linux-kernel - [PATCH 3/6 v1] statfs: add ST

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Message-Id: <20180506224704.14669-4-christian.brauner@ubuntu.com>
Date:   Mon,  7 May 2018 00:47:01 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     torvalds@...ux-foundation.org, tglx@...utronix.de,
        kstewart@...uxfoundation.org, gregkh@...uxfoundation.org,
        pombredanne@...b.com, linux-api@...r.kernel.org,
        Christian Brauner <christian.brauner@...ntu.com>
Subject: [PATCH 3/6 v1] statfs: add ST_UNBINDABLE

Currently userspace can only determine whether a mountpoint is unbindable
by parsing /proc/<pid>/mountinfo. It would be convenient to simply retrieve
this property with a statvfs() call.
This let's userspace avoid costly parsing, supports cases where /proc is
not mounted, and supports usecases where file descriptors to mountpoints
are passed between processes that are inspected via fstatvfs().

Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
---
v0->v1:
* non-functional changes: extend commit message
---
 fs/statfs.c            | 2 ++
 include/linux/statfs.h | 1 +
 2 files changed, 3 insertions(+)

diff --git a/fs/statfs.c b/fs/statfs.c
index 5b2a24f0f263..61b3063d3921 100644
--- a/fs/statfs.c
+++ b/fs/statfs.c
@@ -29,6 +29,8 @@ static int flags_by_mnt(int mnt_flags)
 		flags |= ST_NODIRATIME;
 	if (mnt_flags & MNT_RELATIME)
 		flags |= ST_RELATIME;
+	if (mnt_flags & MNT_UNBINDABLE)
+		flags |= ST_UNBINDABLE;
 	return flags;
 }
 
diff --git a/include/linux/statfs.h b/include/linux/statfs.h
index b336c04e793c..e1b84d0388c1 100644
--- a/include/linux/statfs.h
+++ b/include/linux/statfs.h
@@ -40,5 +40,6 @@ struct kstatfs {
 #define ST_NOATIME	(1<<10) /* do not update access times */
 #define ST_NODIRATIME	(1<<11) /* do not update directory access times */
 #define ST_RELATIME	(1<<12) /* update atime relative to mtime/ctime */
+#define ST_UNBINDABLE	(1<<17)	/* change to unbindable */
 
 #endif
-- 
2.17.0