posix/mman: add mmap support for shm objects

Update #2859.

1 files changed, 165 insertions, 54 deletions

diff --git a/cpukit/posix/src/mmap.c b/cpukit/posix/src/mmap.c
index c05a65e078..9f555ade92 100644
--- a/cpukit/posix/src/mmap.c
+++ b/cpukit/posix/src/mmap.c
@@ -1,5 +1,10 @@
+/**
+ * @file
+ */
+
 /*
  * Copyright (c) 2012 Chris Johns (chrisj@rtems.org)
+ * Copyright (c) 2017 Gedare Bloom (gedare@rtems.org)
  *
  * The license and distribution terms for this file may be
  * found in the file LICENSE in this distribution or at
@@ -19,7 +24,8 @@
 
 #include "rtems/libio_.h"
 
-#include <rtems/posix/mmanimpl.h> 
+#include <rtems/posix/mmanimpl.h>
+#include <rtems/posix/shmimpl.h>
 
 #define RTEMS_MUTEX_ATTRIBS \
   (RTEMS_PRIORITY | RTEMS_SIMPLE_BINARY_SEMAPHORE | \
@@ -49,11 +55,14 @@ 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,
@@ -98,19 +107,45 @@ bool mmap_mappings_lock_release(
   return true;
 }
 
+/* Helper function only gets called for mmap mappings of shared memory objects
+ * with the MAP_SHARED flag.
+ */
+static void *shm_mmap( rtems_libio_t *iop, size_t len, int prot, off_t off)
+{
+  POSIX_Shm_Control *shm = iop_to_shm( iop );
+  void *m;
+
+  _Objects_Allocator_lock();
+
+  m = (*shm->shm_object.ops->object_mmap)( &shm->shm_object, len, prot, off);
+  if ( m != NULL ) {
+    /* Keep a reference in the shared memory to prevent its removal. */
+    ++shm->reference_count;
+
+    /* Update atime */
+    _POSIX_Shm_Update_atime(shm);
+  }
+
+  _Objects_Allocator_unlock();
+
+  return m;
+}
+
 void *mmap(
   void *addr, size_t len, int prot, int flags, int fildes, off_t off
 )
 {
-  struct stat   sb;
-  mmap_mapping* mapping;
-  ssize_t       r;
-  
-  /*
-   * Clear errno.
-   */
+  struct stat     sb;
+  mmap_mapping   *mapping;
+  ssize_t         r;
+  rtems_libio_t  *iop;
+  bool            map_fixed;
+
+  map_fixed = (flags & MAP_FIXED) == MAP_FIXED;
+
+  /* Clear errno. */
   errno = 0;
-  
+
   /*
    * Get a stat of the file to get the dev + inode number and to make sure the
    * fd is ok. The normal libio calls cannot be used because we need to return
@@ -122,109 +157,185 @@ void *mmap(
     return MAP_FAILED;
   }
 
+  /* fstat ensures we have a good file descriptor. Hold on to iop. */
+  iop = rtems_libio_iop( fildes );
+
   if ( len == 0 ) {
     errno = EINVAL;
     return MAP_FAILED;
   }
 
-  /*
-   * Check the type of file we have and make sure it is supported.
-   */
+  /* Check the type of file we have and make sure it is supported. */
   if ( S_ISDIR( sb.st_mode ) || S_ISLNK( sb.st_mode )) {
     errno = ENODEV;
     return MAP_FAILED;
   }
-  
+
   /*
    * We can provide read, write and execute because the memory in RTEMS does
    * not normally have protections but we cannot hide access to memory.
    */
   if ( prot == PROT_NONE ) {
+    errno = ENOTSUP;
+    return MAP_FAILED;
+  }
+
+  /* Either MAP_SHARED or MAP_PRIVATE must be defined, but not both */
+  if ( (flags & MAP_SHARED) == MAP_SHARED ) {
+    if ( (flags & MAP_PRIVATE) == MAP_PRIVATE ) {
+      errno = EINVAL;
+      return MAP_FAILED;
+    }
+  } else if ( (flags & MAP_PRIVATE != MAP_PRIVATE) ) {
     errno = EINVAL;
     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;
   }
 
   /*
-   * Obtain the mmap lock. Sets errno on failure.
+   * Check to see if the mapping is valid for other file/object types.
+   * Does this satisfy for devices?
    */
-  if ( !mmap_mappings_lock_obtain( ) )
+  if ( sb.st_size < off + len ) {
+    errno = ENXIO;
     return MAP_FAILED;
+  }
 
-  if (( flags & MAP_FIXED ) == MAP_FIXED ) {
-    rtems_chain_node* node = rtems_chain_first (&mmap_mappings);
-    while ( !rtems_chain_is_tail( &mmap_mappings, node )) {
-      /*
-       * If the map is fixed see if this address is already mapped. At this
-       * point in time if there is an overlap in the mappings we return an
-       * error.
-       */
-      mapping = (mmap_mapping*) node;
-      if ( ( addr >= mapping->addr ) &&
-           ( addr < ( mapping->addr + mapping->len )) ) {
-        mmap_mappings_lock_release( );
-        errno = ENXIO;
-        return MAP_FAILED;
-      }
-      node = rtems_chain_next( node );
+  /* 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 ) {
+      return MAP_FAILED;
     }
   }
 
+  /* Create the mapping */
   mapping = malloc( sizeof( mmap_mapping ));
   if ( !mapping ) {
-    mmap_mappings_lock_release( );
     errno = ENOMEM;
     return NULL;
   }
-
   memset( mapping, 0, sizeof( mmap_mapping ));
-
   mapping->len = len;
   mapping->flags = flags;
-  
-  if (( flags & MAP_FIXED ) != MAP_FIXED ) {
+  mapping->iop = iop;
+
+  /*
+   * HACK: We should have a better generic way to distinguish between
+   * shm objects and other mmap'd files. We need to know at munmap time
+   * if the mapping is to a shared memory object in order to refcnt shms.
+   * We could do this by providing mmap in the file operations if needed.
+   */
+  if ( S_ISREG( sb.st_mode ) || S_ISBLK( sb.st_mode ) ||
+       S_ISCHR( sb.st_mode ) || S_ISFIFO( sb.st_mode ) ||
+       S_ISSOCK( sb.st_mode ) ) {
+    mapping->is_shared_shm = false;
+  } else {
+    mapping->is_shared_shm = true;
+  }
+
+  /*
+   * MAP_SHARED currently is only supported for shared memory objects.
+   */
+  if ( (MAP_SHARED == (flags & MAP_SHARED)) && (mapping->is_shared_shm == false) ) {
+    free( mapping );
+    errno = ENOTSUP;
+    return MAP_FAILED;
+  }
+
+  if ( map_fixed ) {
+    mapping->addr = addr;
+  } else if ( MAP_PRIVATE == (flags & MAP_PRIVATE) ) {
+    /* private mappings of shared memory do not need special treatment. */
+    mapping->is_shared_shm = false;
     mapping->addr = malloc( len );
     if ( !mapping->addr ) {
-      mmap_mappings_lock_release( );
       free( mapping );
       errno = ENOMEM;
       return MAP_FAILED;
     }
+  }
 
-    /*
-     * Do not seek on character devices, pipes or sockets.
-     */
-    if ( S_ISREG( sb.st_mode ) || S_ISBLK( sb.st_mode ) ) {
-      if ( lseek( fildes, off, SEEK_SET ) < 0 ) {
-        mmap_mappings_lock_release( );
-        free( mapping->addr );
+  /* MAP_FIXED is not supported for shared memory objects with MAP_SHARED. */
+  if ( map_fixed && mapping->is_shared_shm ) {
+    free( mapping );
+    errno = ENOTSUP;
+    return MAP_FAILED;
+  }
+
+  /* Lock access to mmap_mappings. Sets errno on failure. */
+  if ( !mmap_mappings_lock_obtain( ) )
+    return MAP_FAILED;
+
+  if ( map_fixed ) {
+    rtems_chain_node* node = rtems_chain_first (&mmap_mappings);
+    while ( !rtems_chain_is_tail( &mmap_mappings, node )) {
+      /*
+       * If the map is fixed see if this address is already mapped. At this
+       * point in time if there is an overlap in the mappings we return an
+       * error. POSIX allows us to also return successfully by unmapping
+       * the overlapping prior mappings.
+       */
+      mapping = (mmap_mapping*) node;
+      if ( ( addr >= mapping->addr ) &&
+           ( addr < ( mapping->addr + mapping->len )) ) {
         free( mapping );
+        mmap_mappings_lock_release( );
+        errno = ENXIO;
         return MAP_FAILED;
       }
+      node = rtems_chain_next( node );
     }
   }
 
-  r = read( fildes, mapping->addr, len );
+  /* Populate the data */
+  if ( MAP_PRIVATE == (flags & MAP_PRIVATE) ) {
+    /*
+     * Use read() for private mappings. This updates atime as needed.
+     * Changes to the underlying object will NOT be reflected in the mapping.
+     * The underlying object can be removed while the mapping exists.
+     */
+    r = read( fildes, mapping->addr, len );
 
-  if ( r != len ) {
-    mmap_mappings_lock_release( );
-    free( mapping->addr );
-    free( mapping );
-    errno = ENXIO;
-    return MAP_FAILED;
+    if ( r != len ) {
+      mmap_mappings_lock_release( );
+      if ( !map_fixed ) {
+        free( mapping->addr );
+      }
+      free( mapping );
+      errno = ENXIO;
+      return MAP_FAILED;
+    }
+  } else if ( MAP_SHARED == (flags & MAP_SHARED) ) {
+    /* Currently only shm objects can be MAP_SHARED. */
+    mapping->addr = shm_mmap(iop, len, prot, off);
   }
 
+  /* 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_libio_increment_mapping_refcnt(iop);
+
   rtems_chain_append( &mmap_mappings, &mapping->node );
 
   mmap_mappings_lock_release( );
-  
+
   return mapping->addr;
 }