1 files changed, 47 insertions, 0 deletions

diff --git a/editors/diff.c b/editors/diff.c
index ca4a4eae7..daa58af9b 100644
--- a/editors/diff.c
+++ b/editors/diff.c
@@ -76,6 +76,28 @@
  * 6n words for files of length n.
  */
 
+//usage:#define diff_trivial_usage
+//usage:       "[-abBdiNqrTstw] [-L LABEL] [-S FILE] [-U LINES] FILE1 FILE2"
+//usage:#define diff_full_usage "\n\n"
+//usage:       "Compare files line by line and output the differences between them.\n"
+//usage:       "This implementation supports unified diffs only.\n"
+//usage:     "\nOptions:"
+//usage:     "\n        -a      Treat all files as text"
+//usage:     "\n        -b      Ignore changes in the amount of whitespace"
+//usage:     "\n        -B      Ignore changes whose lines are all blank"
+//usage:     "\n        -d      Try hard to find a smaller set of changes"
+//usage:     "\n        -i      Ignore case differences"
+//usage:     "\n        -L      Use LABEL instead of the filename in the unified header"
+//usage:     "\n        -N      Treat absent files as empty"
+//usage:     "\n        -q      Output only whether files differ"
+//usage:     "\n        -r      Recurse"
+//usage:     "\n        -S      Start with FILE when comparing directories"
+//usage:     "\n        -T      Make tabs line up by prefixing a tab when necessary"
+//usage:     "\n        -s      Report when two files are the same"
+//usage:     "\n        -t      Expand tabs to spaces in output"
+//usage:     "\n        -U      Output LINES lines of context"
+//usage:     "\n        -w      Ignore all whitespace"
+
 #include "libbb.h"
 
 #if 0
@@ -952,6 +974,31 @@ int diff_main(int argc UNUSED_PARAM, char **argv)
         if (gotstdin && (S_ISDIR(stb[0].st_mode) || S_ISDIR(stb[1].st_mode)))
                 bb_error_msg_and_die("can't compare stdin to a directory");
 
+        /* Compare metadata to check if the files are the same physical file.
+         *
+         * Comment from diffutils source says:
+         * POSIX says that two files are identical if st_ino and st_dev are
+         * the same, but many file systems incorrectly assign the same (device,
+         * inode) pair to two distinct files, including:
+         * GNU/Linux NFS servers that export all local file systems as a
+         * single NFS file system, if a local device number (st_dev) exceeds
+         * 255, or if a local inode number (st_ino) exceeds 16777215.
+         */
+        if (ENABLE_DESKTOP
+         && stb[0].st_ino == stb[1].st_ino
+         && stb[0].st_dev == stb[1].st_dev
+         && stb[0].st_size == stb[1].st_size
+         && stb[0].st_mtime == stb[1].st_mtime
+         && stb[0].st_ctime == stb[1].st_ctime
+         && stb[0].st_mode == stb[1].st_mode
+         && stb[0].st_nlink == stb[1].st_nlink
+         && stb[0].st_uid == stb[1].st_uid
+         && stb[0].st_gid == stb[1].st_gid
+        ) {
+                /* files are physically the same; no need to compare them */
+                return STATUS_SAME;
+        }
+
         if (S_ISDIR(stb[0].st_mode) && S_ISDIR(stb[1].st_mode)) {
 #if ENABLE_FEATURE_DIFF_DIR
                 diffdir(file, s_start);