linux-kernel - Re: [PATCH 4/4] autofs: add comment about autofs_mountpoint

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Message-ID: <11a106b080f743964c86e6c0dd3ce32aa5d48b1b.camel@themaw.net>
Date:   Fri, 27 Mar 2020 19:33:17 +0800
From:   Ian Kent <raven@...maw.net>
To:     "McIntyre, Vincent (CASS, Marsfield)" <Vincent.Mcintyre@...ro.au>
Cc:     Al Viro <viro@...IV.linux.org.uk>,
        autofs mailing list <autofs@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] autofs: add comment about
 autofs_mountpoint_changed()

On Fri, 2020-03-27 at 05:19 +0000, McIntyre, Vincent (CASS, Marsfield)
wrote:
> One nit, below.

Yeah, thanks for that, you effort looking at the patches is
appreciated, I'll fix it.

> Vince
> 
> On Thu, Mar 26, 2020 at 01:23:36PM +0800, Ian Kent wrote:
> > The function autofs_mountpoint_changed() is unusual, add a comment
> > about two cases for which it is used.
> > 
> > Signed-off-by: Ian Kent <raven@...maw.net>
> > ---
> > fs/autofs/root.c |   21 ++++++++++++++++++---
> > 1 file changed, 18 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/autofs/root.c b/fs/autofs/root.c
> > index 308cc49aca1d..a972bbaecb46 100644
> > --- a/fs/autofs/root.c
> > +++ b/fs/autofs/root.c
> > @@ -280,9 +280,24 @@ static struct dentry
> > *autofs_mountpoint_changed(struct path *path)
> > 	struct dentry *dentry = path->dentry;
> > 	struct autofs_sb_info *sbi = autofs_sbi(dentry->d_sb);
> > 
> > -	/*
> > -	 * If this is an indirect mount the dentry could have gone away
> > -	 * as a result of an expire and a new one created.
> > +	/* If this is an indirect mount the dentry could have gone away
> > +	 * and a new one created.
> > +	 *
> > +	 * This is unusual and I can't remember the case for which it
> > +	 * was originally added now. But a example of how this can
> 
> 'an' example
> 
> > +	 * happen is an autofs indirect mount that has the "browse"
> > +	 * option set and also has the "symlink" option in the autofs
> > +	 * map entry. In this case the daemon will remove the browse
> > +	 * directory and create a symlink as the mount (pointing to a
> > +	 * local path) leaving the struct path stale.
> > +	 *
> > +	 * Another not so obvious case is when a mount in an autofs
> > +	 * indirect mount that uses the "nobrowse" option is being
> > +	 * expired and the mount has been umounted but the mount point
> > +	 * directory remains when a stat family system call is made.
> > +	 * In this case the mount point is removed (by the daemon) and
> > +	 * a new mount triggered leading to a stale dentry in the
> > struct
> > +	 * path of the waiting process.
> > 	 */
> > 	if (autofs_type_indirect(sbi->type) && d_unhashed(dentry)) {
> > 		struct dentry *parent = dentry->d_parent;
> > 
> 
> --