[PATCH 3/3] fuse: prepare for long lived reference on backing file

[Amir Goldstein <amir73il@gmail.com>]

Currently backing file is associated to fuse inode on the first
passthrough open of the inode and detached on last passthourgh close.

In preparation for attaching a backing file on lookup, allow attaching
a long lived (single) reference on fuse inode backing file that will be
dropped on fuse inode evict.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/fuse/file.c   |  2 +-
 fs/fuse/fuse_i.h |  5 ++++-
 fs/fuse/inode.c  |  6 ++++++
 fs/fuse/iomode.c | 14 +++++++++++---
 4 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index fcf20b304093..347bae2b287f 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1377,7 +1377,7 @@ static void fuse_dio_lock(struct kiocb *iocb, struct iov_iter *from,
 		 * have raced, so check it again.
 		 */
 		if (fuse_io_past_eof(iocb, from) ||
-		    fuse_inode_uncached_io_start(fi, NULL) != 0) {
+		    fuse_inode_uncached_io_start(fi, NULL, false) != 0) {
 			inode_unlock_shared(inode);
 			inode_lock(inode);
 			*exclusive = true;
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index f23919610313..2f340fd05e8a 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -209,6 +209,8 @@ enum {
 	FUSE_I_BTIME,
 	/* Wants or already has page cache IO */
 	FUSE_I_CACHE_IO_MODE,
+	/* Long lived backing file */
+	FUSE_I_BACKING,
 };
 
 struct fuse_conn;
@@ -1396,7 +1398,8 @@ int fuse_fileattr_set(struct mnt_idmap *idmap,
 /* iomode.c */
 int fuse_file_cached_io_open(struct inode *inode, struct fuse_file *ff);
 int fuse_inode_uncached_io_start(struct fuse_inode *fi,
-				 struct fuse_backing *fb);
+				 struct fuse_backing *fb,
+				 bool keep_fb);
 void fuse_inode_uncached_io_end(struct fuse_inode *fi);
 
 int fuse_file_io_open(struct file *file, struct inode *inode);
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 99e44ea7d875..989a84f6a825 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -175,6 +175,12 @@ static void fuse_evict_inode(struct inode *inode)
 		}
 	}
 	if (S_ISREG(inode->i_mode) && !fuse_is_bad(inode)) {
+		/* fuse inode may have a long lived reference to backing file */
+		if (fuse_inode_backing(fi)) {
+			WARN_ON(!test_bit(FUSE_I_BACKING, &fi->state));
+			fuse_inode_uncached_io_end(fi);
+		}
+
 		WARN_ON(fi->iocachectr != 0);
 		WARN_ON(!list_empty(&fi->write_files));
 		WARN_ON(!list_empty(&fi->queued_writes));
diff --git a/fs/fuse/iomode.c b/fs/fuse/iomode.c
index f9e30c4540af..b1ff43668800 100644
--- a/fs/fuse/iomode.c
+++ b/fs/fuse/iomode.c
@@ -80,8 +80,14 @@ 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 */
-int fuse_inode_uncached_io_start(struct fuse_inode *fi, struct fuse_backing *fb)
+/*
+ * Start strictly uncached io mode where cache access is not allowed.
+ *
+ * With @keep_fb true, the backing file reference is expected to be dropped
+ * on inode evict.
+ */
+int fuse_inode_uncached_io_start(struct fuse_inode *fi, struct fuse_backing *fb,
+				 bool keep_fb)
 {
 	struct fuse_backing *oldfb;
 	int err = 0;
@@ -103,6 +109,8 @@ int fuse_inode_uncached_io_start(struct fuse_inode *fi, struct fuse_backing *fb)
 	if (fb && !oldfb) {
 		oldfb = fuse_inode_backing_set(fi, fb);
 		WARN_ON_ONCE(oldfb != NULL);
+		if (keep_fb)
+			set_bit(FUSE_I_BACKING, &fi->state);
 	} else {
 		fuse_backing_put(fb);
 	}
@@ -119,7 +127,7 @@ static int fuse_file_uncached_io_open(struct inode *inode,
 	struct fuse_inode *fi = get_fuse_inode(inode);
 	int err;
 
-	err = fuse_inode_uncached_io_start(fi, fb);
+	err = fuse_inode_uncached_io_start(fi, fb, false);
 	if (err)
 		return err;
 
-- 
2.34.1