Account for temporary disk-space requirements on updates (ticket #175)

- When updating packages, we first create them with a temporary names
  and only after all files from payload have been created this way,
  the files are renamed to the final target. This means that performing
  an update temporarily requires roughly twice the disk space (and inodes)
  compared to the final result on per-package level. Which matters
  when space is tight, such as presumably in RhBug:872314.
- Simulate what happens on upgrades by adding block and inode delta
  to the equation: installing a file always consumes an inode and
  the specified amount of disk space. But when replacing files,
  reduce the size-delta from disk consumption *after* checking for
  problems in a given DSI.
- Also fixes inode accounting which has been broken for forever (since
  commit a9a1fd866c more exactly)

lib/transaction.c

@@ -55,6 +55,8 @@ struct diskspaceInfo_s {
     int64_t iavail;	/*!< No. of inodes available. */
     int64_t obneeded;	/*!< Bookkeeping to avoid duplicate reports */
     int64_t oineeded;	/*!< Bookkeeping to avoid duplicate reports */
+    int64_t bdelta;	/*!< Delta for temporary space need on updates */
+    int64_t idelta;	/*!< Delta for temporary inode need on updates */
 };
 
 /* Adjust for root only reserved space. On linux e2fs, this is 5%. */
@@ -210,7 +212,11 @@ static void rpmtsUpdateDSI(const rpmts ts, dev_t dev, const char *dirName,
      */
     case FA_CREATE:
 	dsi->bneeded += bneeded;
-	dsi->bneeded -= BLOCK_ROUND(prevSize, dsi->bsize);
+	dsi->ineeded++;
+	if (prevSize) {
+	    dsi->bdelta += BLOCK_ROUND(prevSize, dsi->bsize);
+	    dsi->idelta++;
+	}
 	break;
 
     case FA_ERASE:
@@ -254,6 +260,12 @@ static void rpmtsCheckDSIProblems(const rpmts ts, const rpmte te)
 		dsi->oineeded = dsi->ineeded;
 	    }
 	}
+
+	/* Adjust for temporary -> final disk consumption */
+	dsi->bneeded -= dsi->bdelta;
+	dsi->bdelta = 0;
+	dsi->ineeded -= dsi->idelta;
+	dsi->idelta = 0;
     }
 }