linux-kernel - Re: [PATCH V9 3/4] fuse: Introduce synchronous read and write for passthrough

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Date:   Thu, 22 Oct 2020 17:17:45 +0100
From:   Alessio Balsini <balsini@...roid.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     Alessio Balsini <balsini@...roid.com>,
        Akilesh Kailash <akailash@...gle.com>,
        Amir Goldstein <amir73il@...il.com>,
        Antonio SJ Musumeci <trapexit@...wn.link>,
        David Anderson <dvander@...gle.com>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Jann Horn <jannh@...gle.com>, Jens Axboe <axboe@...nel.dk>,
        Martijn Coenen <maco@...roid.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Lawrence <paullawrence@...gle.com>,
        Stefano Duo <stefanoduo@...gle.com>,
        Zimuzo Ezeozue <zezeozue@...gle.com>,
        fuse-devel <fuse-devel@...ts.sourceforge.net>,
        kernel-team <kernel-team@...roid.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V9 3/4] fuse: Introduce synchronous read and write for
 passthrough

On Wed, Sep 30, 2020 at 08:50:46PM +0200, Miklos Szeredi wrote:
> > [...]
> > +ssize_t fuse_passthrough_read_iter(struct kiocb *iocb_fuse,
> > +                                  struct iov_iter *iter)
> > +{
> > +       ssize_t ret;
> > +       const struct cred *old_cred;
> > +       struct file *fuse_filp = iocb_fuse->ki_filp;
> > +       struct fuse_file *ff = fuse_filp->private_data;
> > +       struct file *passthrough_filp = ff->passthrough_filp;
> > +
> > +       if (!iov_iter_count(iter))
> > +               return 0;
> > +
> > +       old_cred = fuse_passthrough_override_creds(fuse_filp);
> > +       if (is_sync_kiocb(iocb_fuse)) {
> > +               ret = vfs_iter_read(passthrough_filp, iter, &iocb_fuse->ki_pos,
> > +                                   iocbflags_to_rwf(iocb_fuse->ki_flags));
> > +       } else {
> > +               ret = -EIO;
> > +       }
> 
> Just do vfs_iter_read() unconditionally, instead of returning EIO.
> It will work fine, except it won't be async.
> 
> Yeah, I know next patch is going to fix this, but still, lets not make
> this patch return silly errors.
> 
> > [...]
> > +ssize_t fuse_passthrough_write_iter(struct kiocb *iocb_fuse,
> > +                                   struct iov_iter *iter)
> > +{
> > +       ssize_t ret;
> > +       const struct cred *old_cred;
> > +       struct file *fuse_filp = iocb_fuse->ki_filp;
> > +       struct fuse_file *ff = fuse_filp->private_data;
> > +       struct inode *fuse_inode = file_inode(fuse_filp);
> > +       struct file *passthrough_filp = ff->passthrough_filp;
> > +
> > +       if (!iov_iter_count(iter))
> > +               return 0;
> > +
> > +       inode_lock(fuse_inode);
> > +
> > +       old_cred = fuse_passthrough_override_creds(fuse_filp);
> > +       if (is_sync_kiocb(iocb_fuse)) {
> > +               file_start_write(passthrough_filp);
> > +               ret = vfs_iter_write(passthrough_filp, iter, &iocb_fuse->ki_pos,
> > +                                   iocbflags_to_rwf(iocb_fuse->ki_flags));
> > +               file_end_write(passthrough_filp);
> > +               if (ret > 0)
> > +                       fuse_copyattr(fuse_filp, passthrough_filp);
> > +       } else {
> > +               ret = -EIO;
> > +       }
> 
> And the same here.
> 

Ack, adding both to the upcoming patch set.

Thanks,
Alessio