[PATCH] meson: improve CPU affinity routines check

[Roman Bogorodskiy]

  Martin Kletzander wrote:

> On Sun, Nov 21, 2021 at 07:58:55PM +0400, Roman Bogorodskiy wrote:
> >Recently, FreeBSD has got sched_get/setaffinity(3) implementations and
> >the sched.h header as well [1]. To make these routines visible,
> >users have to define _WITH_CPU_SET_T.
> >
> >This breaks current detection. Specifically, meson sees the
> >sched_getaffinity() symbol and defines WITH_SCHED_GETAFFINITY. This
> >define unlocks Linux implementation of virProcessSetAffinity() and other
> >functions, which fails to build on FreeBSD because cpu_set_t is not
> >visible as _WITH_CPU_SET_T is not defined.
> >
> >For now, change detection to the following:
> >
> > - Instead of checking sched_getaffinity(), check if 'cpu_set_t' is
> >   available through sched.h
> > - Explicitly check the sched.h header instead of assuming its presence
> >   if WITH_SCHED_SETSCHEDULER is defined
> >
> 
> Makes sense, although even the sched_getaffinity() is guarded by the new
> _WITH_CPU_SET_T so there should be no error with the current code, am I

Nope, as I tried to explain in the commit message, the current code is
not working properly as it's using cc.has_function() for 'sched_getaffinity'
and this check passes because it's checking the specified function in
the standard library, so it works regardless of _WITH_CPU_SET_T. And as
it finds the sched_getaffinity(), the build still fails because we don't
set _WITH_CPU_SET_T.

> right?  And if I understand correctly we cannot use the FreeBSD
> implementation as is because they do not have all the CPU_* macros we
> need, right?

Frankly speaking, I haven't yet tested this implementation. Currently,
virprocess.c is using the original FreeBSD interface: cpuset_(get|set)affinity.
Generally, it would be a good thing to use the same implementation for
both Linux and FreeBSD, however, this Linux-compatible interface in
FreeBSD is not yet available in any FreeBSD release, so we'll have to keep
the old code for some time anyway, and also I need to test if it
actually works for us and figure out how to better detect and pass this _WITH_CPU_SET_T
with meson.

> >1:
> >https://cgit.freebsd.org/src/commit/?id=43736b71dd051212d5c55be9fa21c45993017fbb
> >https://cgit.freebsd.org/src/commit/?id=160b4b922b6021848b6b48afc894d16b879b7af2
> >https://cgit.freebsd.org/src/commit/?id=90fa9705d5cd29cf11c5dc7319299788dec2546a
> >
> >Signed-off-by: Roman Bogorodskiy <bogorodskiy at gmail.com>
> >---
> > meson.build           | 4 +++-
> > src/util/virprocess.c | 8 ++++----
> > 2 files changed, 7 insertions(+), 5 deletions(-)
> >
> >diff --git a/meson.build b/meson.build
> >index 9022bcfdc9..e4f36e8574 100644
> >--- a/meson.build
> >+++ b/meson.build
> >@@ -553,7 +553,6 @@ functions = [
> >   'posix_fallocate',
> >   'posix_memalign',
> >   'prlimit',
> >-  'sched_getaffinity',
> >   'sched_setscheduler',
> >   'setgroups',
> >   'setns',
> >@@ -602,6 +601,7 @@ headers = [
> >   'net/if.h',
> >   'pty.h',
> >   'pwd.h',
> >+  'sched.h',
> >   'sys/auxv.h',
> >   'sys/ioctl.h',
> >   'sys/mount.h',
> >@@ -671,6 +671,8 @@ symbols = [
> >
> >   # Check for BSD approach for setting MAC addr
> >   [ 'net/if_dl.h', 'link_addr', '#include <sys/types.h>\n#include <sys/socket.h>' ],
> >+
> >+  [ 'sched.h', 'cpu_set_t' ],
> > ]
> >
> > if host_machine.system() == 'linux'
> >diff --git a/src/util/virprocess.c b/src/util/virprocess.c
> >index 6de3f36f52..81de90200e 100644
> >--- a/src/util/virprocess.c
> >+++ b/src/util/virprocess.c
> >@@ -35,7 +35,7 @@
> > # include <sys/time.h>
> > # include <sys/resource.h>
> > #endif
> >-#if WITH_SCHED_SETSCHEDULER
> >+#if WITH_SCHED_H
> > # include <sched.h>
> > #endif
> >
> >@@ -480,7 +480,7 @@ int virProcessKillPainfully(pid_t pid, bool force)
> >     return virProcessKillPainfullyDelay(pid, force, 0, false);
> > }
> >
> >-#if WITH_SCHED_GETAFFINITY
> >+#if WITH_DECL_CPU_SET_T
> >
> > int virProcessSetAffinity(pid_t pid, virBitmap *map, bool quiet)
> > {
> >@@ -626,7 +626,7 @@ virProcessGetAffinity(pid_t pid)
> >     return ret;
> > }
> >
> >-#else /* WITH_SCHED_GETAFFINITY */
> >+#else /* WITH_DECL_CPU_SET_T */
> >
> > int virProcessSetAffinity(pid_t pid G_GNUC_UNUSED,
> >                           virBitmap *map G_GNUC_UNUSED,
> >@@ -646,7 +646,7 @@ virProcessGetAffinity(pid_t pid G_GNUC_UNUSED)
> >                          _("Process CPU affinity is not supported on this platform"));
> >     return NULL;
> > }
> >-#endif /* WITH_SCHED_GETAFFINITY */
> >+#endif /* WITH_DECL_CPU_SET_T */
> >
> >
> > int virProcessGetPids(pid_t pid, size_t *npids, pid_t **pids)
> >-- 
> >2.33.1
> >



Roman Bogorodskiy
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