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    SubjectRe: [PATCH] umount.2: Correct the description of MNT_DETACH
    Andy Lutomirski <luto@amacapital.net> writes:

    > On Mon, Sep 29, 2014 at 6:04 PM, Eric W. Biederman
    > <ebiederm@xmission.com> wrote:
    >>
    >> 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 <ebiederm@xmission.com>
    >> ---
    >> 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.
    >
    > Want to add something like:
    >
    > MNT_DETACH on a shared mount will propagate unmount events to its peer
    > group. That means that recursively bind mounting a shared mount and
    > then unmounting that recursive bind mount will unmount all submounts
    > of the original mount. This behavior can be avoided by remounting a
    > directory with MS_REC | MS_PRIVATE before unmounting it.

    Make that any unmount on a shared mount that will propogate unmount
    events to it's peer group.

    Eric



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