[libvirt] [PATCH 1/2] cgroup: fix including sys/mount.h for OpenBSD

[Martin Kletzander]

On Sun, Jan 10, 2016 at 11:29:47PM +0300, Roman Bogorodskiy wrote:
>  Martin Kletzander wrote:
>
>> On Fri, Jan 08, 2016 at 10:36:07PM +0300, Roman Bogorodskiy wrote:
>> >From: Jasper Lievisse Adriaanse <jasper at openbsd.org>
>> >
>> >Include sys/param.h along with sys/mount.h to fix compilation on
>> >OpenBSD.
>> >
>> >Signed-off-by: Roman Bogorodskiy <bogorodskiy at gmail.com>
>> >---
>> > src/util/vircgroup.c | 3 ++-
>> > 1 file changed, 2 insertions(+), 1 deletion(-)
>> >
>> >diff --git a/src/util/vircgroup.c b/src/util/vircgroup.c
>> >index e39c4d1..e8e0875 100644
>> >--- a/src/util/vircgroup.c
>> >+++ b/src/util/vircgroup.c
>> >@@ -27,7 +27,8 @@
>> > #if defined HAVE_MNTENT_H && defined HAVE_GETMNTENT_R
>> > # include <mntent.h>
>> > #endif
>> >-#if defined HAVE_SYS_MOUNT_H
>> >+#if defined HAVE_SYS_PARAM_H && defined HAVE_SYS_MOUNT_H
>> >+# include <sys/param.h>
>> > # include <sys/mount.h>
>>
>> Wouldn't this cause an error for systems that have sys/mount.h and need
>> it for the mount() call, but don't have sys/param.h ?
>
>That's an interesting question.
>
>A check for sys/mount.h was added with the initial implementation of the
>mount() using code in commit 1da631e. The mount() call currently is used
>only on platforms with cgroups available (i.e. Linux).
>
>Moreover, HAVE_SYS_MOUNT_H does not play any role in cgroups detection:
>
>#if defined(__linux__) && defined(HAVE_GETMNTENT_R) && \
>    defined(_DIRENT_HAVE_D_TYPE) && defined(_SC_CLK_TCK)
># define VIR_CGROUP_SUPPORTED
>#endif
>
>So, sys/mount.h and mount() are only needed on Linux anyway, and I'm
>wondering if we actually can just do something like this:
>
>#if defined HAVE_SYS_MOUNT_H && defined HAVE_GETMNTENT_R
># include <sys/mount.h>
>#endif
>
>as if we don't have HAVE_GETMNTENT_R define, we will not have
>VIR_CGROUP_SUPPORTED, and therefore we'll not need the mount() call.
>

That's true.  While modifying this in my local tree I took it a little
bit further in my head.  First I thought why don't we include the header
just above the VIR_CGROUP_SUPPORTED definition.  Then I thought, hy why
don't we include everything that we can there (just to get rid of future
mistakes like this one with mount).  And then I figured that we could
split those two cgroup "implementations"

>I've tested it on FreeBSD and OpenBSD and it builds fine. Unfortunately,
>cannot test it on Linux at this moment.
>

Moreove the mount() calls that are there are only used for LXC.  Anyway,
I tested both your approach and also including the file only around the
definition of VIR_CGROUP_SUPPORTED (guarded with the HAVE_SYS_MOUNT_H of
course) and it worked.  But I wonder why we chose to implement cgroups
in one file and not split it into two so that we don't have to deal with
include issues if building without cgroups.  Having said that, I don't
know what's the preferred way, but now it looks like splitting into
multiple files (instead of #ifdef guarding) seems better, at least to me.

>Roman Bogorodskiy
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