Make read/write of the f_offset field belonging to struct file MP-safe;

as part of the effort to unlock the kernel. Instead of relying on the
vnode lock, introduce a dedicated lock per file. Exclusive write access
is granted using the new foffset_enter and foffset_leave API. A
convenience function foffset_get is also available for threads that only
need to read the current offset.

The lock acquisition order in vn_write has been changed to match the one
in vn_read in order to avoid a potential deadlock. This change also gets
rid of a documented race in vn_read().

Inspired by the FreeBSD implementation.

With help and ok mpi@ visa@

0 files changed, 0 insertions, 0 deletions