Andrey Wagin <avagin@xxxxxxxxx> writes: > 2015-03-28 1:47 GMT+03:00 Richard Weinberger <richard@xxxxxx>: >> Hi! >> >> Am 27.03.2015 um 23:35 schrieb Andrey Wagin: >>> 2015-03-28 0:42 GMT+03:00 Richard Weinberger <richard.weinberger@xxxxxxxxx>: >>>> On Fri, Mar 27, 2015 at 9:39 PM, Andrey Vagin <avagin@xxxxxxxxxx> wrote: >>>>> I don't see any reasons to hide them. This information can help to >>>>> understand errors. >>>> >>>> Because these flags are set/read only internally by the VFS. In contrast >>>> to the other flags shown by mountinfo MNT_LOCKED is not a mount option. >>> >>> But this flag is set as a result of the specified user action, when he >>> unshares userns and mntns. This flag affects visiable behaviour. >> >> It is a implicit result. Used by the VFS internally. >> If you expose it it becomes ABI and changing the behavior will be >> tricky or impossible. >> >>>> >>>> Why does it help to debug errors? >>>> How would a user know that mount() with MS_BIND returns EINVAL because >>>> the mount source is MNT_LOCKED? This information is useless for her. >>> >>> If I see lock_ro, I can be sure that mount -o remount,bind,rw /XXX will fail. >>> If I see locked, I know that this mount can't be umounted or moved >>> and can be bind-mounted only recursively. >>> >>> If a user see these flags, he can check that a mount namespace is >>> configured correctly without security issues. >>> >>> Sorry but I don't understand why you think that this information is >>> useless for users. >> >> You can only know if you know how the VFS works internally. >> If know that EINVAL from mount(2) with MS_BIND can be caused by MNT_LOCKED >> because I know the source. I bet you know the source too. But not Joey random >> admin who looks into mountinfo to figure out why something does not work. >> >> If you expose MNT_LOCKED to userspace you'll have to update also the mount(2) >> manpage with all glory details of that flag. >> >>>> If you argue like that you'd have to expose the whole VFS state to userland. >>> >>> I have not noticed other MNT_LOCK_* flags. I should think more about >>> what information are a really required for dumping mount namespaces. >>> >>>> >>>>> And this information is required for correct checkpoint/restore of mount >>>>> namespaces. >>>> >>>> Why especially MNT_LOCKED and not all the other flags used by VFS? >>> >>> My goal is to dump enough information about a mount namespace to be >>> able to restore it back later. I don't know how to do this without >>> knowledge about locked mounts. I will think. >> >> How do you plan to restore a MNT_LOCKED mount? >> IIRC we have currently no way to directly set MNT_LOCKED from userspace. > > It's the second question. The first question is how to check that we > will be able to restore what we are dumping. > > If CRIU meets something what it doesn't know how to restore, it (must) > refuses to dump this configuration. As a practical matter if the underlying directory is empty, and will remain empty MNT_LOCKED does not matter. >>>> Say MNT_DOOMED? >>> >>> Mounts with MNT_DOOMED are never shown in mountinfo, are they? >> >> It was just an example. There are other flags too, did you double check >> which ones you really need? >> >> To make the story short, my concern is that exposing such flags to userspace >> has to be well thought. :-) >> As long they are just internal we can change them as we like, as soon userspace >> depends somehow on it the pain begins. > > I'm agree with you. I'm going to think more about this. Thank you for > response. A big question from me is do you have the ability to find the user namespace of a mount namespace. Without that these mount flags do not matter. I would think getting the user namespace of mount namespace and getting the mount propgation tree correct would precede little things like worrying if the mount propagation state is correct. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
