Re: [PATCH] util/compatfd.c: use libc signalfd wrapper instead of raw syscall

[Paolo Bonzini <pbonzini@redhat.com>]

On 05/09/21 03:16, Kacper Słomiński wrote:
> This allows the use of native signalfd instead of the sigtimedwait
> based emulation on systems other than Linux.
> 
> Signed-off-by: Kacper Słomiński <kacper.slominski72@gmail.com>
> ---
> Apologies if I CC'd the wrong maintaineers, it's my first time
> submitting patches to QEMU. According to get_maintainers.pl this
> file has no maintainers, and the only system supported upstream
> that supports signalfd natively is Linux.
> 
> Glibc has had the signalfd wrapper since version 2.8 (2008), and
> musl has had it since at least version 0.5.0 (2011), and as such
> I think using syscall directly is not necessary here.
> 
> Found this while porting QEMU to Managarm
> (https://github.com/managarm/managarm).
> 
>   meson.build     | 7 +++----
>   util/compatfd.c | 5 ++---
>   2 files changed, 5 insertions(+), 7 deletions(-)

Queued, thanks!

Paolo

> diff --git a/meson.build b/meson.build
> index bf63784812..bcdfea5492 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -1415,10 +1415,9 @@ config_host_data.set('CONFIG_POSIX_MADVISE', cc.links(gnu_source_prefix + '''
>     #include <stddef.h>
>     int main(void) { return posix_madvise(NULL, 0, POSIX_MADV_DONTNEED); }'''))
>   config_host_data.set('CONFIG_SIGNALFD', cc.links(gnu_source_prefix + '''
> -  #include <unistd.h>
> -  #include <sys/syscall.h>
> -  #include <signal.h>
> -  int main(void) { return syscall(SYS_signalfd, -1, NULL, _NSIG / 8); }'''))
> +  #include <sys/signalfd.h>
> +  #include <stddef.h>
> +  int main(void) { return signalfd(-1, NULL, SFD_CLOEXEC); }'''))
>   config_host_data.set('CONFIG_SPLICE', cc.links(gnu_source_prefix + '''
>     #include <unistd.h>
>     #include <fcntl.h>
> diff --git a/util/compatfd.c b/util/compatfd.c
> index a8ec525c6c..ab810c42a9 100644
> --- a/util/compatfd.c
> +++ b/util/compatfd.c
> @@ -17,7 +17,7 @@
>   #include "qemu/thread.h"
>   
>   #if defined(CONFIG_SIGNALFD)
> -#include <sys/syscall.h>
> +#include <sys/signalfd.h>
>   #endif
>   
>   struct sigfd_compat_info {
> @@ -96,9 +96,8 @@ 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
>