From 49532259e5e915ee294bc2d7f966615ab26ceed3 Mon Sep 17 00:00:00 2001
From: Ben Gras <ben@minix3.org>
Date: Wed, 21 Sep 2011 17:52:45 +0000
Subject: [PATCH] mfs: improve & simplify secondary cache logic

	. fixes "!" errors when booting from cd
---
 servers/mfs/cache.c | 31 ++++++++++++++-----------------
 servers/mfs/read.c  |  2 +-
 2 files changed, 15 insertions(+), 18 deletions(-)

diff --git a/servers/mfs/cache.c b/servers/mfs/cache.c
index 96715f6c5..49a82ebdd 100644
--- a/servers/mfs/cache.c
+++ b/servers/mfs/cache.c
@@ -28,7 +28,7 @@
 FORWARD _PROTOTYPE( void rm_lru, (struct buf *bp) );
 FORWARD _PROTOTYPE( void rw_block, (struct buf *, int) );
 
-PRIVATE int vmcache_avail = -1; /* 0 if not available, >0 if available. */
+PRIVATE int vmcache = 0; /* are we using vm's secondary cache? (initially not) */
 
 /*===========================================================================*
  *				get_block				     *
@@ -57,27 +57,11 @@ PUBLIC struct buf *get_block(
   int b;
   static struct buf *bp, *prev_ptr;
   u64_t yieldid = VM_BLOCKID_NONE, getid = make64(dev, block);
-  int vmcache = 0;
 
   assert(buf_hash);
   assert(buf);
   assert(nr_bufs > 0);
 
-  if(vmcache_avail < 0) {
-	/* Test once for the availability of the vm yield block feature. */
-	if(vm_forgetblock(VM_BLOCKID_NONE) == ENOSYS) {
-		vmcache_avail = 0;
-	} else {
-		vmcache_avail = 1;
-	}
-  }
-
-  /* use vmcache if it's available, and allowed, and we're not doing
-   * i/o on a ram disk device.
-   */
-  if(vmcache_avail && may_use_vmcache && major(dev) != MEMORY_MAJOR)
-	vmcache = 1;
-
   ASSERT(fs_block_size > 0);
 
   /* Search the hash chain for (dev, block). Do_read() can use 
@@ -586,6 +570,19 @@ PUBLIC void set_blocksize(struct super_block *sp)
   cache_resize(sp->s_block_size, MINBUFS);
   bufs = bufs_heuristic(sp);
   cache_resize(sp->s_block_size, bufs);
+  
+  /* Decide whether to use seconday cache or not.
+   * Only do this if
+   *	- it's available, and
+   *	- use of it hasn't been disabled for this fs, and
+   *	- our main FS device isn't a memory device
+   */
+
+  vmcache = 0;
+  if(vm_forgetblock(VM_BLOCKID_NONE) != ENOSYS &&
+  	may_use_vmcache && major(sp->s_dev) != MEMORY_MAJOR) {
+	vmcache = 1;
+  }
 }
 
 /*===========================================================================*
diff --git a/servers/mfs/read.c b/servers/mfs/read.c
index ae1a22367..abf0af653 100644
--- a/servers/mfs/read.c
+++ b/servers/mfs/read.c
@@ -412,7 +412,7 @@ PUBLIC void read_ahead()
   rdahed_inode = NULL;	/* turn off read ahead */
   if ( (b = read_map(rip, rdahedpos)) == NO_BLOCK) return;	/* at EOF */
 
-  assert(rdahedpos > 0); /* So we can safely cast it to unsigned below */
+  assert(rdahedpos >= 0); /* So we can safely cast it to unsigned below */
 
   bp = rahead(rip, b, cvul64( (unsigned long) rdahedpos), block_size);
   put_block(bp, PARTIAL_DATA_BLOCK);
-- 
2.44.0