[PATCH v15 6/9] fuse: implement read/write passthrough

[Amir Goldstein <amir73il@gmail.com>]

Use the backing file read/write helpers to implement read/write
passthrough to a backing file.

After read/write, we invalidate a/c/mtime/size attributes if the
backing inode attributes differ from FUSE inode attributes.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/fuse/file.c        | 18 ++++++---
 fs/fuse/fuse_i.h      |  3 ++
 fs/fuse/passthrough.c | 86 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 101 insertions(+), 6 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index bdcee82fef9a..0f7c53ea2f13 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1688,10 +1688,13 @@ static ssize_t fuse_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	if (FUSE_IS_DAX(inode))
 		return fuse_dax_read_iter(iocb, to);
 
-	if (!(ff->open_flags & FOPEN_DIRECT_IO))
-		return fuse_cache_read_iter(iocb, to);
-	else
+	/* FOPEN_DIRECT_IO overrides FOPEN_PASSTHROUGH */
+	if (ff->open_flags & FOPEN_DIRECT_IO)
 		return fuse_direct_read_iter(iocb, to);
+	else if (fuse_file_passthrough(ff))
+		return fuse_passthrough_read_iter(iocb, to);
+	else
+		return fuse_cache_read_iter(iocb, to);
 }
 
 static ssize_t fuse_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
@@ -1706,10 +1709,13 @@ static ssize_t fuse_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	if (FUSE_IS_DAX(inode))
 		return fuse_dax_write_iter(iocb, from);
 
-	if (!(ff->open_flags & FOPEN_DIRECT_IO))
-		return fuse_cache_write_iter(iocb, from);
-	else
+	/* FOPEN_DIRECT_IO overrides FOPEN_PASSTHROUGH */
+	if (ff->open_flags & FOPEN_DIRECT_IO)
 		return fuse_direct_write_iter(iocb, from);
+	else if (fuse_file_passthrough(ff))
+		return fuse_passthrough_write_iter(iocb, from);
+	else
+		return fuse_cache_write_iter(iocb, from);
 }
 
 static void fuse_writepage_free(struct fuse_writepage_args *wpa)
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 407b24c79ebb..e47d7e8e4285 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1471,4 +1471,7 @@ static inline struct file *fuse_file_passthrough(struct fuse_file *ff)
 #endif
 }
 
+ssize_t fuse_passthrough_read_iter(struct kiocb *iocb, struct iov_iter *iter);
+ssize_t fuse_passthrough_write_iter(struct kiocb *iocb, struct iov_iter *iter);
+
 #endif /* _FS_FUSE_I_H */
diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
index 098a1f765e99..206eedbf6bf8 100644
--- a/fs/fuse/passthrough.c
+++ b/fs/fuse/passthrough.c
@@ -10,6 +10,92 @@
 #include <linux/file.h>
 #include <linux/backing-file.h>
 
+static void fuse_file_accessed(struct file *file)
+{
+	struct inode *inode = file_inode(file);
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	struct fuse_backing *fb = fuse_inode_backing(fi);
+	struct inode *backing_inode = file_inode(fb->file);
+	struct timespec64 atime = inode_get_atime(inode);
+	struct timespec64 batime = inode_get_atime(backing_inode);
+
+	/* Mimic atime update policy of backing inode, not the actual value */
+	if (!timespec64_equal(&batime, &atime))
+		fuse_invalidate_atime(inode);
+}
+
+static void fuse_file_modified(struct file *file)
+{
+	struct inode *inode = file_inode(file);
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	struct fuse_backing *fb = fuse_inode_backing(fi);
+	struct inode *backing_inode = file_inode(fb->file);
+	struct timespec64 ctime = inode_get_ctime(inode);
+	struct timespec64 mtime = inode_get_mtime(inode);
+	struct timespec64 bctime = inode_get_ctime(backing_inode);
+	struct timespec64 bmtime = inode_get_mtime(backing_inode);
+
+	if (!timespec64_equal(&bctime, &ctime) ||
+	    !timespec64_equal(&bmtime, &mtime) ||
+	    i_size_read(backing_inode) != i_size_read(inode))
+		fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE);
+}
+
+ssize_t fuse_passthrough_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	struct file *file = iocb->ki_filp;
+	struct fuse_file *ff = file->private_data;
+	struct file *backing_file = fuse_file_passthrough(ff);
+	size_t count = iov_iter_count(iter);
+	ssize_t ret;
+	struct backing_file_ctx ctx = {
+		.cred = ff->cred,
+		.user_file = file,
+		.accessed = fuse_file_accessed,
+	};
+
+
+	pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu\n", __func__,
+		 backing_file, iocb->ki_pos, count);
+
+	if (!count)
+		return 0;
+
+	ret = backing_file_read_iter(backing_file, iter, iocb, iocb->ki_flags,
+				     &ctx);
+
+	return ret;
+}
+
+ssize_t fuse_passthrough_write_iter(struct kiocb *iocb,
+				    struct iov_iter *iter)
+{
+	struct file *file = iocb->ki_filp;
+	struct inode *inode = file_inode(file);
+	struct fuse_file *ff = file->private_data;
+	struct file *backing_file = fuse_file_passthrough(ff);
+	size_t count = iov_iter_count(iter);
+	ssize_t ret;
+	struct backing_file_ctx ctx = {
+		.cred = ff->cred,
+		.user_file = file,
+		.end_write = fuse_file_modified,
+	};
+
+	pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu\n", __func__,
+		 backing_file, iocb->ki_pos, count);
+
+	if (!count)
+		return 0;
+
+	inode_lock(inode);
+	ret = backing_file_write_iter(backing_file, iter, iocb, iocb->ki_flags,
+				      &ctx);
+	inode_unlock(inode);
+
+	return ret;
+}
+
 struct fuse_backing *fuse_backing_get(struct fuse_backing *fb)
 {
 	if (fb && refcount_inc_not_zero(&fb->count))
-- 
2.34.1