linux-kernel - Re: [PATCH 07/14] Implement fsopen() to prepare for a mount

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Message-ID: <6167.1494513034@warthog.procyon.org.uk>
Date:   Thu, 11 May 2017 15:30:34 +0100
From:   David Howells <dhowells@...hat.com>
To:     Sargun Dhillon <sargun@...gun.me>
Cc:     dhowells@...hat.com, mszeredi@...hat.com, viro@...iv.linux.org.uk,
        jlayton@...hat.com, linux-fsdevel@...r.kernel.org,
        linux-nfs@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/14] Implement fsopen() to prepare for a mount

Sargun Dhillon <sargun@...gun.me> wrote:

> Instead of string based configuration, does it perhaps make sense to
> pass in structured mount data? Something like:

I don't think it helps particularly.

> enum mount_command_id {
>     MOUNT_OPTION_STR,
>     MOUNT_SET_USER_NS
> };
> 
> struct mount_attr {
>    __u64 command_id;
>    union {
>        char option_str[4095];
>        char mount_source[PATH_MAX];

Why limit the option size to 4096?  I can see situations where it might be
necessary to hand in a bigger blob - giving cifs a Microsoft Kerberos PAC for
example.

>        struct {
>            __u32 user_ns_fd

There are more than just that namespace that could be relevant.

>        }
>    }
> }
> 
> It seems a lot less error prone to me.

Not really.  The only real difference is how one selects what action is
intended and how one determines the length.  write() has a length parameter.

David