userlandfs: Fix file_cache_read

* Prevent the userlandfs server from calling clone_area on an area
  that might have already been deleted.
* _HandleRequest(FileCacheReadRequest*) waits for a reply from the
  server when bytesRead > 0.  This ensures that the server has time to
  use the area holding the returned data, before that area is deleted
  when the RequestAllocator goes out of scope in the kernel add-on.
  However, if bytesRead is 0, the server will still call clone_area,
  even though by that time the area has probably been deleted.  This
  leads to a B_BAD_VALUE error when the FS tries to use the emulated
  file_cache_read at the end of a file, which differs from the
  normal behavior of file_cache_read.
* _HandleRequest(ReadFromIORequestRequest*) has similar logic in that
  it waits for a server reply, but not if size == 0.  It's possible
  that a similar problem could occur here. This test can be
  dropped if no requests with size 0 are ever sent from the server to
  begin with.
* For other _HandleRequest overrides, the kernel never waits for a
  server reply, and this causes no problems.  This could be because the
  size of data returned fits in the port buffer, so no external area
  needs to be created by RequestAllocator::AllocateAddress.

Change-Id: If070901c25d446e00e67a74a7883808d8a38dae2
Reviewed-on: https://review.haiku-os.org/c/haiku/+/8721
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

src/add-ons/kernel/file_systems/userlandfs/kernel_add_on/KernelRequestHandler.cpp

@@ -803,7 +803,7 @@ KernelRequestHandler::_HandleRequest(ReadFromIORequestRequest* request)
 	reply->error = result;
 
 	// send the reply
-	if (reply->error == B_OK && size > 0) {
+	if (reply->error == B_OK) {
 		SingleReplyRequestHandler handler(RECEIPT_ACK_REPLY);
 		return fPort->SendRequest(&allocator, &handler);
 	}

src/add-ons/kernel/file_systems/userlandfs/private/Requests.cpp

@@ -5,12 +5,12 @@
 #include "Debug.h"
 #include "Requests.h"
 
-#define _ADD_ADDRESS(_address, _flags)				\
+#define _ADD_ADDRESS(_address, _flags) {			\
 	if (*count >= MAX_REQUEST_ADDRESS_COUNT)		\
 		return B_BAD_VALUE;							\
 	infos[*count].address = &_address;				\
 	infos[*count].flags = _flags;					\
-	infos[(*count)++].max_size = INT32_MAX;	// TODO:...
+	infos[(*count)++].max_size = INT32_MAX;	} // TODO:...
 
 #define ADD_ADDRESS(address)	_ADD_ADDRESS(address, 0)
 #define ADD_STRING(address)		_ADD_ADDRESS(address, ADDRESS_IS_STRING)
@@ -309,7 +309,8 @@ NotifyQueryRequest::GetAddressInfos(AddressInfo* infos, int32* count)
 status_t
 FileCacheReadReply::GetAddressInfos(AddressInfo* infos, int32* count)
 {
-	ADD_ADDRESS(buffer);
+	if (bytesRead > 0)
+		ADD_ADDRESS(buffer);
 	return B_OK;
 }
 

src/add-ons/kernel/file_systems/userlandfs/server/fuse/FUSEVolume.cpp

@@ -1022,6 +1022,9 @@ FUSEVolume::DoIO(void* _node, void* _cookie, const IORequestInfo& requestInfo)
 	FUSENode* node = (FUSENode*)_node;
 	FileCookie* cookie = (FileCookie*)_cookie;
 
+	if (requestInfo.length == 0)
+		return B_OK;
+
 	NodeReadLocker nodeLocker(this, node, true);
 	if (nodeLocker.Status() != B_OK)
 		RETURN_ERROR(nodeLocker.Status());

src/add-ons/kernel/file_systems/userlandfs/server/haiku/haiku_kernel_emu.cpp

@@ -384,6 +384,9 @@ io_request_length(const io_request* request)
 status_t
 read_from_io_request(io_request* _request, void* buffer, size_t size)
 {
+	if (size == 0)
+		return B_OK;
+
 	HaikuKernelIORequest* request = (HaikuKernelIORequest*)_request;
 
 	// send the request