-module@...r.kernel.org, Karel Zak <kzak@...hat.com>,
Ian Kent <raven@...maw.net>,
David Howells <dhowells@...hat.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <christian@...uner.io>,
Amir Goldstein <amir73il@...il.com>
Subject: Re: [RFC PATCH 2/3] add statmnt(2) syscall
On Mon, Sep 25, 2023 at 02:57:31PM +0200, Arnd Bergmann wrote:
> On Wed, Sep 13, 2023, at 17:22, Miklos Szeredi wrote:
>
> > asmlinkage long sys_fstatfs64(unsigned int fd, size_t sz,
> > struct statfs64 __user *buf);
> > +asmlinkage long sys_statmnt(u64 mnt_id, u64 mask,
> > + struct statmnt __user *buf, size_t bufsize,
> > + unsigned int flags);
>
> This definition is problematic on 32-bit architectures for two
> reasons:
>
> - 64-bit register arguments are passed in pairs of registers
> on two architectures, so anything passing those needs to
> have a separate entry point for compat syscalls on 64-bit
> architectures. I would suggest also using the same one on
> 32-bit ones, so you don't rely on the compiler splitting
> up the long arguments into pairs.
>
> - There is a limit of six argument registers for system call
> entry points, but with two pairs and three single registers
> you end up with seven of them.
>
> The listmnt syscall in patch 3 also has the first problem,
> but not the second.
Both fields could also just be moved into the struct itself just like we
did for clone3() and others.
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