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Use pkg-config to discover libnl-3 #1637

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966d515
Use pkg-config to find libnl-3 headers
fpletz Mar 12, 2025
40dcb84
Dynamically load libnl-3 libs from pkg-config libdir
fpletz Mar 12, 2025
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11 changes: 8 additions & 3 deletions configure.ac
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Original file line number Diff line number Diff line change
Expand Up @@ -961,14 +961,16 @@ case "$enable_delayacct" in
enable_delayacct=no
else
old_CFLAGS="$CFLAGS"
CFLAGS="$CFLAGS -I/usr/include/libnl3"
htop_config_cflags=`$PKG_CONFIG --cflags libnl-3.0 2>/dev/null` || continue
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I wish some quality improvements to the check:

  1. There's no error handling here. What would you do if the pkg-config call fails?
  2. Is there any reason not to use PKG_CHECK_MODULES macro as in the old code?
  3. You should allow the user to override the compiler flags detected. If you have used PKG_CHECK_MODULES, then the variable LIBNL3_CFLAGS would be defined automatically to allow that user override. Otherwise, maybe you can define it yourself? (AC_ARG_VAR([LIBNL3_CFLAGS], [C compiler flags for libnl3, overriding pkg-config]))

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There's no error handling here. What would you do if the pkg-config call fails?

In this case the AC_CHECK_HEADERS fails like it would have done before since htop_config_cflags is empty and the headers aren't found. But PKG_CHECK_MODULES should take care of that.

Is there any reason not to use PKG_CHECK_MODULES macro as in the old code?

I used the current style since that is used to discover ncurses in the same file. I agree that PKG_CHECK_MODULES is the better solution and will change the code accordingly.

You should allow the user to override the compiler flags detected. If you have used PKG_CHECK_MODULES, then the variable LIBNL3_CFLAGS would be defined automatically to allow that user override. Otherwise, maybe you can define it yourself? (AC_ARG_VAR([LIBNL3_CFLAGS], [C compiler flags for libnl3, overriding pkg-config]))

Yes, makes sense. I will add this. And also introduce the variable LIBNL3_LIBDIR.

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The reason the ncurses detection code doesn't use PKG_CHECK_MODULES is that ncurses may come with many different library names (as well as .pc file names), so the code has to implement fallbacks.

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AFAICS, this should be || true, as there is no loop.

Suggested change
htop_config_cflags=`$PKG_CONFIG --cflags libnl-3.0 2>/dev/null` || continue
htop_config_cflags=`$PKG_CONFIG --cflags libnl-3.0 2>/dev/null` || true

CFLAGS="$CFLAGS $htop_config_cflags"
AC_CHECK_HEADERS([netlink/attr.h netlink/handlers.h netlink/msg.h], [enable_delayacct=yes], [enable_delayacct=no])
CFLAGS="$old_CFLAGS"
fi
;;
yes)
old_CFLAGS="$CFLAGS"
CFLAGS="$CFLAGS -I/usr/include/libnl3"
htop_config_cflags=`$PKG_CONFIG --cflags libnl-3.0 2>/dev/null` || continue
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Same here …

Suggested change
htop_config_cflags=`$PKG_CONFIG --cflags libnl-3.0 2>/dev/null` || continue
htop_config_cflags=`$PKG_CONFIG --cflags libnl-3.0 2>/dev/null` || true

CFLAGS="$CFLAGS $htop_config_cflags"
AC_CHECK_HEADERS([netlink/attr.h netlink/handlers.h netlink/msg.h], [], [AC_MSG_ERROR([can not find required header files netlink/attr.h, netlink/handlers.h, netlink/msg.h])])
CFLAGS="$old_CFLAGS"
;;
Expand All @@ -978,7 +980,10 @@ case "$enable_delayacct" in
esac
if test "$enable_delayacct" = yes; then
AC_DEFINE([HAVE_DELAYACCT], [1], [Define if delay accounting support should be enabled.])
AM_CFLAGS="$AM_CFLAGS -I/usr/include/libnl3"
htop_config_cflags=`$PKG_CONFIG --cflags libnl-3.0 2>/dev/null`
AM_CFLAGS="$AM_CFLAGS $htop_config_cflags"
libdir_libnl=`$PKG_CONFIG --variable=libdir libnl-3.0 2>/dev/null`
Comment on lines +983 to +985
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Failure to read these should result in a proper error message generated, or a warning notifying of a fallback to /usr/include being used.

AC_DEFINE_UNQUOTED([LIBDIR_LIBNL], ["$libdir_libnl"], [Path to the libnl-3 libraries])
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Um. A small question (maybe this is bike shedding).
Which name for the shell variable / C macro is better, LIBNL_LIBDIR or LIBDIR_LIBNL?

I would vote for LIBNL_LIBDIR.

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Other places like for hwloc use FOO_LIBS, thus LIBNL_LIBDIR would be reasonable.

fi
AM_CONDITIONAL([HAVE_DELAYACCT], [test "$enable_delayacct" = yes])

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8 changes: 4 additions & 4 deletions linux/LibNl.c
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Original file line number Diff line number Diff line change
Expand Up @@ -78,17 +78,17 @@ static int load_libnl(void) {
if (libnlHandle && libnlGenlHandle)
return 0;

libnlHandle = dlopen("libnl-3.so", RTLD_LAZY);
libnlHandle = dlopen(LIBDIR_LIBNL "/libnl-3.so", RTLD_LAZY);
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I noticed a slash is used here unconditionally. Normally for libraries it's better to load them from default search paths rather than forcing a directory prefix at compile time. I know the directory is grabbed from pkg-config with this patch, but what if no directory prefix is specified there?

if (!libnlHandle) {
libnlHandle = dlopen("libnl-3.so.200", RTLD_LAZY);
libnlHandle = dlopen(LIBDIR_LIBNL "/libnl-3.so.200", RTLD_LAZY);
if (!libnlHandle) {
goto dlfailure;
}
}

libnlGenlHandle = dlopen("libnl-genl-3.so", RTLD_LAZY);
libnlGenlHandle = dlopen(LIBDIR_LIBNL "/libnl-genl-3.so", RTLD_LAZY);
if (!libnlGenlHandle) {
libnlGenlHandle = dlopen("libnl-genl-3.so.200", RTLD_LAZY);
libnlGenlHandle = dlopen(LIBDIR_LIBNL "/libnl-genl-3.so.200", RTLD_LAZY);
if (!libnlGenlHandle) {
goto dlfailure;
}
Expand Down