base-linux: boost max open fds to the hard rlimit

This patch increases the default limit of the maximum number of open
file descriptors to the hard limit of the system. This is needed for
complex scenarios, which require more FDs than the default of 1024
at core.

Related to issue #3581

Fixes #3721

repos/base-linux/src/core/include/core_linux_syscalls.h

@@ -19,6 +19,7 @@
 
 #define size_t __SIZE_TYPE__ /* see comment in 'linux_syscalls.h' */
 #include <sys/stat.h>
+#include <sys/resource.h>
 #include <fcntl.h>
 #undef size_t
 
@@ -72,6 +73,7 @@ inline int lx_stat(const char *path, struct stat64 *buf)
 #endif
 }
 
+
 /***********************************************************
  ** Functions used by core's io port session support code **
  ***********************************************************/
@@ -180,6 +182,27 @@ inline void lx_disable_aslr()
 }
 
 
+/***********************************
+ ** Resource-limit initialization **
+ ***********************************/
+
+inline void lx_boost_rlimit()
+{
+	rlimit rlimit { };
+
+	if (int const res = lx_syscall(SYS_getrlimit, RLIMIT_NOFILE, &rlimit)) {
+		Genode::warning("unable to obtain RLIMIT_NOFILE (", res, "), keeping limit unchanged");
+		return;
+	}
+
+	/* increase soft limit to hard limit */
+	rlimit.rlim_cur = rlimit.rlim_max;
+
+	if (int const res = lx_syscall(SYS_setrlimit, RLIMIT_NOFILE, &rlimit))
+		Genode::warning("unable to boost RLIMIT_NOFILE (", res, "), keeping limit unchanged");
+}
+
+
 /********************************************
  ** Communication over Unix-domain sockets **
  ********************************************/

repos/base-linux/src/core/platform.cc

@@ -94,6 +94,9 @@ Platform::Platform()
 	/* make 'mmap' behave deterministically */
 	lx_disable_aslr();
 
+	/* increase maximum number of open file descriptors to the hard limit */
+	lx_boost_rlimit();
+
 	/* catch control-c */
 	lx_sigaction(LX_SIGINT, sigint_handler, false);