[Buildroot] [PATCH 3/9] linux: meddle not in the affairs of filesystems, for you are tasty with bacon

[Yann E. MORIN <yann.morin.1998@free.fr>]

Thomas, All,

On 2015-10-01 08:20 +0200, Thomas Petazzoni spake thusly:
> On Wed, 30 Sep 2015 23:54:46 +0200, Yann E. MORIN wrote:
> > Currently, the rule to rebuild the Linux kernel with an initramfs
> > directly depends on the filesystem image filename.
> > 
> > This is inherently "bad" from a purity point of view. linux.mk should
> > not have to delve into the fs internals.
> > 
> > Rather, make it directly depend on the "frontal" rule that generates the
> > cpio image.
> > 
> > Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
> > Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> > Cc: Arnout Vandecappelle <arnout@mind.be>
> > 
> > ---
> > This, too, will be useful for the initramfs patch coming next.
> > ---
> >  linux/linux.mk | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/linux/linux.mk b/linux/linux.mk
> > index 316f973..864ccbf 100644
> > --- a/linux/linux.mk
> > +++ b/linux/linux.mk
> > @@ -392,7 +392,7 @@ $(eval $(kconfig-package))
> >  # been generated in $(BINARIES_DIR)/rootfs.cpio.
> >  $(LINUX_DIR)/.stamp_initramfs_rebuilt: $(LINUX_DIR)/.stamp_target_installed
> >  $(LINUX_DIR)/.stamp_initramfs_rebuilt: $(LINUX_DIR)/.stamp_images_installed
> > -$(LINUX_DIR)/.stamp_initramfs_rebuilt: $(BINARIES_DIR)/rootfs.cpio
> > +$(LINUX_DIR)/.stamp_initramfs_rebuilt: rootfs-cpio
> 
> Are you sure this is OK ? It creates a dependency of a "real target" on
> a "phony target", which means that the "real target" will *always* be
> rebuilt, at every invocation of "make". Is this what we want?

Well, that's alredy the behaviour we have: we always rebuild the images
on each make invocation. This patch does not change the current behaviour.

And indeed, that's what we do want. For the simple reason that he user
may manually change the content of target/ and re-run make to update the
images.

And anyway, the filesystem image files are already depending on a PHONY
target, and thus are always rebuilt:

    fs/common.mk:
      73 $$(BINARIES_DIR)/rootfs.$(1): target-finalize $$(ROOTFS_$(2)_DEPENDENCIES)

However, you are right that the dependency of a rule target onto a PHONY
target is not clean. And in fact, there is not reason for the stamp-file
to begin with. We can coalesce the recipe of the stamp-file into the
PHONY linux-rebuild-with-initramfs rule.

I'll update the patch to drop the stamp-file, unless you can come up
with a reason for its existence. ;-)

Regards,
Yann E. MORIN.

-- 
.-----------------.--------------------.------------------.--------------------.
|  Yann E. MORIN  | Real-Time Embedded | /"\ ASCII RIBBON | Erics' conspiracy: |
| +33 662 376 056 | Software  Designer | \ / CAMPAIGN     |  ___               |
| +33 223 225 172 `------------.-------:  X  AGAINST      |  \e/  There is no  |
| http://ymorin.is-a-geek.org/ | _/*\_ | / \ HTML MAIL    |   v   conspiracy.  |
'------------------------------^-------^------------------^--------------------'