autofs: add ignore mount option

Add an autofs file system mount option that can be used to provide a
generic indicator to applications that the mount entry should be ignored
when displaying mount information.

In other OSes that provide autofs and that provide a mount list to user
space based on the kernel mount list a no-op mount option ("ignore" is
the one use on the most common OS) is allowed so that autofs file system
users can optionally use it.

The idea is that it be used by user space programs to exclude autofs
mounts from consideration when reading the mounts list.

Prior to the change to link /etc/mtab to /proc/self/mounts all I needed
to do to achieve this was to use mount(2) and not update the mtab but
now that no longer works.

I know the symlinking happened a long time ago and I considered doing
this then but, at the time I couldn't remember the commonly used option
name and thought persuading the various utility maintainers would be too
hard.

But now I have a RHEL request to do this for compatibility for a widely
used product so I want to go ahead with it and try and enlist the help
of some utility package maintainers.

Clearly, without the option nothing can be done so it's at least a
start.

Link: http://lkml.kernel.org/r/154725123970.11260.6113771566924907275.stgit@pluto-themaw-net
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 1 deletions

diff --git a/fs/autofs/inode.c b/fs/autofs/inode.c
index 078992eee299..8647ecaa89fc 100644
--- a/fs/autofs/inode.c
+++ b/fs/autofs/inode.c
@@ -89,6 +89,8 @@ static int autofs_show_options(struct seq_file *m, struct dentry *root)
 		seq_printf(m, ",indirect");
 	if (sbi->flags & AUTOFS_SBI_STRICTEXPIRE)
 		seq_printf(m, ",strictexpire");
+	if (sbi->flags & AUTOFS_SBI_IGNORE)
+		seq_printf(m, ",ignore");
 #ifdef CONFIG_CHECKPOINT_RESTORE
 	if (sbi->pipe)
 		seq_printf(m, ",pipe_ino=%ld", file_inode(sbi->pipe)->i_ino);
@@ -111,7 +113,8 @@ static const struct super_operations autofs_sops = {
 };
 
 enum {Opt_err, Opt_fd, Opt_uid, Opt_gid, Opt_pgrp, Opt_minproto, Opt_maxproto,
-	Opt_indirect, Opt_direct, Opt_offset, Opt_strictexpire};
+	Opt_indirect, Opt_direct, Opt_offset, Opt_strictexpire,
+	Opt_ignore};
 
 static const match_table_t tokens = {
 	{Opt_fd, "fd=%u"},
@@ -124,6 +127,7 @@ static const match_table_t tokens = {
 	{Opt_direct, "direct"},
 	{Opt_offset, "offset"},
 	{Opt_strictexpire, "strictexpire"},
+	{Opt_ignore, "ignore"},
 	{Opt_err, NULL}
 };
 
@@ -206,6 +210,9 @@ static int parse_options(char *options,
 		case Opt_strictexpire:
 			sbi->flags |= AUTOFS_SBI_STRICTEXPIRE;
 			break;
+		case Opt_ignore:
+			sbi->flags |= AUTOFS_SBI_IGNORE;
+			break;
 		default:
 			return 1;
 		}