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 22:00:18 +0100
From:   David Howells <dhowells@...hat.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     dhowells@...hat.com, Andy Lutomirski <luto@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux API <linux-api@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jann Horn <jannh@...gle.com>, tycho@...ho.ws
Subject: Re: [PATCH 24/32] vfs: syscall: Add fsopen() to prepare for superblock creation [ver #9]

Andy Lutomirski <luto@...capital.net> wrote:

> fsconfigure(contextfd, ADD_BLOCKDEV, dfd, path, flags);
> 
> fsconfigure(contextfd, ADD_OPTION, 0, “foo=bar”, flags);

That seems okayish.  I'm not sure we need the flags, but I do want to allow
for binary data in an option.  So perhaps something like:

	int fsconfig(int fd, unsigned int type,
		     const char *key, const void *val, size_t val_len);

for example:

	fd = fsopen("ext4", FSOPEN_CLOEXEC);
	fsconfig(fd, fsconfig_blockdev, "dev.data", "/dev/sda1", ...);
	fsconfig(fd, fsconfig_blockdev, "dev.journal", "/dev/sda2", ...);
	fsconfig(fd, fsconfig_option, "user_xattr", NULL, ...);
	fsconfig(fd, fsconfig_option, "errors", "continue", ...);
	fsconfig(fd, fsconfig_option, "data", "journal", ...);
	fsconfig(fd, fsconfig_security, "selinux.context", "unconfined_u:...");
	fsconfig(fd, fsconfig_create, NULL, NULL, 0);
	mfd = fsmount(fd, FSMOUNT_CLOEXEC, MS_NOEXEC);

or:

	fd = fsopen("nfs", FSOPEN_CLOEXEC);
	fsconfig(fd, fsconfig_namespace, "user", "<usernsfd>", ...);
	fsconfig(fd, fsconfig_namespace, "net", "<netnsfd>", ...);
	fsconfig(fd, fsconfig_option, "server", "foo.com", ...);
	fsconfig(fd, fsconfig_option, "root", "/bar", ...);
	fsconfig(fd, fsconfig_option, "soft", NULL, ...);
	fsconfig(fd, fsconfig_option, "retry", "3", ...);
	fsconfig(fd, fsconfig_option, "wsize", "4096", ...);
	fsconfig(fd, fsconfig_uidmap, "dhowells", "1234", ...);
	fsconfig(fd, fsconfig_security, "selinux.context", "unconfined_u:...");
	fsconfig(fd, fsconfig_create, NULL, NULL, 0);
	mfd = fsmount(fd, FSMOUNT_CLOEXEC, MS_NOEXEC);

This does mean that userspace has to work harder, though, but it would
simplify the LSM interface internally.

Al Viro <viro@....linux.org.uk>

> First of all, block device *IS* a fucking option.

Whilst that is true, I still need to be able to separate it out for
unconverted filesystems.

David