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Re: mount_union(8) vs. open(O_RDWR)
On Thu, Dec 02, 2021 at 05:23:37PM +0100, J. Hannken-Illjes wrote:
> This behaviour comes from sys/fs/union/union_vnops.c::union_access():
> * Check access permission on the union vnode.
> * The access check being enforced is to check
> * against both the underlying vnode, and any
> * copied vnode. This ensures that no additional
> * file permissions are given away simply because
> * the user caused an implicit file copy.
> union_access(void *v)
> As the underlying node is on a ro-mounted file system this will
> always fail with EROFS if the underlying node exists.
That seems like the wrong thing, since one of the original and fairly
clear use cases for onionfs is providing a read-write layer over a
What the right thing is, I don't know. At one point I was going to try
to come up with a coherent semantic model for onionfs that satisfies
all the known use cases (or determine that none exists, which is more
likely) but that was a long time ago and I've forgotten all the
David A. Holland
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