lib: Introduce a way to set minimum file descriptors count

Instead of user trying to figure out what is the amount of file /
socket descriptors in the system, let the various subsystems etc.
specify their need using a Kconfig option. The build system will
then add these smaller values together and set a suitable file
descriptor count in the system.

This works the same way as the heap size calculation introduced
in commit 3fbf124

Signed-off-by: Jukka Rissanen <[email protected]>

Author: jukkar

include/zephyr/sys/fdtable.h

@@ -245,7 +245,7 @@ struct zvfs_pollfd {
 __syscall int zvfs_poll(struct zvfs_pollfd *fds, int nfds, int poll_timeout);
 
 struct zvfs_fd_set {
-	uint32_t bitset[(CONFIG_ZVFS_OPEN_MAX + 31) / 32];
+	uint32_t bitset[(ZVFS_OPEN_SIZE + 31) / 32];
 };
 
 /** @brief Number of file descriptors which can be added @ref zvfs_fd_set */

lib/os/CMakeLists.txt

@@ -13,6 +13,36 @@ zephyr_sources(
   thread_entry.c
   )
 
+if(CONFIG_ZVFS_OPEN_IGNORE_MIN)
+  set(final_fd_size ${CONFIG_ZVFS_OPEN_MAX})
+else()
+  # Import all custom ZVFS_OPEN_ size requirements
+  import_kconfig(CONFIG_ZVFS_OPEN_ADD_SIZE_ ${DOTCONFIG} add_size_keys)
+
+  # Calculate the sum of all "ADD_SIZE" requirements
+  set(add_size_sum 0)
+  foreach(add_size ${add_size_keys})
+    math(EXPR add_size_sum "${add_size_sum} + ${${add_size}}")
+  endforeach()
+
+  if(CONFIG_ZVFS_OPEN_MAX LESS "${add_size_sum}")
+    # Only warn if default value 0 has been modified
+    if(NOT CONFIG_ZVFS_OPEN_MAX EQUAL 0)
+      message(WARNING "
+        CONFIG_ZVFS_OPEN_MAX is less than requested minimum:
+          ${CONFIG_ZVFS_OPEN_MAX} < ${add_size_sum}
+        Setting the file descriptor size to ${add_size_sum}")
+    endif()
+
+    set(final_fd_size ${add_size_sum})
+  else()
+    # CONFIG_ZVFS_OPEN_MAX was greater than the sum of the requirements
+    set(final_fd_size ${CONFIG_ZVFS_OPEN_MAX})
+  endif()
+endif()
+
+zephyr_compile_definitions(ZVFS_OPEN_SIZE=${final_fd_size})
+
 zephyr_sources_ifdef(CONFIG_FDTABLE fdtable.c)
 zephyr_syscall_header_ifdef(CONFIG_FDTABLE
   ${ZEPHYR_BASE}/include/zephyr/sys/fdtable.h

lib/os/Kconfig

@@ -12,13 +12,27 @@ config FDTABLE
 
 config ZVFS_OPEN_MAX
 	int "Maximum number of open file descriptors"
-	default 24 if NRF70_ENABLE_DUAL_VIF
-	default 16 if WIFI_NM_WPA_SUPPLICANT
-	default 16 if POSIX_API
-	default 4
+	default 0
 	help
 	  Maximum number of open file descriptors, this includes
-	  files, sockets, special devices, etc.
+	  files, sockets, special devices, etc. If subsystems
+	  specify ZVFS_OPEN_ADD_SIZE_* options, these will be added together
+	  and the sum will be compared to the ZVFS_OPEN_MAX value.
+	  If the sum is greater than the ZVFS_OPEN_MAX option (even if this
+	  has the default 0 value), then the actual heap size will be rounded up
+	  to the sum of the individual requirements (unless the
+	  ZVFS_OPEN_IGNORE_MIN option is enabled). If the final value, after
+	  considering both this option as well as sum of the custom
+	  requirements, ends up being zero, then no file descriptors will be
+	  available.
+
+config ZVFS_OPEN_IGNORE_MIN
+	bool "Ignore the minimum fd size requirement"
+	help
+	  This option can be set to force setting a smaller file descriptor
+	  size than what's specified by enabled subsystems. This can be useful
+	  when optimizing memory usage and a more precise minimum fd size
+	  is known for a given application.
 
 config PRINTK_SYNC
 	bool "Serialize printk() calls"

lib/os/fdtable.c

@@ -39,10 +39,10 @@ struct fd_entry {
 #if defined(CONFIG_POSIX_DEVICE_IO)
 static const struct fd_op_vtable stdinout_fd_op_vtable;
 
-BUILD_ASSERT(CONFIG_ZVFS_OPEN_MAX >= 3, "CONFIG_ZVFS_OPEN_MAX >= 3 for CONFIG_POSIX_DEVICE_IO");
+BUILD_ASSERT(ZVFS_OPEN_SIZE >= 3, "ZVFS_OPEN_SIZE >= 3 for CONFIG_POSIX_DEVICE_IO");
 #endif /* defined(CONFIG_POSIX_DEVICE_IO) */
 
-static struct fd_entry fdtable[CONFIG_ZVFS_OPEN_MAX] = {
+static struct fd_entry fdtable[ZVFS_OPEN_SIZE] = {
 #if defined(CONFIG_POSIX_DEVICE_IO)
 	/*
 	 * Predefine entries for stdin/stdout/stderr.

modules/hostap/Kconfig

@@ -24,6 +24,10 @@ config WIFI_NM_WPA_SUPPLICANT
 
 if WIFI_NM_WPA_SUPPLICANT
 
+config ZVFS_OPEN_ADD_SIZE_WIFI_NM_WPA_SUPPLICANT
+	int "Number of socket descriptors needed by hostap"
+	default 12
+
 config WIFI_NM_WPA_SUPPLICANT_GLOBAL_HEAP
 	bool "Use Zephyr kernel heap for Wi-Fi driver"
 	default y

modules/nrf_wifi/Kconfig

@@ -4,4 +4,8 @@
 config ZEPHYR_NRF_WIFI_MODULE
 	bool
 
+config ZVFS_OPEN_ADD_SIZE_NRF70_ENABLE_DUAL_VIF
+	int "Number of socket descriptors needed by nrf wifi driver"
+	default 8
+
 source "modules/nrf_wifi/bus/Kconfig"

subsys/net/lib/dns/dispatcher.c

@@ -31,7 +31,7 @@ NET_BUF_POOL_DEFINE(dns_msg_pool, DNS_RESOLVER_BUF_CTR,
 
 static struct socket_dispatch_table {
 	struct dns_socket_dispatcher *ctx;
-} dispatch_table[CONFIG_ZVFS_OPEN_MAX];
+} dispatch_table[ZVFS_OPEN_SIZE];
 
 static int dns_dispatch(struct dns_socket_dispatcher *dispatcher,
 			int sock, struct sockaddr *addr, size_t addrlen,

subsys/net/lib/sockets/socket_obj_core.c

@@ -20,8 +20,8 @@ static K_MUTEX_DEFINE(sock_obj_mutex);
 /* Allocate some extra socket objects so that we can track
  * closed sockets and get some historical statistics.
  */
-static struct sock_obj sock_objects[CONFIG_ZVFS_OPEN_MAX * 2] = {
-	[0 ... ((CONFIG_ZVFS_OPEN_MAX * 2) - 1)] = {
+static struct sock_obj sock_objects[ZVFS_OPEN_SIZE * 2] = {
+	[0 ... ((ZVFS_OPEN_SIZE * 2) - 1)] = {
 		.fd = -1,
 		.init_done = false,
 	}