Konstantin Belousov 140dedb81c The r241025 fixed the case when a binary, executed from nullfs mount, ... was still possible to open for write from the lower filesystem. There is a symmetric situation where the binary could already has file descriptors opened for write, but it can be executed from the nullfs overlay. Handle the issue by passing one v_writecount reference to the lower vnode if nullfs vnode has non-zero v_writecount. Note that only one write reference can be donated, since nullfs only keeps one use reference on the lower vnode. Always use the lower vnode v_writecount for the checks. Introduce the VOP_GET_WRITECOUNT to read v_writecount, which is currently always bypassed to the lower vnode, and VOP_ADD_WRITECOUNT to manipulate the v_writecount value, which manages a single bypass reference to the lower vnode. Caling the VOPs instead of directly accessing v_writecount provide the fix described in the previous paragraph. Tested by: pho MFC after: 3 weeks		2012-11-02 13:56:36 +00:00
..
null.h	Allow shared lookups for nullfs mounts, if lower filesystem supports	2012-09-09 19:20:23 +00:00
null_subr.c	Allow shared lookups for nullfs mounts, if lower filesystem supports	2012-09-09 19:20:23 +00:00
null_vfsops.c	Allow shared lookups for nullfs mounts, if lower filesystem supports	2012-09-09 19:20:23 +00:00
null_vnops.c	The r241025 fixed the case when a binary, executed from nullfs mount,	2012-11-02 13:56:36 +00:00