[Qemu-devel] [PATCH 0/2] clean up SYS_signalfd

[Qemu-devel] [PATCH 0/2] clean up SYS_signalfd

[Laszlo Ersek]

SYS_signalfd is deprecated and absent on some Linux systems that do
support signalfd().

Also, in 2015 the signalfd() libc function should be available wherever
the underlying syscall(s) are available.

Drop SYS_signalfd and check for & use signalfd() directly.

Laszlo Ersek (2):
  qemu_signalfd_available(): remove function due to lack of callers
  signalfd(): modernize detection and use

 configure               | 11 ++++++++---
 include/qemu/compatfd.h |  1 -
 util/compatfd.c         | 24 ++----------------------
 3 files changed, 10 insertions(+), 26 deletions(-)

-- 
1.8.3.1

[Qemu-devel] [PATCH 1/2] qemu_signalfd_available(): remove function due to lack of callers

[Laszlo Ersek]

Noone calls qemu_signalfd_available(), let's remove it.

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 include/qemu/compatfd.h |  1 -
 util/compatfd.c         | 19 -------------------
 2 files changed, 20 deletions(-)

diff --git a/include/qemu/compatfd.h b/include/qemu/compatfd.h
index 6b04877..fc37915 100644
--- a/include/qemu/compatfd.h
+++ b/include/qemu/compatfd.h
@@ -39,6 +39,5 @@ struct qemu_signalfd_siginfo {
 };
 
 int qemu_signalfd(const sigset_t *mask);
-bool qemu_signalfd_available(void);
 
 #endif
diff --git a/util/compatfd.c b/util/compatfd.c
index 341ada6..e857150 100644
--- a/util/compatfd.c
+++ b/util/compatfd.c
@@ -108,22 +108,3 @@ int qemu_signalfd(const sigset_t *mask)
 
     return qemu_signalfd_compat(mask);
 }
-
-bool qemu_signalfd_available(void)
-{
-#ifdef CONFIG_SIGNALFD
-    sigset_t mask;
-    int fd;
-    bool ok;
-    sigemptyset(&mask);
-    errno = 0;
-    fd = syscall(SYS_signalfd, -1, &mask, _NSIG / 8);
-    ok = (errno != ENOSYS);
-    if (fd >= 0) {
-        close(fd);
-    }
-    return ok;
-#else
-    return false;
-#endif
-}
-- 
1.8.3.1

[Qemu-devel] [PATCH 2/2] signalfd(): modernize detection and use

[Laszlo Ersek]

qemu_signalfd() provides the (effects of the) Linux signalfd() syscall on
platforms that lack it. However, the check for the availability of
signalfd() in configure, and its use in qemu_signalfd() when it *is*
available, are seriously outdated (they date back to 2010-2011).

To wit, the SYS_signalfd-based check in configure can actually fail on at
least modern aarch64 Linux systems that *do* have signalfd().
(SYS_signalfd is deprecated and has been replaced by SYS_signalfd4 (note
the "4"). The signalfd() libc function selects the appropriate system
call.)

We should consider signalfd() accessible as a first class libc function on
platforms that support it. Modernize the related parts in configure and
"util/compatfd.c" (so that we end up with something similar to eventfd()'s
detection).

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 configure       | 11 ++++++++---
 util/compatfd.c |  5 ++---
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/configure b/configure
index 5ea1014..de0d21c 100755
--- a/configure
+++ b/configure
@@ -3280,10 +3280,15 @@ fi
 # signalfd probe
 signalfd="no"
 cat > $TMPC << EOF
-#include <unistd.h>
-#include <sys/syscall.h>
+#include <sys/signalfd.h>
 #include <signal.h>
-int main(void) { return syscall(SYS_signalfd, -1, NULL, _NSIG / 8); }
+int main(void)
+{
+    sigset_t s;
+
+    sigfillset(&s);
+    return signalfd(-1, &s, SFD_CLOEXEC);
+}
 EOF
 
 if compile_prog "" "" ; then
diff --git a/util/compatfd.c b/util/compatfd.c
index e857150..7983391 100644
--- a/util/compatfd.c
+++ b/util/compatfd.c
@@ -17,7 +17,7 @@
 #include "qemu/compatfd.h"
 #include "qemu/thread.h"
 
-#include <sys/syscall.h>
+#include <sys/signalfd.h>
 
 struct sigfd_compat_info
 {
@@ -99,9 +99,8 @@ int qemu_signalfd(const sigset_t *mask)
 #if defined(CONFIG_SIGNALFD)
     int ret;
 
-    ret = syscall(SYS_signalfd, -1, mask, _NSIG / 8);
+    ret = signalfd(-1, mask, SFD_CLOEXEC);
     if (ret != -1) {
-        qemu_set_cloexec(ret);
         return ret;
     }
 #endif
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH 0/2] clean up SYS_signalfd

[Paolo Bonzini]

On 21/01/2015 13:57, Laszlo Ersek wrote:
> SYS_signalfd is deprecated and absent on some Linux systems that do
> support signalfd().
> 
> Also, in 2015 the signalfd() libc function should be available wherever
> the underlying syscall(s) are available.
> 
> Drop SYS_signalfd and check for & use signalfd() directly.
> 
> Laszlo Ersek (2):
>   qemu_signalfd_available(): remove function due to lack of callers
>   signalfd(): modernize detection and use
> 
>  configure               | 11 ++++++++---
>  include/qemu/compatfd.h |  1 -
>  util/compatfd.c         | 24 ++----------------------
>  3 files changed, 10 insertions(+), 26 deletions(-)

I suspect this will stop using signalfd on RHEL5.  I wouldn't weep, but
it's worth pointing it out.

Paolo