vfs_get_vnode_cache() now only allocates a new cache if requested: this

prevents the system to allocate caches for files that don't use or have
a file cache (ie. only those can be mmap()ed!).
Therefore, cache_prefetch() no longer crashes when trying to prefetch
files without a file cache.
read_into_cache() no longer does anything if the requested size is 0.
Fixed a bug in cache_prefetch_vnode(): if the cache couldn't be retrieved,
it put the vnode, but didn't own it (the caller does).


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@13904 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/vfs.h

@@ -75,7 +75,7 @@ status_t vfs_get_cookie_from_fd(int fd, void **_cookie);
 bool vfs_can_page(void *vnode, void *cookie);
 status_t vfs_read_pages(void *vnode, void *cookie, off_t pos, const iovec *vecs, size_t count, size_t *_numBytes);
 status_t vfs_write_pages(void *vnode, void *cookie, off_t pos, const iovec *vecs, size_t count, size_t *_numBytes);
-status_t vfs_get_vnode_cache(void *vnode, struct vm_cache_ref **_cache);
+status_t vfs_get_vnode_cache(void *vnode, struct vm_cache_ref **_cache, bool allocate);
 status_t vfs_get_file_map( void *_vnode, off_t offset, size_t size, struct file_io_vec *vecs, size_t *_count);
 status_t vfs_get_fs_node_from_path(mount_id mountID, const char *path, bool kernel, void **_node);
 status_t vfs_stat_vnode(void *_vnode, struct stat *stat);

src/system/kernel/cache/file_cache.cpp

@@ -487,6 +487,10 @@ read_into_cache(file_cache_ref *ref, off_t offset, size_t size, addr_t buffer, s
 	TRACE(("read_from_cache: ref = %p, offset = %Ld, size = %lu, buffer = %p, bufferSize = %lu\n",
 		ref, offset, size, (void *)buffer, bufferSize));
 
+	// do we have to read in anything at all?
+	if (size == 0)
+		return B_OK;
+
 	// make sure "offset" is page aligned - but also remember the page offset
 	int32 pageOffset = offset & (B_PAGE_SIZE - 1);
 	size = PAGE_ALIGN(size + pageOffset);
@@ -497,7 +501,8 @@ read_into_cache(file_cache_ref *ref, off_t offset, size_t size, addr_t buffer, s
 		if (chunkSize > (MAX_IO_VECS * B_PAGE_SIZE))
 			chunkSize = MAX_IO_VECS * B_PAGE_SIZE;
 
-		status_t status = read_chunk_into_cache(ref, offset, chunkSize, pageOffset, buffer, bufferSize);
+		status_t status = read_chunk_into_cache(ref, offset, chunkSize, pageOffset,
+								buffer, bufferSize);
 		if (status != B_OK)
 			return status;
 
@@ -819,10 +824,8 @@ extern "C" void
 cache_prefetch_vnode(void *vnode, off_t offset, size_t size)
 {
 	vm_cache_ref *cache;
-	if (vfs_get_vnode_cache(vnode, &cache) != B_OK) {
-		vfs_put_vnode(vnode);
+	if (vfs_get_vnode_cache(vnode, &cache, false) != B_OK)
 		return;
-	}
 
 	file_cache_ref *ref = (struct file_cache_ref *)((vnode_store *)cache->cache->store)->file_cache_ref;
 	off_t fileSize = cache->cache->virtual_size;
@@ -985,7 +988,7 @@ file_cache_create(mount_id mountID, vnode_id vnodeID, off_t size, int fd)
 	if (vfs_lookup_vnode(mountID, vnodeID, &ref->vnode) != B_OK)
 		goto err2;
 
-	if (vfs_get_vnode_cache(ref->vnode, &ref->cache) != B_OK)
+	if (vfs_get_vnode_cache(ref->vnode, &ref->cache, true) != B_OK)
 		goto err3;
 
 	ref->cache->cache->virtual_size = size;

src/system/kernel/fs/vfs.cpp

@@ -2458,7 +2458,7 @@ vfs_write_pages(void *_vnode, void *cookie, off_t pos, const iovec *vecs, size_t
 
 
 extern "C" status_t
-vfs_get_vnode_cache(void *_vnode, vm_cache_ref **_cache)
+vfs_get_vnode_cache(void *_vnode, vm_cache_ref **_cache, bool allocate)
 {
 	struct vnode *vnode = (struct vnode *)_vnode;
 
@@ -2470,9 +2470,14 @@ vfs_get_vnode_cache(void *_vnode, vm_cache_ref **_cache)
 	mutex_lock(&sVnodeMutex);
 
 	status_t status = B_OK;
+
 	// The cache could have been created in the meantime
-	if (vnode->cache == NULL)
-		status = vm_create_vnode_cache(vnode, &vnode->cache);
+	if (vnode->cache == NULL) {
+		if (allocate)
+			status = vm_create_vnode_cache(vnode, &vnode->cache);
+		else
+			status = B_BAD_VALUE;
+	}
 
 	if (status == B_OK)
 		*_cache = vnode->cache;

src/system/kernel/vm/vm.cpp

@@ -1099,7 +1099,7 @@ _vm_map_file(aspace_id aid, const char *name, void **_address, uint32 addressSpe
 	if (status < B_OK)
 		goto err1;
 
-	status = vfs_get_vnode_cache(vnode, &cacheRef);
+	status = vfs_get_vnode_cache(vnode, &cacheRef, false);
 	if (status < B_OK)
 		goto err2;