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



Daniel P. Berrange wrote:
> 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 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.

An alternative is to use something like the hard-coded list in
coreutils' src/stat.c (from which src/fs.h is generated).

  http://git.savannah.gnu.org/cgit/coreutils.git/tree/src/stat.c#n219

It is a list of all known (to me) FS magic numbers, and src/Makefile.am
includes a couple of checks that give us a chance of spotting new
additions.


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