On Mon, Jan 25, 2021 at 4:31 PM Alessio Balsini <balsini@xxxxxxxxxxx> wrote: > > 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@xxxxxxx/ > > Signed-off-by: Alessio Balsini <balsini@xxxxxxxxxxx> > --- > fs/fuse/file.c | 3 +++ > fs/fuse/fuse_i.h | 1 + > fs/fuse/passthrough.c | 41 +++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 45 insertions(+) > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > index cddada1e8bd9..e3741a94c1f9 100644 > --- a/fs/fuse/file.c > +++ b/fs/fuse/file.c > @@ -2370,6 +2370,9 @@ static int fuse_file_mmap(struct file *file, struct vm_area_struct *vma) > if (FUSE_IS_DAX(file_inode(file))) > return fuse_dax_mmap(file, vma); > > + 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) > diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h > index 815af1845b16..7b0d65984608 100644 > --- a/fs/fuse/fuse_i.h > +++ b/fs/fuse/fuse_i.h > @@ -1244,5 +1244,6 @@ 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 */ > diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c > index 24866c5fe7e2..284979f87747 100644 > --- a/fs/fuse/passthrough.c > +++ b/fs/fuse/passthrough.c > @@ -135,6 +135,47 @@ 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; Again, violation of rules. Not sure why this is needed, mmap(2) isn't supposed to change mtime or ctime, AFAIK. Thanks, Miklos
