ANDROID: fuse: Adjust Passthrough for writeback cache

This adjusts some tracking to allow passthrough and writeback cache to
co-exist with eachother

Change-Id: I5b8b3940a8c096cd3598d7c188439c6c636c01a1
Bug: 372951405
Fixes: 3ae410445f ("ANDROID: fuse: Allow passthrough and not passthrough")
test: atest android.scopedstorage.cts.general.ScopedStorageDeviceTest
Signed-off-by: Daniel Rosenberg <drosen@google.com>

fs/fuse/file.c

@@ -3539,6 +3539,7 @@ void fuse_init_file_inode(struct inode *inode, unsigned int flags)
 	INIT_LIST_HEAD(&fi->queued_writes);
 	fi->writectr = 0;
 	fi->iocachectr = 0;
+	fi->iopassctr = 0;
 	init_waitqueue_head(&fi->page_waitq);
 	init_waitqueue_head(&fi->direct_io_waitq);
 	fi->writepages = RB_ROOT;

fs/fuse/fuse_i.h

@@ -195,6 +195,9 @@ struct fuse_inode {
 			/** Number of files/maps using page cache */
 			int iocachectr;
 
+			/* Number of files using passthrough */
+			int iopassctr;
+
 			/* Waitq for writepage completion */
 			wait_queue_head_t page_waitq;
 
@@ -328,7 +331,7 @@ struct fuse_file {
 	wait_queue_head_t poll_wait;
 
 	/** Does file hold a fi->iocachectr refcount? */
-	enum { IOM_NONE, IOM_CACHED, IOM_UNCACHED } iomode;
+	enum { IOM_NONE, IOM_CACHED, IOM_UNCACHED, IOM_PASSTHROUGH } iomode;
 
 #ifdef CONFIG_FUSE_PASSTHROUGH
 	/** Reference to backing file in passthrough mode */

fs/fuse/inode.c

@@ -184,6 +184,7 @@ static void fuse_evict_inode(struct inode *inode)
 	}
 	if (S_ISREG(inode->i_mode) && !fuse_is_bad(inode)) {
 		WARN_ON(fi->iocachectr != 0);
+		WARN_ON(fi->iopassctr != 0);
 		WARN_ON(!list_empty(&fi->write_files));
 		WARN_ON(!list_empty(&fi->queued_writes));
 	}

fs/fuse/iomode.c

@@ -62,6 +62,7 @@ int fuse_file_cached_io_open(struct inode *inode, struct fuse_file *ff)
 #endif
 
 	WARN_ON(ff->iomode == IOM_UNCACHED);
+	WARN_ON(ff->iomode == IOM_PASSTHROUGH);
 	if (ff->iomode == IOM_NONE) {
 		ff->iomode = IOM_CACHED;
 		if (fi->iocachectr == 0)
@@ -85,7 +86,7 @@ static void fuse_file_cached_io_release(struct fuse_file *ff,
 	spin_unlock(&fi->lock);
 }
 
-/* Start strictly uncached io mode where cache access is not allowed */
+/* Start strictly uncached io mode where cache access is not allowed if not in passthrough mode */
 int fuse_inode_uncached_io_start(struct fuse_inode *fi, struct fuse_backing *fb)
 {
 	struct fuse_backing *oldfb;
@@ -98,11 +99,14 @@ int fuse_inode_uncached_io_start(struct fuse_inode *fi, struct fuse_backing *fb)
 		err = -EBUSY;
 		goto unlock;
 	}
-	if (fi->iocachectr > 0) {
+	if (!fb && fi->iocachectr > 0) {
 		err = -ETXTBSY;
 		goto unlock;
 	}
-	fi->iocachectr--;
+	if (fb)
+		fi->iopassctr++;
+	else
+		fi->iocachectr--;
 
 	/* fuse inode holds a single refcount of backing file */
 	if (fb && !oldfb) {
@@ -129,7 +133,7 @@ static int fuse_file_uncached_io_open(struct inode *inode,
 		return err;
 
 	WARN_ON(ff->iomode != IOM_NONE);
-	ff->iomode = IOM_UNCACHED;
+	ff->iomode = IOM_PASSTHROUGH;
 	return 0;
 }
 
@@ -158,6 +162,30 @@ static void fuse_file_uncached_io_release(struct fuse_file *ff,
 	fuse_inode_uncached_io_end(fi);
 }
 
+static void fuse_inode_passthrough_io_end(struct fuse_inode *fi)
+{
+	struct fuse_backing *oldfb = NULL;
+
+	spin_lock(&fi->lock);
+	WARN_ON(fi->iopassctr == 0);
+	fi->iopassctr--;
+	if (!fi->iopassctr) {
+		oldfb = fuse_inode_backing_set(fi, NULL);
+	}
+	spin_unlock(&fi->lock);
+	if (oldfb)
+		fuse_backing_put(oldfb);
+}
+
+/* Drop uncached_io reference from passthrough open */
+static void fuse_file_passthrough_io_release(struct fuse_file *ff,
+					  struct fuse_inode *fi)
+{
+	WARN_ON(ff->iomode != IOM_PASSTHROUGH);
+	ff->iomode = IOM_NONE;
+	fuse_inode_passthrough_io_end(fi);
+}
+
 /*
  * Open flags that are allowed in combination with FOPEN_PASSTHROUGH.
  * A combination of FOPEN_PASSTHROUGH and FOPEN_DIRECT_IO means that read/write
@@ -167,7 +195,7 @@ static void fuse_file_uncached_io_release(struct fuse_file *ff,
  */
 #define FOPEN_PASSTHROUGH_MASK \
 	(FOPEN_PASSTHROUGH | FOPEN_DIRECT_IO | FOPEN_PARALLEL_DIRECT_WRITES | \
-	 FOPEN_NOFLUSH)
+	 FOPEN_NOFLUSH | FOPEN_KEEP_CACHE)
 
 static int fuse_file_passthrough_open(struct inode *inode, struct file *file)
 {
@@ -277,5 +305,8 @@ void fuse_file_io_release(struct fuse_file *ff, struct inode *inode)
 	case IOM_CACHED:
 		fuse_file_cached_io_release(ff, fi);
 		break;
+	case IOM_PASSTHROUGH:
+		fuse_file_passthrough_io_release(ff, fi);
+		break;
 	}
 }