'proc number' is process slot, 'endpoint' are generation-aware process

instance numbers, encoded and decoded using macros in <minix/endpoint.h>.

proc number -> endpoint migration
  . proc_nr in the interrupt hook is now an endpoint, proc_nr_e.
  . m_source for messages and notifies is now an endpoint, instead of
    proc number.
  . isokendpt() converts an endpoint to a process number, returns
    success (but fails if the process number is out of range, the
    process slot is not a living process, or the given endpoint
    number does not match the endpoint number in the process slot,
    indicating an old process).
  . okendpt() is the same as isokendpt(), but panic()s if the conversion
    fails. This is mainly used for decoding message.m_source endpoints,
    and other endpoint numbers in kernel data structures, which should
    always be correct.
  . if DEBUG_ENABLE_IPC_WARNINGS is enabled, isokendpt() and okendpt()
    get passed the __FILE__ and __LINE__ of the calling lines, and
    print messages about what is wrong with the endpoint number
    (out of range proc, empty proc, or inconsistent endpoint number),
    with the caller, making finding where the conversion failed easy
    without having to include code for every call to print where things
    went wrong. Sometimes this is harmless (wrong arg to a kernel call),
    sometimes it's a fatal internal inconsistency (bogus m_source).
  . some process table fields have been appended an _e to indicate it's
    become and endpoint.
  . process endpoint is stored in p_endpoint, without generation number.
    it turns out the kernel never needs the generation number, except
    when fork()ing, so it's decoded then.
  . kernel calls all take endpoints as arguments, not proc numbers.
    the one exception is sys_fork(), which needs to know in which slot
    to put the child.

kernel/system/do_vdevio.c

@@ -10,6 +10,7 @@
 
 #include "../system.h"
 #include <minix/devio.h>
+#include <minix/endpoint.h>
 
 #if USE_VDEVIO
 
@@ -34,7 +35,6 @@ register message *m_ptr;	/* pointer to request message */
   int vec_size;               /* size of vector */
   int io_in;                  /* true if input */
   size_t bytes;               /* # bytes to be copied */
-  int caller_proc;            /* process number of caller */
   vir_bytes caller_vir;       /* virtual address at caller */
   phys_bytes caller_phys;     /* physical address at caller */
   int i;
@@ -53,9 +53,8 @@ register message *m_ptr;	/* pointer to request message */
   if (bytes > sizeof(vdevio_buf))  return(E2BIG);
 
   /* Calculate physical addresses and copy (port,value)-pairs from user. */
-  caller_proc = m_ptr->m_source; 
   caller_vir = (vir_bytes) m_ptr->DIO_VEC_ADDR;
-  caller_phys = umap_local(proc_addr(caller_proc), D, caller_vir, bytes);
+  caller_phys = umap_local(proc_addr(who_p), D, caller_vir, bytes);
   if (0 == caller_phys) return(EFAULT);
   phys_copy(caller_phys, vir2phys(vdevio_buf), (phys_bytes) bytes);