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

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Date:   Thu, 12 Jul 2018 18:20:24 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     David Howells <dhowells@...hat.com>, linux-api@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 24/32] vfs: syscall: Add fsopen() to prepare for
 superblock creation [ver #9]

On Thu, Jul 12, 2018 at 07:15:05PM +0200, Greg KH wrote:
> On Tue, Jul 10, 2018 at 11:44:09PM +0100, David Howells wrote:
> > Provide an fsopen() system call that starts the process of preparing to
> > create a superblock that will then be mountable, using an fd as a context
> > handle.  fsopen() is given the name of the filesystem that will be used:
> > 
> > 	int mfd = fsopen(const char *fsname, unsigned int flags);
> > 
> > where flags can be 0 or FSOPEN_CLOEXEC.
> > 
> > For example:
> > 
> > 	sfd = fsopen("ext4", FSOPEN_CLOEXEC);
> > 	write(sfd, "s /dev/sdb1"); // note I'm ignoring write's length arg
> > 	write(sfd, "o noatime");
> > 	write(sfd, "o acl");
> > 	write(sfd, "o user_attr");
> > 	write(sfd, "o iversion");
> > 	write(sfd, "o ");
> > 	write(sfd, "r /my/container"); // root inside the fs
> > 	write(sfd, "x create"); // create the superblock
> 
> Ugh, creating configfs again in a syscall form?  I know people love
> file descriptors, but can't you do this with a configfs entry instead if
> you really want to do this type of thing from userspace in this type of
> "style"?
> 
> Why reinvent the wheel again?

The damn thing REALLY, REALLY depends upon the fs type.  How would
you map it on configfs?