At Sat, 4 Dec 2021 10:25:27 +0100, "J. Hannken-Illjes" <hannken%mailbox.org@localhost> wrote: Subject: Re: mount_union(8) vs. open(O_RDWR) > > Ok some comments: > > - union_copyup() works and is needed for regular nodes only. > > - it copies the node attributes up so checking the access on > the (copied) upper node should be sufficient. > > - the switch() on top checks for read-only mounted upper layer, > not the lower layer. Ah ha! That was not obvious to me at all. I assumed, incorrectly apparently, that (struct vop_access_args).a_vp would be the vnode for the lower layer in the case I was interested in since the upper one did not yet exist. So what is "a_vp" pointing to in the case where the file does not yet exist in the upper layer? vnodeops(9) says (for VOP_ACCESS) "The argument vp is the vnode of the file to check", but if it doesn't exist yet (i.e. hasn't been copied up yet)??? (in the "recursive" calls made by union_access() it is indeed either the upper vnode or lower vnode, depending on what is going to be used) > The attached diff just copies up in the VWRITE/VREG case and > this should be sufficient -- please give it a try. It works perfectly, thank you very much! -- Greg A. Woods <gwoods%acm.org@localhost> Kelowna, BC +1 250 762-7675 RoboHack <woods%robohack.ca@localhost> Planix, Inc. <woods%planix.com@localhost> Avoncote Farms <woods%avoncote.ca@localhost>
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