If two files to be compared share the same inode, it should be reasonable to consider them identical.
This gives a substantial speedup when comparing directory structures with many hardlinked files, e.g. when using rsnapshot for incremental backup. Comments? OK? /Alexander Index: diffreg.c =================================================================== RCS file: /cvs/src/usr.bin/diff/diffreg.c,v retrieving revision 1.93 diff -u -p -r1.93 diffreg.c --- diffreg.c 28 Jun 2019 13:35:00 -0000 1.93 +++ diffreg.c 31 Aug 2021 23:07:51 -0000 @@ -429,6 +429,10 @@ files_differ(FILE *f1, FILE *f2, int fla if ((flags & (D_EMPTY1|D_EMPTY2)) || stb1.st_size != stb2.st_size || (stb1.st_mode & S_IFMT) != (stb2.st_mode & S_IFMT)) return (1); + + if (stb1.st_dev == stb2.st_dev && stb1.st_ino == stb2.st_ino) + return (0); + for (;;) { i = fread(buf1, 1, sizeof(buf1), f1); j = fread(buf2, 1, sizeof(buf2), f2);