misc: add syscall fallback for close_range for musl libc

Add fallback for the close_range syscall wrapper. This is needed for
musl libc, which currently does not have a close_range wrapper.

Also set errno on errors.

meson.build

@@ -197,6 +197,8 @@ endif
 
 if cc.has_function('close_range', prefix: '#define _GNU_SOURCE\n#include <unistd.h>')
   add_project_arguments('-DHAVE_CLOSE_RANGE', language: 'c')
+elif cc.has_header('linux/close_range.h')
+  add_project_arguments('-DHAVE_LINUX_CLOSE_RANGE_H', language: 'c')
 endif
 
 if cc.has_function('strlcpy', prefix: '#define _GNU_SOURCE\n#include <string.h>')

src/shared/misc.c

@@ -24,13 +24,17 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <limits.h>
+#ifdef HAVE_LINUX_CLOSE_RANGE_H
+#  include <linux/close_range.h>
+#endif
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/file.h>
 #include <sys/time.h>
 #ifdef __linux__
+#  include <sys/syscall.h> /* for close_range */
 #  include <sys/sysinfo.h>
 #endif
 #include <sys/types.h>
@@ -511,7 +515,17 @@ static inline int close_range(int first RC_UNUSED,
 			      int last RC_UNUSED,
 			      unsigned int flags RC_UNUSED)
 {
+#ifdef SYS_close_range
+	int r = syscall(SYS_close_range, first, last, flags);
+	if (r < 0) {
+		errno = -r;
+		r = -1;
+	}
+	return r;
+#else
+	errno = ENOSYS;
 	return -1;
+#endif
 }
 #endif
 #ifndef CLOSE_RANGE_CLOEXEC