Enhance file_id_t to have richer information, to guard against inode

recycling on Linux filesystems

1 files changed, 18 insertions, 2 deletions

diff --git a/wutil.h b/wutil.h
index 1b2f6f2b..3355ab14 100644
--- a/wutil.h
+++ b/wutil.h
@@ -158,8 +158,24 @@ int wrename(const wcstring &oldName, const wcstring &newName);
 /** Like wcstol(), but fails on a value outside the range of an int */
 int fish_wcstoi(const wchar_t *str, wchar_t ** endptr, int base);
 
-/** Class for representing a file's inode. We use this to detect and avoid symlink loops, among other things. */
-typedef std::pair<dev_t, ino_t> file_id_t;
+/** Class for representing a file's inode. We use this to detect and avoid symlink loops, among other things. While an inode / dev pair is sufficient to distinguish co-existing files, Linux seems to aggressively re-use inodes, so it cannot determine if a file has been deleted (ABA problem). Therefore we include richer information. */
+struct file_id_t
+{
+    dev_t device;
+    ino_t inode;
+    uint64_t size;
+    time_t change_seconds;
+    long change_nanoseconds;
+    uint32_t generation;
+    
+    bool operator==(const file_id_t &rhs) const;
+    bool operator!=(const file_id_t &rhs) const;
+    
+    // Used to permit these as keys in std::map
+    bool operator<(const file_id_t &rhs) const;
+    
+    static file_id_t file_id_from_stat(const struct stat *buf);
+};
 
 file_id_t file_id_for_fd(int fd);
 file_id_t file_id_for_path(const wcstring &path);