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

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Message-ID: <20200327051928.i5xtvskvktbugifa@mayhem.atnf.CSIRO.AU>
Date:   Fri, 27 Mar 2020 05:19:29 +0000
From:   "McIntyre, Vincent (CASS, Marsfield)" <Vincent.Mcintyre@...ro.au>
To:     Ian Kent <raven@...maw.net>
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()

One nit, below.
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;
>

--