erofs: update ctx->pos for every emitted dirent

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.

Also fix the update of ctx->pos when the initial file position has
exceeded nameoff.

Fixes: 3e917cc3 ("erofs: make filesystem exportable")
Signed-off-by: Hongnan Li <hongnan.li@linux.alibaba.com>
Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20220722082732.30935-1-jefflexu@linux.alibaba.comSigned-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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 +104,17 @@ static int erofs_readdir(struct file *f, struct dir_context *ctx)
 			initial = false;
 
 			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, &ofs,
+		err = erofs_fill_dentries(dir, ctx, de, (void *)de + ofs,
 					  nameoff, maxsize);
-skip_this:
-		ctx->pos = blknr_to_addr(i) + ofs;
-
 		if (err)
 			break;
+skip_this:
+		ctx->pos = blknr_to_addr(i) + maxsize;
 		++i;
 		ofs = 0;
 	}