Some userspace programs use st_ino as a unique object identifier, even though inode numbers may be recycable. This issue has been addressed for NFS export long ago using the exportfs file handle API and the unique file handle identifiers are also exported to userspace via name_to_handle_at(2). fanotify also uses file handles to identify objects in events, but only for filesystems that support NFS export. Relax the requirement for NFS export support and allow more filesystems to export a unique object identifier via name_to_handle_at(2) with the flag AT_HANDLE_FID. A file handle requested with the AT_HANDLE_FID flag, may or may not be usable as an argument to open_by_handle_at(2). To allow filesystems to opt-in to supporting AT_HANDLE_FID, a struct export_operations is required, but even an empty struct is sufficient for encoding FIDs.
Showing the changes to include/uapi (1 of 2 files). Show all
Unified · Split
| @@ -112,4 +112,9 @@ · 111 unmodified lines | |||
| 112 | 112 | ||
| 113 | #define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */ | 113 | #define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */ |
| 114 | 114 | ||
| 115 | /* Flags for name_to_handle_at(2). We reuse AT_ flag space to save bits... */ | ||
| 116 | #define AT_HANDLE_FID AT_REMOVEDIR /* file handle is needed to | ||
| 117 | compare object identity and may not | ||
| 118 | be usable to open_by_handle_at(2) */ | ||
| 119 | |||
| 115 | #endif /* _UAPI_LINUX_FCNTL_H */ | 120 | #endif /* _UAPI_LINUX_FCNTL_H */ |