fanotify: copy event fid info to user

If group requested FAN_REPORT_FID and event has file identifier,
copy that information to user reading the event after event metadata.

fid information is formatted as struct fanotify_event_info_fid
that includes a generic header struct fanotify_event_info_header,
so that other info types could be defined in the future using the
same header.

metadata->event_len includes the length of the fid information.

The fid information includes the filesystem's fsid (see statfs(2))
followed by an NFS file handle of the file that could be passed as
an argument to open_by_handle_at(2).

Cc: <linux-api@vger.kernel.org>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 20 insertions, 0 deletions

diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
index d07f3cbc2786..959ae2bdc7ca 100644
--- a/include/uapi/linux/fanotify.h
+++ b/include/uapi/linux/fanotify.h
@@ -107,6 +107,26 @@ struct fanotify_event_metadata {
 	__s32 pid;
 };
 
+#define FAN_EVENT_INFO_TYPE_FID		1
+
+/* Variable length info record following event metadata */
+struct fanotify_event_info_header {
+	__u8 info_type;
+	__u8 pad;
+	__u16 len;
+};
+
+/* Unique file identifier info record */
+struct fanotify_event_info_fid {
+	struct fanotify_event_info_header hdr;
+	__kernel_fsid_t fsid;
+	/*
+	 * Following is an opaque struct file_handle that can be passed as
+	 * an argument to open_by_handle_at(2).
+	 */
+	unsigned char handle[0];
+};
+
 struct fanotify_response {
 	__s32 fd;
 	__u32 response;