Bug#195018: [patch] make DynamicMMap dynamic

[Michael Vogt <mvogt@acm.org>]

Hi,

I would like to ask for opinions/review of the attached patch that
makes dynamic mmap really dynamic and grow the buffer dynamically.

It also changes the non-file backed operation mode to use anonymous
mmap instead of new char[]. 

You can test it with, e.g.:
$ sudo rm /var/cache/apt/*.bin
$ apt-cache -o APT::Cache-Limit=10000 search foo
$ sudo apt-cache -o  APT::Cache-Limit=10000 search foo

this will not work without the patch but it should with it.



Cheers,
 Michael

=== modified file 'apt-pkg/contrib/mmap.cc'
--- apt-pkg/contrib/mmap.cc	2006-03-12 20:18:45 +0000
+++ apt-pkg/contrib/mmap.cc	2007-04-27 13:40:13 +0000
@@ -175,9 +175,8 @@
    if (_error->PendingError() == true)
       return;
    
-   Base = new unsigned char[WorkSpace];
-   memset(Base,0,WorkSpace);
-   iSize = 0;
+   // use anonymous mmap() to get the memory
+   Base = mmap(0, WorkSpace, PROT_READ|PROT_WRITE, MAP_ANON|MAP_PRIVATE, -1, 0);
 }
 									/*}}}*/
 // DynamicMMap::~DynamicMMap - Destructor				/*{{{*/
@@ -187,7 +186,7 @@
 {
    if (Fd == 0)
    {
-      delete [] (unsigned char *)Base;
+      munmap(Base, WorkSpace);
       return;
    }
    
@@ -211,8 +210,15 @@
    // Just in case error check
    if (Result + Size > WorkSpace)
    {
-      _error->Error("Dynamic MMap ran out of room");
-      return 0;
+      // try to grow the buffer
+      while(Result + Size > WorkSpace)
+      {
+	 if(!Grow())
+	 {
+	    _error->Error("Dynamic MMap ran out of room");
+	    return 0;
+	 }
+      }
    }
 
    return Result;
@@ -273,8 +279,15 @@
    // Just in case error check
    if (Result + Len > WorkSpace)
    {
-      _error->Error("Dynamic MMap ran out of room");
-      return 0;
+      // try to grow the buffer
+      while(Result + Len > WorkSpace)
+      {
+	 if(!Grow())
+	 {
+	    _error->Error("Dynamic MMap ran out of room");
+	    return 0;
+	 }
+      }
    }   
    
    if (Len == (unsigned long)-1)
@@ -285,3 +298,24 @@
    return Result;
 }
 									/*}}}*/
+// DynamicMMap::Grow - Grow the mmap    	                        /*{{{*/
+// ---------------------------------------------------------------------
+bool DynamicMMap::Grow()
+{
+   unsigned long newSize = WorkSpace * 2;
+
+   if(Fd != 0) 
+   {
+      Fd->Seek(newSize - 1);
+      char C = 0;
+      Fd->Write(&C,sizeof(C));
+   }
+   void *newBase = mremap(Base, WorkSpace, newSize, 0);
+   if(newBase == MAP_FAILED) 
+      return false;
+
+   WorkSpace = newSize;
+   return true;
+}
+
+									/*}}}*/

=== modified file 'apt-pkg/contrib/mmap.h'
--- apt-pkg/contrib/mmap.h	2006-03-12 20:18:45 +0000
+++ apt-pkg/contrib/mmap.h	2007-04-26 09:11:14 +0000
@@ -87,6 +87,8 @@
    unsigned long WorkSpace;
    Pool *Pools;
    unsigned int PoolCount;
+
+   bool Grow();
    
    public: