Prior to 2a4b472c3c, sys/signal.h was only included on OpenBSD
(apart from two .c files). The POSIX standard location for this
header is just <signal.h> and in fact, OpenBSD's signal.h includes
sys/signal.h itself.

Unconditionally including <sys/signal.h> on musl causes warnings
for just about every source file:

  /usr/include/sys/signal.h:1:2: warning: #warning redirecting incorrect #include <sys/signal.h> to <signal.h> [-Wcpp]
      1 | #warning redirecting incorrect #include <sys/signal.h> to <signal.h>
        |  ^~~~~~~

Since there don't seem to be any platforms which require including
<sys/signal.h> in addition to <signal.h>, and some platforms like
Haiku lack it completely, just remove it.

Tested building on OpenBSD after removing this include.

Signed-off-by: Michael Forney <mforney@mforney.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
Changes since v1: rebase on latest master

 include/qemu/osdep.h | 4 ----
 meson.build          | 1 -
 2 files changed, 5 deletions(-)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index f9ec8c84e9..a434382c58 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -104,10 +104,6 @@ extern int daemon(int, int);
 #include <setjmp.h>
 #include <signal.h>
 
-#ifdef HAVE_SYS_SIGNAL_H
-#include <sys/signal.h>
-#endif
-
 #ifndef _WIN32
 #include <sys/wait.h>
 #else
diff --git a/meson.build b/meson.build
index 3d889857a0..af2bc89741 100644
--- a/meson.build
+++ b/meson.build
@@ -1113,7 +1113,6 @@ config_host_data.set('HAVE_DRM_H', cc.has_header('libdrm/drm.h'))
 config_host_data.set('HAVE_PTY_H', cc.has_header('pty.h'))
 config_host_data.set('HAVE_SYS_IOCCOM_H', cc.has_header('sys/ioccom.h'))
 config_host_data.set('HAVE_SYS_KCOV_H', cc.has_header('sys/kcov.h'))
-config_host_data.set('HAVE_SYS_SIGNAL_H', cc.has_header('sys/signal.h'))
 
 ignored = ['CONFIG_QEMU_INTERP_PREFIX'] # actually per-target
 arrays = ['CONFIG_AUDIO_DRIVERS', 'CONFIG_BDRV_RW_WHITELIST', 'CONFIG_BDRV_RO_WHITELIST']
-- 
2.30.0

On 1/13/21 4:56 PM, Michael Forney wrote:
> Prior to 2a4b472c3c, sys/signal.h was only included on OpenBSD
> (apart from two .c files). The POSIX standard location for this
> header is just <signal.h> and in fact, OpenBSD's signal.h includes
> sys/signal.h itself.
> 
> Unconditionally including <sys/signal.h> on musl causes warnings
> for just about every source file:
> 
>    /usr/include/sys/signal.h:1:2: warning: #warning redirecting incorrect #include <sys/signal.h> to <signal.h> [-Wcpp]
>        1 | #warning redirecting incorrect #include <sys/signal.h> to <signal.h>
>          |  ^~~~~~~
> 
> Since there don't seem to be any platforms which require including
> <sys/signal.h> in addition to <signal.h>, and some platforms like
> Haiku lack it completely, just remove it.
> 
> Tested building on OpenBSD after removing this include.
> 
> Signed-off-by: Michael Forney <mforney@mforney.org>
> Reviewed-by: Eric Blake <eblake@redhat.com>

I ran into this myself when testing an Alpine linux build with musl.

Seems to certainly cut down on the number of errors seen when building 
in Alpine. There's still a few more, but there's definitely less.

Tested-by: John Snow <jsnow@redhat.com>

On 13/01/2021 22.56, Michael Forney wrote:
> Prior to 2a4b472c3c, sys/signal.h was only included on OpenBSD
> (apart from two .c files). The POSIX standard location for this
> header is just <signal.h> and in fact, OpenBSD's signal.h includes
> sys/signal.h itself.
> 
> Unconditionally including <sys/signal.h> on musl causes warnings
> for just about every source file:
> 
>    /usr/include/sys/signal.h:1:2: warning: #warning redirecting incorrect #include <sys/signal.h> to <signal.h> [-Wcpp]
>        1 | #warning redirecting incorrect #include <sys/signal.h> to <signal.h>
>          |  ^~~~~~~
> 
> Since there don't seem to be any platforms which require including
> <sys/signal.h> in addition to <signal.h>, and some platforms like
> Haiku lack it completely, just remove it.
> 
> Tested building on OpenBSD after removing this include.
> 
> Signed-off-by: Michael Forney <mforney@mforney.org>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
> Changes since v1: rebase on latest master
> 
>   include/qemu/osdep.h | 4 ----
>   meson.build          | 1 -
>   2 files changed, 5 deletions(-)
> 
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index f9ec8c84e9..a434382c58 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -104,10 +104,6 @@ extern int daemon(int, int);
>   #include <setjmp.h>
>   #include <signal.h>
>   
> -#ifdef HAVE_SYS_SIGNAL_H
> -#include <sys/signal.h>
> -#endif
> -
>   #ifndef _WIN32
>   #include <sys/wait.h>
>   #else
> diff --git a/meson.build b/meson.build
> index 3d889857a0..af2bc89741 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -1113,7 +1113,6 @@ config_host_data.set('HAVE_DRM_H', cc.has_header('libdrm/drm.h'))
>   config_host_data.set('HAVE_PTY_H', cc.has_header('pty.h'))
>   config_host_data.set('HAVE_SYS_IOCCOM_H', cc.has_header('sys/ioccom.h'))
>   config_host_data.set('HAVE_SYS_KCOV_H', cc.has_header('sys/kcov.h'))
> -config_host_data.set('HAVE_SYS_SIGNAL_H', cc.has_header('sys/signal.h'))
>   
>   ignored = ['CONFIG_QEMU_INTERP_PREFIX'] # actually per-target
>   arrays = ['CONFIG_AUDIO_DRIVERS', 'CONFIG_BDRV_RW_WHITELIST', 'CONFIG_BDRV_RO_WHITELIST']
> 

Reviewed-by: Thomas Huth <thuth@redhat.com>