On Tue, 31 May 2022, Jeff Layton wrote:
> On Mon, 2022-05-30 at 14:13 +0200, Miklos Szeredi wrote:
> > On Mon, 23 May 2022 at 03:35, ChenXiaoSong <chenxiaosong2@xxxxxxxxxx> wrote:
> > >
> > > As filemap_check_errors() only report -EIO or -ENOSPC, we return more nuanced
> > > writeback error -(file->f_mapping->wb_err & MAX_ERRNO).
> > >
> > > filemap_write_and_wait
> > > filemap_write_and_wait_range
> > > filemap_check_errors
> > > -ENOSPC or -EIO
> > > filemap_check_wb_err
> > > errseq_check
> > > return -(file->f_mapping->wb_err & MAX_ERRNO)
> > >
> > > Signed-off-by: ChenXiaoSong <chenxiaosong2@xxxxxxxxxx>
> > > ---
> > > fs/fuse/file.c | 4 ++--
> > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> > > index f18d14d5fea1..9917bc2795e6 100644
> > > --- a/fs/fuse/file.c
> > > +++ b/fs/fuse/file.c
> > > @@ -488,10 +488,10 @@ static int fuse_flush(struct file *file, fl_owner_t id)
> > > inode_unlock(inode);
> > >
> > > err = filemap_check_errors(file->f_mapping);
> > > + /* return more nuanced writeback errors */
> > > if (err)
> > > - return err;
> > > + return filemap_check_wb_err(file->f_mapping, 0);
> >
> > I'm wondering if this should be file_check_and_advance_wb_err() instead.
> >
>
> I think that it probably shouldn't be, actually. Reason below...
>
> > Is there a difference between ->flush() and ->fsync()?
> >
> > Jeff, can you please help?
> >
> >
>
> The main difference is that ->flush is called from filp_close, so it's
> called when a file descriptor (or equivalent) is being torn down out,
> whereas ->fsync is (obviously) called from the fsync codepath.
->flush is for cache coherence. It is best-effort
->fsync is for data safety. Obviously errors are important.
>
> We _must_ report writeback errors on fsync, but reporting them on the
> close() syscall is less clear. The thing about close() is that it's
> going be successful no matter what is returned. The file descriptor will
> no longer work afterward regardless.
>
> fsync also must also initiate writeback of all the buffered data, but
> it's not required for filesystems to do that on close() (and in fact,
> there are good reasons not to if you can). A successful close() tells
> you nothing about whether your data made it to the backing store. It
> might just not have been synced out yet.
>
> Personally, I think it's probably best to _not_ return writeback errors
> on close at all. The only "legitimate" error on close is -EBADF.
> Arguably, we should make ->flush be void return. Note that most
^^^^^^^^^^^^^^^^^^^^^^^^^^^
Excellent idea!
NeilBrown
> filp_close callers ignore the error anyway, so it's not much of a
> stretch.
>
> In any case, if you do decide to return errors in fuse_flush, then
> advancing the cursor would also have the effect of masking writeback
> errors on dup()'ed file descriptors, and I don't think you want to do
> that.
> --
> Jeff Layton <jlayton@xxxxxxxxxx>
>
