block_mmap_Alloc: commoditize block allocation from mmap

Only the file access uses this, but I don't like "wild" callbacks into plugins.

include/vlc_block.h

@@ -148,6 +148,18 @@ static inline void block_Release( block_t *p_block )
     p_block->pf_release( p_block );
 }
 
+/**
+ * Creates a block from a virtual address memory mapping (mmap).
+ * This is provided by LibVLC so that mmap blocks can safely be deallocated
+ * even after the allocating plugin has been unloaded from memory.
+ *
+ * @param addr base address of the mapping (as returned by mmap)
+ * @param length length (bytes) of the mapping (as passed to mmap)
+ * @return NULL if addr is MAP_FAILED, or an error occurred (in the later
+ * case, munmap(addr, length) is invoked before returning).
+ */
+VLC_EXPORT( block_t *, block_mmap_Alloc, (void *addr, size_t length) );
+
 /****************************************************************************
  * Chains of blocks functions helper
  ****************************************************************************

modules/access/file.c

@@ -345,23 +345,6 @@ static ssize_t Read( access_t *p_access, uint8_t *p_buffer, size_t i_len )
 #ifdef HAVE_MMAP
 # define MMAP_SIZE (1 << 20)
 
-struct block_sys_t
-{
-    block_t self;
-    //vlc_object_t *owner;
-    void *base_addr;
-    size_t length;
-};
-
-static void mmapRelease (block_t *block)
-{
-    block_sys_t *p_sys = (block_sys_t *)block;
-
-    munmap (p_sys->base_addr, p_sys->length);
-    //vlc_object_release (p_sys->owner);
-    free (p_sys);
-}
-
 static block_t *mmapBlock (access_t *p_access)
 {
     access_sys_t *p_sys = p_access->p_sys;
@@ -420,36 +403,31 @@ static block_t *mmapBlock (access_t *p_access)
     }
 
     p_access->info.i_pos = offset + length;
-    msg_Dbg (p_access, "mapped 0x%lx bytes at %p from offset 0x%lx",
-             (unsigned long)length, addr, (unsigned long)offset);
 
-    block_sys_t *block = malloc (sizeof (*block));
+    block_t *block = block_mmap_Alloc (addr, length);
     if (block == NULL)
-    {
-        munmap (addr, length);
         return NULL;
-    }
 
-    block_Init (&block->self, ((uint8_t *)addr) + align, length - align);
-    block->self.pf_release = mmapRelease;
-    block->base_addr = addr;
-    block->length = length;
-    //vlc_object_yield (block->owner = VLC_OBJECT (p_access));
+    block->p_buffer += align;
+    block->i_buffer -= align;
 
 #ifndef NDEBUG
+    msg_Dbg (p_access, "mapped 0x%lx bytes at %p from offset 0x%lx",
+             (unsigned long)length, addr, (unsigned long)offset);
+
     /* Compare normal I/O with memory mapping */
-    char *buf = malloc (block->self.i_buffer);
-    ssize_t i_read = read (p_sys->fd, buf, block->self.i_buffer);
+    char *buf = malloc (block->i_buffer);
+    ssize_t i_read = read (p_sys->fd, buf, block->i_buffer);
 
-    if (i_read != (ssize_t)block->self.i_buffer)
+    if (i_read != (ssize_t)block->i_buffer)
         msg_Err (p_access, "read %u instead of %u bytes", (unsigned)i_read,
-                 (unsigned)block->self.i_buffer);
-    if (memcmp (buf, block->self.p_buffer, block->self.i_buffer))
+                 (unsigned)block->i_buffer);
+    if (memcmp (buf, block->p_buffer, block->i_buffer))
         msg_Err (p_access, "inconsistent data buffer");
     free (buf);
 #endif
 
-    return &block->self;
+    return block;
 }
 #endif
 

src/libvlc.sym

@@ -42,6 +42,7 @@ block_FifoShow
 block_FifoSize
 block_FifoWake
 block_Init
+block_mmap_Alloc
 block_Realloc
 config_ChainCreate
 config_ChainDestroy

src/misc/block.c

@@ -155,6 +155,44 @@ block_t *block_Realloc( block_t *p_block, ssize_t i_prebody, size_t i_body )
     return p_block;
 }
 
+#ifdef HAVE_MMAP
+# include <sys/mman.h>
+
+typedef struct block_mmap_t
+{
+    block_t     self;
+    void       *base_addr;
+    size_t      length;
+} block_mmap_t;
+
+static void block_mmap_Release (block_t *block)
+{
+    block_mmap_t *p_sys = (block_mmap_t *)block;
+
+    munmap (p_sys->base_addr, p_sys->length);
+    free (p_sys);
+}
+
+block_t *block_mmap_Alloc (void *addr, size_t length)
+{
+    if (addr == MAP_FAILED)
+        return NULL;
+
+    block_mmap_t *block = malloc (sizeof (*block));
+    if (block == NULL)
+    {
+        munmap (addr, length);
+        return NULL;
+    }
+
+    block_Init (&block->self, (uint8_t *)addr, length);
+    block->self.pf_release = block_mmap_Release;
+    block->base_addr = addr;
+    block->length = length;
+    return &block->self;
+}
+#endif
+
 /*****************************************************************************
  * block_fifo_t management
  *****************************************************************************/