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Unverified Commit 5d232ddb authored by Alessio Balsini's avatar Alessio Balsini Committed by Michael Bestas
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FROMLIST: fuse: Introduce passthrough for mmap 

Enabling FUSE passthrough for mmap-ed operations not only affects
performance, but has also been shown as mandatory for the correct
functioning of FUSE passthrough.
yanwu noticed [1] that a FUSE file with passthrough enabled may suffer
data inconsistencies if the same file is also accessed with mmap. What
happens is that read/write operations are directly applied to the lower
file system (and its cache), while mmap-ed operations are affecting the
FUSE cache.

Extend the FUSE passthrough implementation to also handle memory-mapped
FUSE file, to both fix the cache inconsistencies and extend the
passthrough performance benefits to mmap-ed operations.

[1] https://lore.kernel.org/lkml/20210119110654.11817-1-wu-yan@tcl.com/

Bug: 168023149
Link: https://lore.kernel.org/lkml/20210125153057.3623715-9-balsini@android.com/


Signed-off-by: default avatarAlessio Balsini <balsini@android.com>
Change-Id: Ifad4698b0380f6e004c487940ac6907b9a9f2964
Signed-off-by: default avatarAlessio Balsini <balsini@google.com>
parent 2d336e55

fs/fuse/file.c

+3 −0
Original line number Diff line number Diff line
@@ -2330,6 +2330,9 @@ static int fuse_file_mmap(struct file *file, struct vm_area_struct *vma) 
{

	struct fuse_file *ff = file->private_data;



	if (ff->passthrough.filp)

		return fuse_passthrough_mmap(file, vma);



	if (ff->open_flags & FOPEN_DIRECT_IO) {

		/* Can't provide the coherency needed for MAP_SHARED */

		if (vma->vm_flags & VM_MAYSHARE)

fs/fuse/fuse_i.h

+1 −0
Original line number Diff line number Diff line
@@ -1142,5 +1142,6 @@ int fuse_passthrough_setup(struct fuse_conn *fc, struct fuse_file *ff, 
void fuse_passthrough_release(struct fuse_passthrough *passthrough);

ssize_t fuse_passthrough_read_iter(struct kiocb *iocb, struct iov_iter *to);

ssize_t fuse_passthrough_write_iter(struct kiocb *iocb, struct iov_iter *from);

ssize_t fuse_passthrough_mmap(struct file *file, struct vm_area_struct *vma);



#endif /* _FS_FUSE_I_H */

fs/fuse/passthrough.c

+41 −0
Original line number Diff line number Diff line
@@ -147,6 +147,47 @@ ssize_t fuse_passthrough_write_iter(struct kiocb *iocb_fuse, 
	return ret;

}



ssize_t fuse_passthrough_mmap(struct file *file, struct vm_area_struct *vma)

{

	int ret;

	const struct cred *old_cred;

	struct fuse_file *ff = file->private_data;

	struct inode *fuse_inode = file_inode(file);

	struct file *passthrough_filp = ff->passthrough.filp;

	struct inode *passthrough_inode = file_inode(passthrough_filp);



	if (!passthrough_filp->f_op->mmap)

		return -ENODEV;



	if (WARN_ON(file != vma->vm_file))

		return -EIO;



	vma->vm_file = get_file(passthrough_filp);



	old_cred = override_creds(ff->passthrough.cred);

	ret = call_mmap(vma->vm_file, vma);

	revert_creds(old_cred);



	if (ret)

		fput(passthrough_filp);

	else

		fput(file);



	if (file->f_flags & O_NOATIME)

		return ret;



	if ((!timespec64_equal(&fuse_inode->i_mtime,

			       &passthrough_inode->i_mtime) ||

	     !timespec64_equal(&fuse_inode->i_ctime,

			       &passthrough_inode->i_ctime))) {

		fuse_inode->i_mtime = passthrough_inode->i_mtime;

		fuse_inode->i_ctime = passthrough_inode->i_ctime;

	}

	touch_atime(&file->f_path);



	return ret;

}



int fuse_passthrough_open(struct fuse_dev *fud,

			  struct fuse_passthrough_out *pto)

{