Re: [PATCH 3/9] VFS: Introduce a mount context

From: David Howells <dhowells@redhat.com>
To: Joe Perches <joe@perches.com>
Cc: dhowells@redhat.com, Jeff Layton <jlayton@poochiereds.net>,
	viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
	linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org,
	mszeredi@redhat.com
Subject: Re: [PATCH 3/9] VFS: Introduce a mount context
Date: Wed, 03 May 2017 19:37:41 +0100	[thread overview]
Message-ID: <4597.1493836661@warthog.procyon.org.uk> (raw)
In-Reply-To: <1493835998.22125.15.camel@perches.com>

Joe Perches <joe@perches.com> wrote:

> krealloc would probably be more efficient and possible
> readable as likely there's already padding in the original
> allocation.

The problem is if krealloc() fails: you've lost all those pointers to things
you then need to free.

> Are there no locking constraints?

Generally, no, not until you do the ->mount() op.  Also remounting needs a
lock, but that's already done with the sb->s_umount lock.

However, that said, if you do:

	fd = fsopen("foofs");
	write(fd, "o foo=bar", ...);
	fsmount(fd, "/foo");

then the fsmount() and write() calls have to lock against other fsmount() and
write() calls.  I use the inode lock for this.  [Note that it probably should
be interruptible rather than just killable, but there's no primitive for that
as yet].

David