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Date:   Thu, 12 Jul 2018 20:03:04 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Al Viro <viro@ZenIV.linux.org.uk>
Cc:     David Howells <dhowells@redhat.com>, linux-api@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, torvalds@linux-foundation.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 24/32] vfs: syscall: Add fsopen() to prepare for
 superblock creation [ver #9]
Message-ID: <20180712180304.GA27758@kroah.com>
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On Thu, Jul 12, 2018 at 06:20:24PM +0100, Al Viro wrote:
> 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?

/sys/kernel/config/fs/ext4/ would work, right?  Each fs "type" would be
listed there.

Anyway, the whole "write a bunch of options and then do a 'create'" is
exactly the way configfs works.  Why not use that?

thanks,

greg k-h