linux-kernel - Re: [PATCH v2] erofs: update ctx->pos for every emitted dirent

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Message-ID: <YrBl4CMZUiO6YqNM@B-P7TQMD6M-0146.local>
Date:   Mon, 20 Jun 2022 20:19:44 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     hongnanLi <hongnan.li@...ux.alibaba.com>
Cc:     Chao Yu <chao@...nel.org>, linux-erofs@...ts.ozlabs.org,
        xiang@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] erofs: update ctx->pos for every emitted dirent

Hi Hongnan,

On Mon, Jun 20, 2022 at 05:37:07PM +0800, hongnanLi wrote:
> on 2022/6/19 8:19, Chao Yu wrote:
> > On 2022/6/9 11:40, Hongnan Li wrote:
> > > erofs_readdir update ctx->pos after filling a batch of dentries
> > > and it may cause dir/files duplication for NFS readdirplus which
> > > depends on ctx->pos to fill dir correctly. So update ctx->pos for
> > > every emitted dirent in erofs_fill_dentries to fix it.
> > > 
> > > Fixes: 3e917cc305c6 ("erofs: make filesystem exportable")
> > > Signed-off-by: Hongnan Li <hongnan.li@...ux.alibaba.com>
> > > ---
> > >   fs/erofs/dir.c | 20 ++++++++++----------
> > >   1 file changed, 10 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/fs/erofs/dir.c b/fs/erofs/dir.c
> > > index 18e59821c597..94ef5287237a 100644
> > > --- a/fs/erofs/dir.c
> > > +++ b/fs/erofs/dir.c
> > > @@ -22,10 +22,9 @@ static void debug_one_dentry(unsigned char
> > > d_type, const char *de_name,
> > >   }
> > >   static int erofs_fill_dentries(struct inode *dir, struct
> > > dir_context *ctx,
> > > -                   void *dentry_blk, unsigned int *ofs,
> > > +                   void *dentry_blk, struct erofs_dirent *de,
> > >                      unsigned int nameoff, unsigned int maxsize)
> > >   {
> > > -    struct erofs_dirent *de = dentry_blk + *ofs;
> > >       const struct erofs_dirent *end = dentry_blk + nameoff;
> > >       while (de < end) {
> > > @@ -59,9 +58,8 @@ static int erofs_fill_dentries(struct inode *dir,
> > > struct dir_context *ctx,
> > >               /* stopped by some reason */
> > >               return 1;
> > >           ++de;
> > > -        *ofs += sizeof(struct erofs_dirent);
> > > +        ctx->pos += sizeof(struct erofs_dirent);
> > >       }
> > > -    *ofs = maxsize;
> > >       return 0;
> > >   }
> > > @@ -95,7 +93,7 @@ static int erofs_readdir(struct file *f, struct
> > > dir_context *ctx)
> > >                     "invalid de[0].nameoff %u @ nid %llu",
> > >                     nameoff, EROFS_I(dir)->nid);
> > >               err = -EFSCORRUPTED;
> > > -            goto skip_this;
> > > +            break;
> > >           }
> > >           maxsize = min_t(unsigned int,
> > > @@ -106,17 +104,19 @@ static int erofs_readdir(struct file *f,
> > > struct dir_context *ctx)
> > >               initial = false;
> > >               ofs = roundup(ofs, sizeof(struct erofs_dirent));
> > > -            if (ofs >= nameoff)
> > > +            if (ofs >= nameoff) {
> > > +                ctx->pos = blknr_to_addr(i) + ofs;
> > >                   goto skip_this;
> > > +            }
> > >           }
> > > -        err = erofs_fill_dentries(dir, ctx, de, &ofs,
> > > -                      nameoff, maxsize);
> > > -skip_this:
> > >           ctx->pos = blknr_to_addr(i) + ofs;
> > 
> > Why updating ctx->pos before erofs_fill_dentries()?
> > 
> > Thanks,
> 
> It’s to ensure the ctx->pos is correct and up to date in
> erofs_fill_dentries() so that we can update ctx->pos instead of ofs for
> every emitted dirent.
> 

How about this, since blknr_to_addr(i) + maxsize should be the start of
the next dir block.

	if (initial) {
		ofs = roundup(ofs, sizeof(struct erofs_dirent));
		ctx->pos = blknr_to_addr(i) + ofs;
		if (ofs >= nameoff)
			goto skip_this;
	}
	err = erofs_fill_dentries(dir, ctx, de, (void *)de + ofs,
				  nameoff, maxsize);
	if (err)
		break;
	ctx->pos = blknr_to_addr(i) + maxsize;

Thanks,
Gao Xiang