linux-kernel - Re: [PATCH][trace-cmd] blk plugin: replace BLK_TC_BARRIER with BLK_TC_FLUSH/BLK_TC

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Date:	Mon, 9 Jan 2012 11:11:28 +0000
From:	Stefan Hajnoczi <stefanha@...ux.vnet.ibm.com>
To:	Namhyung Kim <namhyung@...il.com>
Cc:	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH][trace-cmd] blk plugin: replace BLK_TC_BARRIER with
 BLK_TC_FLUSH/BLK_TC_FUA

On Mon, Jan 09, 2012 at 01:27:12AM +0900, Namhyung Kim wrote:
> Stefan Hajnoczi <stefanha@...ux.vnet.ibm.com> wrote:
> 
> > The BLK_TC_BARRIER flag was dropped in Linux commit c09c47caedc in
> > August 2011.  The blk plugin fails to build against recent kernel
> > headers.  Since no flag bits were left, the new BLK_TC_FLUSH flag reused
> > the BLK_TC_BARRIER bit.  The new BLK_TC_FUA flag was also added.
> >
> > This patch updates fill_rwbs() to reflect the new
> > BLK_TC_FLUSH/BLK_TC_FUA flags.  This allows plugin_blk.c to build
> > successfully on recent kernels.  The drawback is that this breaks the
> > build for pre-c09c47caedc kernel headers.
> >
> > Signed-off-by: Stefan Hajnoczi <stefanha@...ux.vnet.ibm.com>
> > ---
> > There is an alternative version of this patch with a build test in the Makefile
> > so that we know whether to use BLK_TC_BARRIER or BLK_TC_FLUSH/BLK_TC_FUA.  That
> > would support both old and new kernel headers using a HAVE_BLK_TC_FLUSH #ifdef.
> >
> > I wasn't able to find the right makefile shell escaping magic to get the
> > build-test function to work.  If anyone knows how to test a snippet like the
> > following, then that would be nicer:
> >
> >   #include <linux/blktrace_api.h>
> >   int main(void) { return BLK_TC_FLUSH; }
> >
> 
> Hi,
> 
> The perf uses following code for that:
> 
> # try-cc
> # Usage: option = $(call try-cc, source-to-build, cc-options)
> try-cc = $(shell sh -c						  \
> 	'TMP="$(OUTPUT)$(TMPOUT).$$$$";				  \
> 	 echo "$(1)" |						  \
> 	 $(CC) -x c - $(2) -o "$$TMP" > /dev/null 2>&1 && echo y; \
> 	 rm -f "$$TMP"')

Looks perfect, thanks!

Stefan

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