Re: [PATCH 2/8] log: Only check for FALLOC_FL_COLLAPSE_RANGE availability at runtime

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Nov 06, 2024 at 08:10:41PM +0100, Stefano Brivio wrote:
> On Wed,  6 Nov 2024 17:54:15 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > log.c has several #ifdefs on FALLOC_FL_COLLAPSE_RANGE that won't attempt
> > to use it if not defined.  But even if the value is defined at compile
> > time, it might not be available in the runtime kernel, so we need to check
> > for errors from a fallocate() call and fall back to other methods.
> > 
> > Simplify this to only need the runtime check by using linux_dep.h to define
> > FALLOC_FL_COLLAPSE_RANGE if it's not in the kernel headers.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  Makefile    | 5 -----
> >  linux_dep.h | 6 ++++++
> >  log.c       | 9 +--------
> >  3 files changed, 7 insertions(+), 13 deletions(-)
> > 
> > diff --git a/Makefile b/Makefile
> > index 56bf2e8..cb91535 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -59,11 +59,6 @@ ifeq ($(shell :|$(CC) -fstack-protector-strong -S -xc - -o - >/dev/null 2>&1; ec
> >  	FLAGS += -fstack-protector-strong
> >  endif
> >  
> > -C := \#define _GNU_SOURCE\n\#include <fcntl.h>\nint x = FALLOC_FL_COLLAPSE_RANGE;
> > -ifeq ($(shell printf "$(C)" | $(CC) -S -xc - -o - >/dev/null 2>&1; echo $$?),0)
> > -	EXTRA_SYSCALLS += fallocate
> > -endif
> > -
> >  prefix		?= /usr/local
> >  exec_prefix	?= $(prefix)
> >  bindir		?= $(exec_prefix)/bin
> > diff --git a/linux_dep.h b/linux_dep.h
> > index 8921623..eae9c3c 100644
> > --- a/linux_dep.h
> > +++ b/linux_dep.h
> > @@ -119,4 +119,10 @@ struct tcp_info_linux {
> >  						 */
> >  };
> >  
> > +#include <linux/falloc.h>
> > +
> > +#ifndef FALLOC_FL_COLLAPSE_RANGE
> > +#define FALLOC_FL_COLLAPSE_RANGE	0x08
> > +#endif
> > +
> >  #endif /* LINUX_DEP_H */
> > diff --git a/log.c b/log.c
> > index 19f1d98..3c1b39c 100644
> > --- a/log.c
> > +++ b/log.c
> > @@ -92,7 +92,6 @@ const char *logfile_prefix[] = {
> >  	"         ",		/* LOG_DEBUG */
> >  };
> >  
> > -#ifdef FALLOC_FL_COLLAPSE_RANGE
> 
> This breaks the build on Alpine (and I suppose on Void Linux too, that
> is, whenever we build against musl):
> 
> log.c: In function 'logfile_rotate':
> log.c:207:28: error: 'FALLOC_FL_COLLAPSE_RANGE' undeclared (first use in this function)
>   207 |         if (!fallocate(fd, FALLOC_FL_COLLAPSE_RANGE, 0, log_cut_size))
>       |                            ^~~~~~~~~~~~~~~~~~~~~~~~
> log.c:207:28: note: each undeclared identifier is reported only once for each function it appears in
> 
> and it's fixed by including linux_dep.h from log.c.

Oops, that was careless.  Fixed for the next spin.

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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