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

[hongnanLi]

Hi Gao Xiang,

on 2022/6/20 下午8:19, Gao Xiang wrote:
> 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@xxxxxxxxxxxxxxxxx>
> > > > ---
> > > >    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 for your suggestion. It looks good and works well in my test. I 
will send PATCH v3 later if everything else is okay.

Thanks,
Hongnan Li