[libvirt] [PATCH] build: avoid compile failure on linux kernels older than 2.6.19

[Daniel P. Berrange]

On Mon, May 17, 2010 at 04:59:51PM +0200, Jim Meyering wrote:
> Daniel P. Berrange wrote:
> > On Mon, May 17, 2010 at 04:25:43PM +0200, Jim Meyering wrote:
> >> This is required for any kernel prior to 2.6.19,
> >> since <linux/magic.h> didn't exist back then.
> >> Now that file is provided by the kernel-headers package.
> >>
> >> >From d14ef1669968ffeb65076b007e318934ed99aa61 Mon Sep 17 00:00:00 2001
> >> From: Jim Meyering <meyering at redhat.com>
> >> Date: Mon, 17 May 2010 16:17:08 +0200
> >> Subject: [PATCH] build: avoid compile failure on linux kernels older than 2.6.19
> >>
> >> * configure.ac: Check for <linux/magic.h>.
> >> * src/util/storage_file.c: Include <linux/magic.h> only if present.
> >> Linux kernels prior to 2.6.19 lacked it.
> >> [__linux__] (NFS_SUPER_MAGIC): Define if not already defined.
> >> ---
> >>  configure.ac            |    2 +-
> >>  src/util/storage_file.c |    7 ++++++-
> >>  2 files changed, 7 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/configure.ac b/configure.ac
> >> index c187420..ebd2082 100644
> >> --- a/configure.ac
> >> +++ b/configure.ac
> >> @@ -108,7 +108,7 @@ LIBS=$old_libs
> >>
> >>  dnl Availability of various common headers (non-fatal if missing).
> >>  AC_CHECK_HEADERS([pwd.h paths.h regex.h sys/syslimits.h \
> >> -  termios.h sys/poll.h syslog.h mntent.h net/ethernet.h])
> >> +  termios.h sys/poll.h syslog.h mntent.h net/ethernet.h linux/magic.h])
> >>
> >>  dnl Where are the XDR functions?
> >>  dnl If portablexdr is installed, prefer that.
> >> diff --git a/src/util/storage_file.c b/src/util/storage_file.c
> >> index 5f15a64..a07bedc 100644
> >> --- a/src/util/storage_file.c
> >> +++ b/src/util/storage_file.c
> >> @@ -27,7 +27,9 @@
> >>  #include <unistd.h>
> >>  #include <fcntl.h>
> >>  #ifdef __linux__
> >> -# include <linux/magic.h>
> >> +# if HAVE_LINUX_MAGIC_H
> >> +#  include <linux/magic.h>
> >> +# endif
> >
> > Don't bother with this - just kill this include off completely. It is a
> > waste of time using it if we can't rely on it existing & have to re-define
> > everything ourselves.
> 
> I admit that those numbers will probably never change, but I see
> including the recommended/modern header as the preferred approach.
> Then, eventually when the old systems are no longer relevant (yeah, in
> a long time) we'll be able to remove our hackish define-if-required code.

If we're going to plan todo that then we need to open a  bug report against
the current linux/magic.h because it is still missing many filesystems that 
exist today.

Daniel
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