linux-kernel - Re: [PATCH -next,v2] fuse: return the more nuanced writeback error on close()

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Date:   Mon, 30 May 2022 16:38:24 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        ChenXiaoSong <chenxiaosong2@...wei.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        liuyongqiang13@...wei.com, "zhangyi (F)" <yi.zhang@...wei.com>,
        zhangxiaoxu5@...wei.com, Steve French <smfrench@...il.com>,
        NeilBrown <neilb@...e.de>
Subject: Re: [PATCH -next,v2] fuse: return the more nuanced writeback error
 on close()

On Mon, May 30, 2022 at 10:02:06AM -0400, Jeff Layton wrote:

> 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.
> 
> 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
> 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.

Thanks for clarifying.

Chen, would the following patch make sense for your case?

Thanks,
Miklos

---
 fs/fuse/file.c |    5 -----
 1 file changed, 5 deletions(-)

--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -487,11 +487,6 @@ static int fuse_flush(struct file *file,
 	fuse_sync_writes(inode);
 	inode_unlock(inode);
 
-	err = filemap_check_errors(file->f_mapping);
-	if (err)
-		return err;
-
-	err = 0;
 	if (fm->fc->no_flush)
 		goto inval_attr_out;