Re: [PATCH v5 14/23] fanotify: Encode invalid file handler when no inode is provided

On Wed 11-08-21 17:12:05, Gabriel Krisman Bertazi wrote:

Jan Kara [off-list ref] writes:

quoted

quoted

@@ -376,14 +371,24 @@ static int fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode,
 		fh->flags |= FANOTIFY_FH_FLAG_EXT_BUF;
 	}
 
-	dwords = fh_len >> 2;
-	type = exportfs_encode_inode_fh(inode, buf, &dwords, NULL);
-	err = -EINVAL;
-	if (!type || type == FILEID_INVALID || fh_len != dwords << 2)
-		goto out_err;
-
-	fh->type = type;
-	fh->len = fh_len;
+	if (inode) {
+		dwords = fh_len >> 2;
+		type = exportfs_encode_inode_fh(inode, buf, &dwords, NULL);
+		err = -EINVAL;
+		if (!type || type == FILEID_INVALID || fh_len != dwords << 2)
+			goto out_err;
+		fh->type = type;
+		fh->len = fh_len;
+	} else {
+		/*
+		 * Invalid FHs are used on FAN_FS_ERROR for errors not
+		 * linked to any inode. Caller needs to guarantee the fh
+		 * has at least FANOTIFY_NULL_FH_LEN bytes of space.
+		 */
+		fh->type = FILEID_INVALID;
+		fh->len = FANOTIFY_NULL_FH_LEN;
+		memset(buf, 0, FANOTIFY_NULL_FH_LEN);
+	}

Maybe it will become clearer later during the series but why do you set
fh->len to FANOTIFY_NULL_FH_LEN and not 0?

Jan,

That is how we encode a NULL file handle (i.e. superblock error).  Amir
suggested it would be an invalid FILEID_INVALID, with a zeroed handle of
size 8.  I will improve the comment on the next iteration.

Thanks for info. Then I have a question for Amir I guess :) Amir, what's
the advantage of zeroed handle of size 8 instead of just 0 length file
handle?

								Honza

-- 
Jan Kara [off-list ref]
SUSE Labs, CR