From: ebiederm@xmission.com (Eric W. Biederman) Subject: [PATCH] umount.2: Correct the description of MNT_DETACH Date: Mon, 29 Sep 2014 18:04:05 -0700 Message-ID: <87lhp12a2i.fsf@x220.int.ebiederm.org> Mime-Version: 1.0 Content-Type: text/plain Cc: Andy Lutomirski , Andrey Wagin , , Al Viro , To: Michael Kerrisk Return-path: Received: from out01.mta.xmission.com ([166.70.13.231]:33875 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752976AbaI3BEc (ORCPT ); Mon, 29 Sep 2014 21:04:32 -0400 Sender: linux-fsdevel-owner@vger.kernel.org List-ID: I recently realized that I had been reasoning improperly about what umount(MNT_DETACH) did based on an insufficient description in the umount.2 man page, that matched my intuition but not the implementation. When there are no submounts MNT_DETACH is essentially harmless to applications. Where there are submounts MNT_DETACH changes what is visible to applications using the detach directories. Signed-off-by: Eric W. Biederman --- man2/umount.2 | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/man2/umount.2 b/man2/umount.2 index 5ff88152c738..aea39d8306fe 100644 --- a/man2/umount.2 +++ b/man2/umount.2 @@ -66,9 +66,10 @@ This can cause data loss. (Only for NFS mounts.) .TP .BR MNT_DETACH " (since Linux 2.4.11)" -Perform a lazy unmount: make the mount point unavailable for -new accesses, and actually perform the unmount when the mount point -ceases to be busy. +Perform a lazy unmount: make the mount point unavailable for new +accesses, immediately disconnect the filesystem and all filesystems +mounted below it from each other and from the mount table, and +actually perform the unmount when the mount point ceases to be busy. .TP .BR MNT_EXPIRE " (since Linux 2.6.8)" Mark the mount point as expired. -- 1.9.1