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SubjectRe: Do we really need d_weak_revalidate???
On Mon, Aug 21 2017, Ian Kent wrote:

>>
>> A mount isn't triggered by kern_path(pathname, 0, &path).
>> That '0' would need to include one of
>> LOOKUP_PARENT | LOOKUP_DIRECTORY |
>> LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT
>>
>> to trigger an automount (otherwise you just get -EISDIR).
>
> It's perfectly sensible to think that but there is a case where a
> a mount is triggered when using kern_path().
>
> The EISDIR return occurs for positive dentrys, negative dentrys
> will still trigger an automount (which is autofs specific,
> indirect mount map using nobrowse option, the install default).

Ok, I understand this better now. This difference between direct and
indirect mounts is slightly awkward. It is visible from user-space, but
not elegant to document.
When you use O_PATH to open a direct automount that has not already been
triggered, the open returns the underlying directory (and fstatfs
confirms that it is AUTOFS_SUPER_MAGIC). When you use O_PATH on
an indirect automount, it *will* trigger the automount when "nobrowse" is
in effect, but it won't when "browse" is in effect.

So we cannot just say "O_PATH doesn't trigger automounts", which is
essentially what I said in

https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=97a45d02e6671482e8b2cdcce3951930bf6bdb94

It might be possible to modify automount so that it was more consistent
- i.e. if the point is triggered by a mkdir has been done, just to the
mkdir. If it is triggered after a mkdir has been done, do the mount. I
guess that might be racy, and in any case is hard to justify.

Maybe I should change it to be about "direct automounts", and add a note
that indirect automounts aren't so predictable.

But back to my original issue of wanting to discard
kern_path_mountpoint, what would you think of the following approach -
slight revised from before.

Thanks,
NeilBrown

diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
index beef981aa54f..7663ea82e68d 100644
--- a/fs/autofs4/autofs_i.h
+++ b/fs/autofs4/autofs_i.h
@@ -135,10 +135,13 @@ static inline struct autofs_info *autofs4_dentry_ino(struct dentry *dentry)
/* autofs4_oz_mode(): do we see the man behind the curtain? (The
* processes which do manipulations for us in user space sees the raw
* filesystem without "magic".)
+ * A process performing certain ioctls can get temporary oz status.
*/
+extern struct task_struct *autofs_tmp_oz;
static inline int autofs4_oz_mode(struct autofs_sb_info *sbi)
{
- return sbi->catatonic || task_pgrp(current) == sbi->oz_pgrp;
+ return sbi->catatonic || task_pgrp(current) == sbi->oz_pgrp ||
+ autofs_tmp_oz == current;
}

struct inode *autofs4_get_inode(struct super_block *, umode_t);
diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c
index dd9f1bebb5a3..d76401669a20 100644
--- a/fs/autofs4/dev-ioctl.c
+++ b/fs/autofs4/dev-ioctl.c
@@ -200,6 +200,20 @@ static int autofs_dev_ioctl_protosubver(struct file *fp,
return 0;
}

+struct task_struct *autofs_tmp_oz;
+int kern_path_oz(const char *pathname, int flags, struct path *path)
+{
+ static DEFINE_MUTEX(autofs_oz);
+ int err;
+
+ mutex_lock(&autofs_oz);
+ autofs_tmp_oz = current;
+ err = kern_path(pathname, flags, path);
+ autofs_tmp_oz = NULL;
+ mutex_unlock(&autofs_oz);
+ return err;
+}
+
/* Find the topmost mount satisfying test() */
static int find_autofs_mount(const char *pathname,
struct path *res,
@@ -209,7 +223,8 @@ static int find_autofs_mount(const char *pathname,
struct path path;
int err;

- err = kern_path_mountpoint(AT_FDCWD, pathname, &path, 0);
+ err = kern_path_oz(pathname, 0, &path);
+
if (err)
return err;
err = -ENOENT;
@@ -552,8 +567,7 @@ static int autofs_dev_ioctl_ismountpoint(struct file *fp,

if (!fp || param->ioctlfd == -1) {
if (autofs_type_any(type))
- err = kern_path_mountpoint(AT_FDCWD,
- name, &path, LOOKUP_FOLLOW);
+ err = kern_path_oz(name, LOOKUP_FOLLOW, &path);
else
err = find_autofs_mount(name, &path,
test_by_type, &type);[unhandled content-type:application/pgp-signature]
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