[PATCH 4/6] posix/mman: add mmap support for shm objects

[Gedare Bloom]

Update #2859.
---
 cpukit/posix/include/rtems/posix/mmanimpl.h |  4 ++-
 cpukit/posix/src/mmap.c                     | 43 +++++++++++++++++++++++++++--
 2 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/cpukit/posix/include/rtems/posix/mmanimpl.h b/cpukit/posix/include/rtems/posix/mmanimpl.h
index 9743685..78bda53 100644
--- a/cpukit/posix/include/rtems/posix/mmanimpl.h
+++ b/cpukit/posix/include/rtems/posix/mmanimpl.h
@@ -16,12 +16,14 @@
 #ifndef _RTEMS_POSIX_MMANIMPL_H
 #define _RTEMS_POSIX_MMANIMPL_H
 
-#include <rtems/chain.h>
+#include <rtems/chain.h> /* FIXME: use score chains for proper layering? */
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+/* FIXME: add Doxygen */
+
 /**
  * Every mmap'ed region has a mapping.
  */
diff --git a/cpukit/posix/src/mmap.c b/cpukit/posix/src/mmap.c
index c05a65e..3c5f81e 100644
--- a/cpukit/posix/src/mmap.c
+++ b/cpukit/posix/src/mmap.c
@@ -1,5 +1,10 @@
+/**
+ * @file
+ */
+
 /*
  * Copyright (c) 2012 Chris Johns (chrisj at rtems.org)
+ * Copyright (c) 2017 Gedare Bloom (gedare at rtems.org)
  *
  * The license and distribution terms for this file may be
  * found in the file LICENSE in this distribution or at
@@ -49,11 +54,14 @@ bool mmap_mappings_lock_create(
    * the libio lock is locked and we then test the mapping lock again. If not
    * present we create the mapping lock then release libio lock.
    */
+  /* FIXME: double-checked locking anti-pattern. */
   if ( mmap_mappings_lock == 0 ) {
     rtems_status_code sc = RTEMS_SUCCESSFUL;
     rtems_chain_initialize_empty( &mmap_mappings );
     rtems_semaphore_obtain( rtems_libio_semaphore,
                             RTEMS_WAIT, RTEMS_NO_TIMEOUT );
+    /* FIXME: account for semaphore in confdefs, or maybe just use the
+     * rtems_libio_semaphore? */
     if ( mmap_mappings_lock == 0 )
       sc = rtems_semaphore_create( rtems_build_name( 'M', 'M', 'A', 'P' ),
                                    1,
@@ -140,20 +148,40 @@ void *mmap(
    * not normally have protections but we cannot hide access to memory.
    */
   if ( prot == PROT_NONE ) {
-    errno = EINVAL;
+    errno = ENOTSUP;
     return MAP_FAILED;
   }
   
   /*
-   * Check to see if the mapping is valid for the file.
+   * We can not normally provide restriction of write access. Reject any
+   * attempt to map without write permission, since we are not able to
+   * prevent a write from succeeding.
+   */
+  if ( PROT_WRITE != (prot & PROT_WRITE) ) {
+    errno = ENOTSUP;
+    return MAP_FAILED;
+  }
+
+  /*
+   * Check to see if the mapping is valid for a regular file.
    */
   if ( S_ISREG( sb.st_mode )
+  /* FIXME: Should this be using strict inequality comparisons? It would
+   * be valid to map a region exactly equal to the st_size, e.g. see below. */
        && (( off >= sb.st_size ) || (( off + len ) >= sb.st_size ))) {
     errno = EOVERFLOW;
     return MAP_FAILED;
   }
 
   /*
+   * Check to see if the mapping is valid for other file/object types.
+   */
+  if ( sb.st_size < off + len ) {
+    errno = ENXIO;
+    return MAP_FAILED;
+  }
+
+  /*
    * Obtain the mmap lock. Sets errno on failure.
    */
   if ( !mmap_mappings_lock_obtain( ) )
@@ -200,7 +228,7 @@ void *mmap(
     }
 
     /*
-     * Do not seek on character devices, pipes or sockets.
+     * Do not seek on character devices, pipes, sockets, or memory objects.
      */
     if ( S_ISREG( sb.st_mode ) || S_ISBLK( sb.st_mode ) ) {
       if ( lseek( fildes, off, SEEK_SET ) < 0 ) {
@@ -212,6 +240,7 @@ void *mmap(
     }
   }
 
+  /* read updates atime satisfying POSIX spec for mmap */
   r = read( fildes, mapping->addr, len );
 
   if ( r != len ) {
@@ -222,6 +251,14 @@ void *mmap(
     return MAP_FAILED;
   }
 
+  /* FIXME: for a mapping with MAP_SHARED and PROT_WRITE the mtime/ctime
+   * should be updated when there is a write reference to the mapped region.
+   * How do we make this happen? */
+
+  /* FIXME: add an extra reference to the file associated with fildes that
+   * is not removed by a subsequent close().  This reference shall be removed
+   * when there are no more mappings to the file. */
+
   rtems_chain_append( &mmap_mappings, &mapping->node );
 
   mmap_mappings_lock_release( );
-- 
2.7.4