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Date: Wed, 14 Sep 2016 12:28:12 -0500
From: ebiederm@...ssion.com (Eric W. Biederman)
To: Ian Kent <raven@...maw.net>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
autofs mailing list <autofs@...r.kernel.org>,
Kernel Mailing List <linux-kernel@...r.kernel.org>,
Al Viro <viro@...IV.linux.org.uk>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
Omar Sandoval <osandov@...ndov.com>
Subject: Re: [PATCH 3/4] autofs - make mountpoint checks namespace aware
Ian Kent <raven@...maw.net> writes:
> If an automount mount is clone(2)ed into a file system that is
> propagation private, when it later expires in the originating
> namespace subsequent calls to autofs ->d_automount() for that
> dentry in the original namespace will return ELOOP until the
> mount is manually umounted in the cloned namespace.
>
> In the same way, if an autofs mount is triggered by automount(8)
> running within a container the dentry will be seen as mounted in
> the root init namespace and calls to ->d_automount() in that namespace
> will return ELOOP until the mount is umounted within the container.
>
> Also, have_submounts() can return an incorect result when a mount
> exists in a namespace other than the one being checked.
Overall this appears to be a fairly reasonable set of changes. It does
increase the expense when an actual mount point is encountered, but if
these are the desired some increase in cost when a dentry is a
mountpoint is unavoidable.
May I ask the motiviation for this set of changes? Reading through the
changes I don't grasp why we want to change the behavior of autofs.
What problem is being solved? What are the benefits?
Eric
> Signed-off-by: Ian Kent <raven@...maw.net>
> Cc: Al Viro <viro@...IV.linux.org.uk>
> Cc: Eric W. Biederman <ebiederm@...ssion.com>
> Cc: Omar Sandoval <osandov@...ndov.com>
> ---
> fs/autofs4/dev-ioctl.c | 2 +-
> fs/autofs4/expire.c | 4 ++--
> fs/autofs4/root.c | 30 +++++++++++++++---------------
> fs/autofs4/waitq.c | 2 +-
> 4 files changed, 19 insertions(+), 19 deletions(-)
>
> diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c
> index c7fcc74..0024e25 100644
> --- a/fs/autofs4/dev-ioctl.c
> +++ b/fs/autofs4/dev-ioctl.c
> @@ -564,7 +564,7 @@ static int autofs_dev_ioctl_ismountpoint(struct file *fp,
>
> devid = new_encode_dev(dev);
>
> - err = have_submounts(path.dentry);
> + err = have_local_submounts(path.dentry);
>
> if (follow_down_one(&path))
> magic = path.dentry->d_sb->s_magic;
> diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
> index d8e6d42..7cc34ef 100644
> --- a/fs/autofs4/expire.c
> +++ b/fs/autofs4/expire.c
> @@ -236,7 +236,7 @@ static int autofs4_tree_busy(struct vfsmount *mnt,
> * count for the autofs dentry.
> * If the fs is busy update the expiry counter.
> */
> - if (d_mountpoint(p)) {
> + if (is_local_mountpoint(p)) {
> if (autofs4_mount_busy(mnt, p)) {
> top_ino->last_used = jiffies;
> dput(p);
> @@ -280,7 +280,7 @@ static struct dentry *autofs4_check_leaves(struct vfsmount *mnt,
> while ((p = get_next_positive_dentry(p, parent))) {
> pr_debug("dentry %p %pd\n", p, p);
>
> - if (d_mountpoint(p)) {
> + if (is_local_mountpoint(p)) {
> /* Can we umount this guy */
> if (autofs4_mount_busy(mnt, p))
> continue;
> diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
> index fa84bb8..4150ad6 100644
> --- a/fs/autofs4/root.c
> +++ b/fs/autofs4/root.c
> @@ -123,7 +123,7 @@ static int autofs4_dir_open(struct inode *inode, struct file *file)
> * it.
> */
> spin_lock(&sbi->lookup_lock);
> - if (!d_mountpoint(dentry) && simple_empty(dentry)) {
> + if (!is_local_mountpoint(dentry) && simple_empty(dentry)) {
> spin_unlock(&sbi->lookup_lock);
> return -ENOENT;
> }
> @@ -370,28 +370,28 @@ static struct vfsmount *autofs4_d_automount(struct path *path)
>
> /*
> * If the dentry is a symlink it's equivalent to a directory
> - * having d_mountpoint() true, so there's no need to call back
> - * to the daemon.
> + * having is_local_mountpoint() true, so there's no need to
> + * call back to the daemon.
> */
> if (d_really_is_positive(dentry) && d_is_symlink(dentry)) {
> spin_unlock(&sbi->fs_lock);
> goto done;
> }
>
> - if (!d_mountpoint(dentry)) {
> + if (!is_local_mountpoint(dentry)) {
> /*
> * It's possible that user space hasn't removed directories
> * after umounting a rootless multi-mount, although it
> - * should. For v5 have_submounts() is sufficient to handle
> - * this because the leaves of the directory tree under the
> - * mount never trigger mounts themselves (they have an autofs
> - * trigger mount mounted on them). But v4 pseudo direct mounts
> - * do need the leaves to trigger mounts. In this case we
> - * have no choice but to use the list_empty() check and
> - * require user space behave.
> + * should. For v5 have_local_submounts() is sufficient to
> + * handle this because the leaves of the directory tree under
> + * the mount never trigger mounts themselves (they have an
> + * autofs trigger mount mounted on them). But v4 pseudo
> + * direct mounts do need the leaves to trigger mounts. In
> + * this case we have no choice but to use the list_empty()
> + * check and require user space behave.
> */
> if (sbi->version > 4) {
> - if (have_submounts(dentry)) {
> + if (have_local_submounts(dentry)) {
> spin_unlock(&sbi->fs_lock);
> goto done;
> }
> @@ -431,7 +431,7 @@ static int autofs4_d_manage(struct dentry *dentry, bool rcu_walk)
>
> /* The daemon never waits. */
> if (autofs4_oz_mode(sbi)) {
> - if (!d_mountpoint(dentry))
> + if (!is_local_mountpoint(dentry))
> return -EISDIR;
> return 0;
> }
> @@ -460,7 +460,7 @@ static int autofs4_d_manage(struct dentry *dentry, bool rcu_walk)
>
> if (ino->flags & AUTOFS_INF_WANT_EXPIRE)
> return 0;
> - if (d_mountpoint(dentry))
> + if (is_local_mountpoint(dentry))
> return 0;
> inode = d_inode_rcu(dentry);
> if (inode && S_ISLNK(inode->i_mode))
> @@ -487,7 +487,7 @@ static int autofs4_d_manage(struct dentry *dentry, bool rcu_walk)
> * we can avoid needless calls ->d_automount() and avoid
> * an incorrect ELOOP error return.
> */
> - if ((!d_mountpoint(dentry) && !simple_empty(dentry)) ||
> + if ((!is_local_mountpoint(dentry) && !simple_empty(dentry)) ||
> (d_really_is_positive(dentry) && d_is_symlink(dentry)))
> status = -EISDIR;
> }
> diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
> index 431fd7e..911f4d5 100644
> --- a/fs/autofs4/waitq.c
> +++ b/fs/autofs4/waitq.c
> @@ -333,7 +333,7 @@ static int validate_request(struct autofs_wait_queue **wait,
> dentry = new;
> }
> }
> - if (have_submounts(dentry))
> + if (have_local_submounts(dentry))
> valid = 0;
>
> if (new)
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