posix/mman: add mmap support for shm objects

Update #2859.

3 files changed, 72 insertions, 2 deletions

diff --git a/cpukit/libcsupport/include/rtems/libio.h b/cpukit/libcsupport/include/rtems/libio.h
index a87031ca91..d0824b4e85 100644
--- a/cpukit/libcsupport/include/rtems/libio.h
+++ b/cpukit/libcsupport/include/rtems/libio.h
@@ -1282,6 +1282,7 @@ struct rtems_libio_tt {
   rtems_driver_name_t                    *driver;
   off_t                                   offset;    /* current offset into file */
   uint32_t                                flags;
+  uint32_t                                mapping_refcnt; /* current mappings */
   rtems_filesystem_location_info_t        pathinfo;
   uint32_t                                data0;     /* private to "driver" */
   void                                   *data1;     /* ... */
diff --git a/cpukit/libcsupport/include/rtems/libio_.h b/cpukit/libcsupport/include/rtems/libio_.h
index c2fb975bf7..695a4c45a5 100644
--- a/cpukit/libcsupport/include/rtems/libio_.h
+++ b/cpukit/libcsupport/include/rtems/libio_.h
@@ -304,6 +304,47 @@ void rtems_libio_free(
   rtems_libio_t *iop
 );
 
+/**
+ * Garbage collects the free libio in case it was previously freed but there
+ * were still references to it.
+ */
+void rtems_libio_check_deferred_free( rtems_libio_t *iop );
+
+/**
+ * Increment the reference count tracking number of mmap mappings of a file.
+ * Returns the updated reference count value.
+ */
+static inline uint32_t rtems_libio_increment_mapping_refcnt(rtems_libio_t *iop)
+{
+  uint32_t refcnt;
+  rtems_libio_lock();
+  refcnt = ++iop->mapping_refcnt;
+  rtems_libio_unlock();
+  return refcnt;
+}
+
+/**
+ * Decrement the reference count tracking number of mmap mappings of a file.
+ * Returns the updated reference count value.
+ */
+static inline uint32_t rtems_libio_decrement_mapping_refcnt(rtems_libio_t *iop)
+{
+  uint32_t refcnt;
+  rtems_libio_lock();
+  refcnt = --iop->mapping_refcnt;
+  rtems_libio_unlock();
+  return refcnt;
+}
+
+static inline bool rtems_libio_is_mapped(rtems_libio_t *iop)
+{
+  bool is_mapped;
+  rtems_libio_lock();
+  is_mapped = iop->mapping_refcnt != 0;
+  rtems_libio_unlock();
+  return is_mapped;
+}
+
 /*
  *  File System Routine Prototypes
  */
diff --git a/cpukit/libcsupport/src/libio.c b/cpukit/libcsupport/src/libio.c
index 22be6411a2..e89634f090 100644
--- a/cpukit/libcsupport/src/libio.c
+++ b/cpukit/libcsupport/src/libio.c
@@ -138,8 +138,36 @@ void rtems_libio_free(
   rtems_libio_lock();
 
     iop->flags = 0;
-    iop->data1 = rtems_libio_iop_freelist;
-    rtems_libio_iop_freelist = iop;
+    /* If the mapping_refcnt is non-zero, the deferred free will be
+     * called by munmap. The iop is no longer good to use, but it cannot
+     * be recycled until the mapped file is unmapped. deferred free knows
+     * it can recycle the iop in case flags == 0 and iop->data1 == iop,
+     * since these two conditions are not otherwise satisifed at
+     * the same time. It may be possible that iop->data1 == iop when
+     * flags != 0 because data1 is private to the driver. However, flags == 0
+     * means a freed iop, and an iop on the freelist cannot store a pointer
+     * to itself in data1, or else the freelist is corrupted. We can't use
+     * NULL in data1 as an indicator because it is used by the tail of the
+     * freelist. */
+    if ( iop->mapping_refcnt == 0 ) {
+      iop->data1 = rtems_libio_iop_freelist;
+      rtems_libio_iop_freelist = iop;
+    } else {
+      iop->data1 = iop;
+    }
 
   rtems_libio_unlock();
 }
+
+void rtems_libio_check_deferred_free(
+  rtems_libio_t *iop
+)
+{
+  rtems_libio_lock();
+    if ( iop->mapping_refcnt == 0 && iop->flags == 0 && iop->data1 == iop) {
+      /* No mappings and rtems_libio_free already called, recycle the iop */
+      iop->data1 = rtems_libio_iop_freelist;
+      rtems_libio_iop_freelist = iop;
+    }
+  rtems_libio_unlock();
+}