Mercurial: The Definitive Guide

Third-Party Tools for Working with Patches

Once you’ve been working with patches for a while, you’ll find yourself hungry for tools that will help you to understand and manipulate the patches you’re dealing with.

The diffstat command generates a histogram of the modifications made to each file in a patch. It provides a good way to “get a sense of” a patch—which files it affects, and how much change it introduces to each file and as a whole. (I find that it’s a good idea to use diffstat’s -p option as a matter of course, as otherwise it will try to do clever things with prefixes of filenames that inevitably confuse at least me.)

$ diffstat -p1 remove-redundant-null-checks.patch
 drivers/char/agp/sgi-agp.c        |    5 ++---
 drivers/char/hvcs.c               |   11 +++++------
 drivers/message/fusion/mptfc.c    |    6 ++----
 drivers/message/fusion/mptsas.c   |    3 +--
 drivers/net/fs_enet/fs_enet-mii.c |    3 +--
 drivers/net/wireless/ipw2200.c    |   22 ++++++----------------
 drivers/scsi/libata-scsi.c        |    4 +---
 drivers/video/au1100fb.c          |    3 +--
 8 files changed, 19 insertions(+), 38 deletions(-)
$ filterdiff -i '*/video/*' remove-redundant-null-checks.patch
--- a/drivers/video/au1100fb.c~remove-redundant-null-checks-before-free-in-drivers
+++ a/drivers/video/au1100fb.c
@@ -743,8 +743,7 @@ void __exit au1100fb_cleanup(void)
 {
 	driver_unregister(&au1100fb_driver);
 
-	if (drv_info.opt_mode)
-		kfree(drv_info.opt_mode);
+	kfree(drv_info.opt_mode);
 }
 
 module_init(au1100fb_init);

The patchutils package is invaluable. It provides a set of small ...