Jakub Kicinski 2b7ac0c87d tools: ynl-gen: don't touch the output file if content is the same
I often regenerate all YNL files in the tree to make sure they
are in sync with the codegen and specs. Generator rewrites
the files unconditionally, so since make looks at file modification
time to decide what to rebuild - my next build takes longer.

We already generate the code to a tempfile most of the time,
only overwrite the target when we have to.

Before:

  $ stat include/uapi/linux/netdev.h
    File: include/uapi/linux/netdev.h
    Size: 2307      	Blocks: 8          IO Block: 4096   regular file
  Access: 2023-10-27 15:19:56.347071940 -0700
  Modify: 2023-10-27 15:19:45.089000900 -0700
  Change: 2023-10-27 15:19:45.089000900 -0700
   Birth: 2023-10-27 15:19:45.088000894 -0700

  $ ./tools/net/ynl/ynl-regen.sh -f
  [...]

  $ stat include/uapi/linux/netdev.h
    File: include/uapi/linux/netdev.h
    Size: 2307      	Blocks: 8          IO Block: 4096   regular file
  Access: 2023-10-27 15:19:56.347071940 -0700
  Modify: 2023-10-27 15:22:18.417968446 -0700
  Change: 2023-10-27 15:22:18.417968446 -0700
   Birth: 2023-10-27 15:19:45.088000894 -0700

After:

  $ stat include/uapi/linux/netdev.h
    File: include/uapi/linux/netdev.h
    Size: 2307      	Blocks: 8          IO Block: 4096   regular file
  Access: 2023-10-27 15:22:41.520114221 -0700
  Modify: 2023-10-27 15:22:18.417968446 -0700
  Change: 2023-10-27 15:22:18.417968446 -0700
   Birth: 2023-10-27 15:19:45.088000894 -0700

  $ ./tools/net/ynl/ynl-regen.sh -f
  [...]

  $ stat include/uapi/linux/netdev.h
    File: include/uapi/linux/netdev.h
    Size: 2307      	Blocks: 8          IO Block: 4096   regular file
  Access: 2023-10-27 15:22:41.520114221 -0700
  Modify: 2023-10-27 15:22:18.417968446 -0700
  Change: 2023-10-27 15:22:18.417968446 -0700
   Birth: 2023-10-27 15:19:45.088000894 -0700

Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20231027223408.1865704-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2023-11-01 22:14:00 -07:00
2022-09-28 09:02:20 +02:00
…
…
…

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.
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