1 files changed, 111 insertions, 0 deletions
diff --git a/src/mongo/db/storage/extent.h b/src/mongo/db/storage/extent.h
new file mode 100644
index 00000000000..3553726234b
--- /dev/null
+++ b/src/mongo/db/storage/extent.h
@@ -0,0 +1,111 @@
+// extent.h
+
+/**
+*    Copyright (C) 2013 10gen Inc.
+*
+*    This program is free software: you can redistribute it and/or  modify
+*    it under the terms of the GNU Affero General Public License, version 3,
+*    as published by the Free Software Foundation.
+*
+*    This program is distributed in the hope that it will be useful,
+*    but WITHOUT ANY WARRANTY; without even the implied warranty of
+*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*    GNU Affero General Public License for more details.
+*
+*    You should have received a copy of the GNU Affero General Public License
+*    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#pragma once
+
+#include "mongo/db/diskloc.h"
+#include "mongo/db/storage/namespace.h"
+
+namespace mongo {
+
+    /* extents are datafile regions where all the records within the region
+       belong to the same namespace.
+
+    (11:12:35 AM) dm10gen: when the extent is allocated, all its empty space is stuck into one big DeletedRecord
+    (11:12:55 AM) dm10gen: and that is placed on the free list
+    */
+#pragma pack(1)
+    class Extent {
+    public:
+        enum { extentSignature = 0x41424344 };
+        unsigned magic;
+        DiskLoc myLoc;
+        DiskLoc xnext, xprev; /* next/prev extent for this namespace */
+
+        /* which namespace this extent is for.  this is just for troubleshooting really
+           and won't even be correct if the collection were renamed!
+        */
+        Namespace nsDiagnostic;
+
+        int length;   /* size of the extent, including these fields */
+        DiskLoc firstRecord;
+        DiskLoc lastRecord;
+        char _extentData[4];
+
+        static int HeaderSize() { return sizeof(Extent)-4; }
+
+        bool validates(const DiskLoc diskLoc, BSONArrayBuilder* errors = NULL);
+
+        BSONObj dump();
+
+        void dump(iostream& s);
+
+        /* assumes already zeroed -- insufficient for block 'reuse' perhaps
+        Returns a DeletedRecord location which is the data in the extent ready for us.
+        Caller will need to add that to the freelist structure in namespacedetail.
+        */
+        DiskLoc init(const char *nsname, int _length, int _fileNo, int _offset, bool capped);
+
+        /* like init(), but for a reuse case */
+        DiskLoc reuse(const char *nsname, bool newUseIsAsCapped);
+
+        bool isOk() const { return magic == extentSignature; }
+        void assertOk() const { verify(isOk()); }
+
+        Record* getRecord(DiskLoc dl) {
+            verify( !dl.isNull() );
+            verify( dl.sameFile(myLoc) );
+            int x = dl.getOfs() - myLoc.getOfs();
+            verify( x > 0 );
+            return (Record *) (((char *) this) + x);
+        }
+
+        Extent* getNextExtent();
+        Extent* getPrevExtent();
+
+        static int maxSize();
+        static int minSize() { return 0x1000; }
+        /**
+         * @param len lengt of record we need
+         * @param lastRecord size of last extent which is a factor in next extent size
+         */
+        static int followupSize(int len, int lastExtentLen);
+
+        /** get a suggested size for the first extent in a namespace
+         *  @param len length of record we need to insert
+         */
+        static int initialSize(int len);
+
+        struct FL {
+            DiskLoc firstRecord;
+            DiskLoc lastRecord;
+        };
+        /** often we want to update just the firstRecord and lastRecord fields.
+            this helper is for that -- for use with getDur().writing() method
+        */
+        FL* fl() { return (FL*) &firstRecord; }
+
+        /** caller must declare write intent first */
+        void markEmpty();
+    private:
+        DiskLoc _reuse(const char *nsname, bool newUseIsAsCapped); // recycle an extent and reuse it for a different ns
+    };
+
+#pragma pack()
+
+}