[git commit master 1/1] diff: optimize diffing of files with the same metadata

[Denys Vlasenko]

commit: http://git.busybox.net/busybox/commit/?id=95f5c52e6f823c710be807fb86c8b2fafec8a334
branch: http://git.busybox.net/busybox/commit/?id=refs/heads/master

Signed-off-by: Roman Borisov <ext-roman.borisov at nokia.com>
Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 editors/diff.c |   25 +++++++++++++++++++++++++
 1 files changed, 25 insertions(+), 0 deletions(-)

diff --git a/editors/diff.c b/editors/diff.c
index ca4a4ea..3719bb4 100644
--- a/editors/diff.c
+++ b/editors/diff.c
@@ -952,6 +952,31 @@ 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);
-- 
1.7.3.4