linux-kernel - Re: [PATCH] exfat: fdatasync flag should be same like generic_write

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Message-ID:
 <PUZPR04MB6316B9353121616B7C0928D98172A@PUZPR04MB6316.apcprd04.prod.outlook.com>
Date: Wed, 18 Jun 2025 11:11:04 +0000
From: "Yuezhang.Mo@...y.com" <Yuezhang.Mo@...y.com>
To: 张政旭 (Zhengxu Zhang)
	<Zhengxu.Zhang@...soc.com>,
        Cixi Geng <cixi.geng@...ux.dev>,
        "linkinjeon@...nel.org" <linkinjeon@...nel.org>,
        "sj1557.seo@...sung.com"
	<sj1557.seo@...sung.com>
CC: "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        王皓 (Hao_hao Wang) <Hao_hao.Wang@...soc.com>,
        牛志国 (Zhiguo Niu) <Zhiguo.Niu@...soc.com>
Subject: Re: [PATCH] exfat: fdatasync flag should be same like
 generic_write_sync()

> > > > > --- a/fs/exfat/file.c
> > > > > +++ b/fs/exfat/file.c
> > > > > @@ -625,7 +625,7 @@ static ssize_t exfat_file_write_iter(struct kiocb *iocb,
> > > > > struct iov_iter *iter)
> > > > >
> > > > >        if (iocb_is_dsync(iocb) && iocb->ki_pos > pos) {
> > > > >                 ssize_t err = vfs_fsync_range(file, pos, iocb->ki_pos - 1,
> > > > > -                               iocb->ki_flags & IOCB_SYNC);
> > > > > +                               (iocb->ki_flags & IOCB_SYNC) ? 0 : 1);
> > > >
> > > > How about calling generic_write_sync() instead of vfs_fsync_range(), like in
> > > > generic_file_write_iter()?
> > > The second arg of vfs_fsync_range "pos" maybe changed by valid_size (if pos >
> > valid_size).
> > > It can not replace by iocb->ki_pos - ret (ret by __generic_file_write_iter).
> > > So current way maybe better.
> >
> > Here we synchronize the areas written by exfat_extend_valid_size() and
> > __generic_file_write_iter() if valid_size < pos.
> >
> > The lengths of these two write areas are 'pos-valid_size' and 'ret'.
> > We can use generic_write_sync() and pass it the sum of these two lengths.
> > 
> > Of course, regardless of whether valid_size < pos, exfat_file_write_iter() only
> > needs to return the length written by __generic_file_write_iter().
> 
> I try the sum of 'pos-valid_size' and 'ret',like this:
>         if (iocb->ki_pos > pos) {
>                 ssize_t err = generic_write_sync(iocb, pos + ret - valid_size);
>                 if (err < 0)
>                         return err;
>         }
> The test crashed, that maybe io error.

I think the crash happens when pos < valid_size, because exfat_extend_valid_size()
does not write data in this case.

> So I try a simple way that use iocb->ki_pos - pos. like this:
>         if (iocb->ki_pos > pos) {
>                 ssize_t err = generic_write_sync(iocb, iocb->ki_pos - pos);
>                 if (err < 0)
>                         return err;
>         }
> The test pass. pls check again.

'pos' is set to the write position of exfat_extend_valid_size() by:

if (pos > valid_size)
          pos = valid_size;

'iocb->ki_pos - pos' is the total write length, this way is fine.