Re: [PATCH v2] grub-mount: Support libfuse 3

[Daniel Kiper]

On Mon, Jan 17, 2022 at 03:34:37PM +0100, Fabian Vogt wrote:
> libfuse 3.0.0 got released in 2016, with some API changes compared to 2.x.
> This commit introduces support for 3.x while keeping it compatible with 2.6
> as a fallback still.
>
> To detect fuse3, switch configure over to use pkg-config, which is simpler yet
> more reliable than looking for library and header manually. Also set
> FUSE_USE_VERSION that way, as it depends on the used libfuse version.
>
> Now that the CFLAGS are read from pkg-config, use just <fuse.h>, which works
> with 2.x as well as 3.x and is recommended by libfuse upstream.
>
> One behaviour change of libfuse3 is that FUSE_ATOMIC_O_TRUNC is set by 
> default,
> which means that open with O_TRUNC is passed as-is instead of calling the
> truncate operation. With libfuse2, truncate failed with -ENOSYS and that was
> returned to the application. To make O_TRUNC fail with libfuse3, return -EROFS
> explicitly if writing was requested.
>
> Signed-off-by: Fabian Vogt <fvogt@suse.de>

Sadly this patch breaks Windows builds:
  In file included from util/grub-mount.c:36:0:
  /usr/include/fuse/fuse.h:33:25: fatal error: sys/statvfs.h: No such file or 
directory
   #include <sys/statvfs.h>
                         ^
  compilation terminated.

I think it happens because pkg-config is not aware we want make Windows
version of the GRUB. So, I would suggest to disable FUSE detection when
the host for tools is Windows.

And two nits below...

> ---
> v2: add __attribute__ ((unused))
>
>  Makefile.util.def |  4 +++-
>  configure.ac      | 16 +++++-----------
>  util/grub-mount.c | 25 ++++++++++++++++++++++---
>  3 files changed, 30 insertions(+), 15 deletions(-)
>
> diff --git a/Makefile.util.def b/Makefile.util.def
> index f8b356cc1..e92c1f346 100644
> --- a/Makefile.util.def
> +++ b/Makefile.util.def
> @@ -309,11 +309,13 @@ program = {
>    common = grub-core/disk/host.c;
>    common = grub-core/osdep/init.c;
>
> +  cflags = '$(FUSE_CFLAGS)';
> +
>    ldadd = libgrubmods.a;
>    ldadd = libgrubgcry.a;
>    ldadd = libgrubkern.a;
>    ldadd = grub-core/lib/gnulib/libgnu.a;
> -  ldadd = '$(LIBINTL) $(LIBDEVMAPPER) $(LIBZFS) $(LIBNVPAIR) $(LIBGEOM) 
> -lfuse';
> +  ldadd = '$(LIBINTL) $(LIBDEVMAPPER) $(LIBZFS) $(LIBNVPAIR) $(LIBGEOM) 
> $(FUSE_LIBS)';
>    condition = COND_GRUB_MOUNT;
>  };
>
> diff --git a/configure.ac b/configure.ac
> index 4f649edaf..1d40f9560 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -1787,17 +1787,11 @@ if test x"$enable_grub_mount" = xno ; then
>  fi
>
>  if test x"$grub_mount_excuse" = x ; then
> -  AC_CHECK_LIB([fuse], [fuse_main_real], [],
> -               [grub_mount_excuse="need FUSE library"])
> -fi
> -
> -if test x"$grub_mount_excuse" = x ; then
> -  # Check for fuse headers.
> -  SAVED_CPPFLAGS="$CPPFLAGS"
> -  CPPFLAGS="$CPPFLAGS -DFUSE_USE_VERSION=26"
> -  AC_CHECK_HEADERS([fuse/fuse.h], [],
> -     [grub_mount_excuse=["need FUSE headers"]])
> -  CPPFLAGS="$SAVED_CPPFLAGS"
> +  PKG_CHECK_MODULES([FUSE], [fuse3], [FUSE_CFLAGS="$FUSE_CFLAGS 
> -DFUSE_USE_VERSION=32"], [

s/[FUSE]/[fuse3]/

> +    PKG_CHECK_MODULES([FUSE], [fuse], [FUSE_CFLAGS="$FUSE_CFLAGS 
> -DFUSE_USE_VERSION=26"], [

s/[FUSE]/[fuse]/

Otherwise you cannot differentiate FUSE3 and FUSE detection just reading the
configure messages.

Daniel