posix: deprecate POSIX_MAX_FDS and add POSIX_DEVICE_IO

The POSIX_MAX_FDS option does not correspond to any standard
POSIX option. It was used to define the size of the file
descriptor table, which is by no means exclusively used by
POSIX (also net, fs, ...).

POSIX_MAX_FDS is being deprecated in order to ensure that
Zephyr's POSIX Kconfig variables correspond to those defined in
the specification, as of IEEE 1003.1-2017. Namely,
POSIX_OPEN_MAX. CONFIG_POSIX_MAX_OPEN_FILES is being deprecated
for the same reason.

To mitigate any possible layering violations, that option is
not user selectable. It tracks the newly added
CONFIG_ZVFS_OPEN_MAX option, which is native to Zephyr.

With this deprecation, we introduce the following Kconfig
options that map directly to standard POSIX Option Groups by
simply removing "CONFIG_":

* CONFIG_POSIX_DEVICE_IO

Similarly, with this deprecation, we introduce the following
Kconfig options that map directly to standard POSIX Options by
simply removing "CONFIG":

* CONFIG_POSIX_OPEN_MAX

In order to maintain parity with the current feature set, we
introduce the following Kconfig options.

* CONFIG_POSIX_DEVICE_IO_ALIAS_CLOSE
* CONFIG_POSIX_DEVICE_IO_ALIAS_OPEN
* CONFIG_POSIX_DEVICE_IO_ALIAS_READ
* CONFIG_POSIX_DEVICE_IO_ALIAS_WRITE

Gate open(), close(), read(), and write() via the
CONFIG_POSIX_DEVICE_IO Kconfig option and move
implementations into device_io.c, to be conformant with the
spec.

Lastly, stage function names for upcoming ZVFS work, to be
completed as part of the LTSv3 Roadmap (e.g. zvfs_open(), ..).

Signed-off-by: Chris Friedt <[email protected]>

doc/connectivity/networking/net_config_guide.rst

@@ -87,7 +87,7 @@ Socket Options
   Maximum number of supported poll() entries. One needs to select proper value here depending
   on how many BSD sockets are polled in the system.
 
-:kconfig:option:`CONFIG_POSIX_MAX_FDS`
+:kconfig:option:`CONFIG_ZVFS_OPEN_MAX`
   Maximum number of open file descriptors, this includes files, sockets, special devices, etc.
   One needs to select proper value here depending on how many BSD sockets are created in
   the system.

doc/services/portability/posix/kconfig/index.rst

@@ -26,8 +26,8 @@ implementation of the POSIX API.
 * :kconfig:option:`CONFIG_NET_SOCKETS_POLL_MAX`
 * :kconfig:option:`CONFIG_POSIX_API`
 * :kconfig:option:`CONFIG_POSIX_FS`
-* :kconfig:option:`CONFIG_POSIX_MAX_FDS`
-* :kconfig:option:`CONFIG_POSIX_MAX_OPEN_FILES`
+* :kconfig:option:`CONFIG_ZVFS_OPEN_MAX`
+* :kconfig:option:`CONFIG_POSIX_OPEN_MAX`
 * :kconfig:option:`CONFIG_POSIX_MQUEUE`
 * :kconfig:option:`CONFIG_POSIX_RTSIG_MAX`
 * :kconfig:option:`CONFIG_POSIX_SIGNAL`

drivers/modem/Kconfig

@@ -155,7 +155,7 @@ config MODEM_SOCKET
 	  modem_socket_init().
 	  Note that the modem socket uses runtime allocated file descriptors
 	  reserved from the fdtable, for which the max count is set using the
-	  Kconfig option POSIX_MAX_FDS. Make sure to update this value as both
+	  Kconfig option ZVFS_OPEN_MAX. Make sure to update this value as both
 	  the modem sockets and the POSIX_API, if used, share them.
 
 config MODEM_SOCKET_PACKET_COUNT

include/zephyr/net/socket_select.h

@@ -29,7 +29,7 @@ extern "C" {
 /** @cond INTERNAL_HIDDEN */
 
 typedef struct zsock_fd_set {
-	uint32_t bitset[(CONFIG_POSIX_MAX_FDS + 31) / 32];
+	uint32_t bitset[(CONFIG_ZVFS_OPEN_MAX + 31) / 32];
 } zsock_fd_set;
 
 /** @endcond */

include/zephyr/posix/posix_features.h

@@ -209,7 +209,7 @@
 #define _POSIX_MQ_PRIO_MAX                  (32)
 #define _POSIX_NAME_MAX                     (14)
 #define _POSIX_NGROUPS_MAX                  (8)
-#define _POSIX_OPEN_MAX                     CONFIG_POSIX_MAX_FDS
+#define _POSIX_OPEN_MAX                     CONFIG_POSIX_OPEN_MAX
 #define _POSIX_PATH_MAX                     (256)
 #define _POSIX_PIPE_BUF                     (512)
 #define _POSIX_RE_DUP_MAX                   (255)

include/zephyr/posix/sys/sysconf.h

@@ -268,7 +268,7 @@ enum {
 #define __z_posix_sysconf_SC_NGROUPS_MAX                  _POSIX_NGROUPS_MAX
 #define __z_posix_sysconf_SC_MQ_OPEN_MAX                  MQ_OPEN_MAX
 #define __z_posix_sysconf_SC_MQ_PRIO_MAX                  MQ_PRIO_MAX
-#define __z_posix_sysconf_SC_OPEN_MAX                     CONFIG_POSIX_MAX_FDS
+#define __z_posix_sysconf_SC_OPEN_MAX                     CONFIG_ZVFS_OPEN_MAX
 #define __z_posix_sysconf_SC_PAGE_SIZE                    PAGE_SIZE
 #define __z_posix_sysconf_SC_PAGESIZE                     PAGESIZE
 #define __z_posix_sysconf_SC_THREAD_DESTRUCTOR_ITERATIONS PTHREAD_DESTRUCTOR_ITERATIONS

lib/libc/Kconfig

@@ -102,6 +102,10 @@ config NEWLIB_LIBC
 	depends on !NATIVE_APPLICATION
 	depends on NEWLIB_LIBC_SUPPORTED
 	select NEED_LIBC_MEM_PARTITION
+	imply POSIX_DEVICE_IO_ALIAS_CLOSE
+	imply POSIX_DEVICE_IO_ALIAS_OPEN
+	imply POSIX_DEVICE_IO_ALIAS_READ
+	imply POSIX_DEVICE_IO_ALIAS_WRITE
 	imply POSIX_FD_MGMT_ALIAS_LSEEK
 	help
 	  Build with newlib library. The newlib library is expected to be

lib/os/Kconfig

@@ -10,6 +10,15 @@ config FDTABLE
 	  for any I/O object implementing POSIX I/O semantics (i.e. read/write +
 	  aux operations).
 
+config ZVFS_OPEN_MAX
+	int "Maximum number of open file descriptors"
+	default 16 if WIFI_NM_WPA_SUPPLICANT
+	default 16 if POSIX_API
+	default 4
+	help
+	  Maximum number of open file descriptors, this includes
+	  files, sockets, special devices, etc.
+
 config PRINTK_SYNC
 	bool "Serialize printk() calls"
 	default y if SMP && MP_MAX_NUM_CPUS > 1 && !(EFI_CONSOLE && LOG)

lib/os/fdtable.c

@@ -31,12 +31,14 @@ struct fd_entry {
 	struct k_condvar cond;
 };
 
-#ifdef CONFIG_POSIX_API
+#if defined(CONFIG_POSIX_DEVICE_IO)
 static const struct fd_op_vtable stdinout_fd_op_vtable;
-#endif
 
-static struct fd_entry fdtable[CONFIG_POSIX_MAX_FDS] = {
-#ifdef CONFIG_POSIX_API
+BUILD_ASSERT(CONFIG_ZVFS_OPEN_MAX >= 3, "CONFIG_ZVFS_OPEN_MAX >= 3 for CONFIG_POSIX_DEVICE_IO");
+#endif /* defined(CONFIG_POSIX_DEVICE_IO) */
+
+static struct fd_entry fdtable[CONFIG_ZVFS_OPEN_MAX] = {
+#if defined(CONFIG_POSIX_DEVICE_IO)
 	/*
 	 * Predefine entries for stdin/stdout/stderr.
 	 */
@@ -62,9 +64,7 @@ static struct fd_entry fdtable[CONFIG_POSIX_MAX_FDS] = {
 		.cond = Z_CONDVAR_INITIALIZER(fdtable[2].cond),
 	},
 #else
-	{
-	0
-	},
+	{0},
 #endif
 };
 
@@ -296,9 +296,7 @@ int z_alloc_fd(void *obj, const struct fd_op_vtable *vtable)
 	return fd;
 }
 
-#ifdef CONFIG_POSIX_API
-
-ssize_t read(int fd, void *buf, size_t sz)
+ssize_t zvfs_read(int fd, void *buf, size_t sz)
 {
 	ssize_t res;
 
@@ -314,9 +312,8 @@ ssize_t read(int fd, void *buf, size_t sz)
 
 	return res;
 }
-FUNC_ALIAS(read, _read, ssize_t);
 
-ssize_t write(int fd, const void *buf, size_t sz)
+ssize_t zvfs_write(int fd, const void *buf, size_t sz)
 {
 	ssize_t res;
 
@@ -332,9 +329,8 @@ ssize_t write(int fd, const void *buf, size_t sz)
 
 	return res;
 }
-FUNC_ALIAS(write, _write, ssize_t);
 
-int close(int fd)
+int zvfs_close(int fd)
 {
 	int res;
 
@@ -352,7 +348,6 @@ int close(int fd)
 
 	return res;
 }
-FUNC_ALIAS(close, _close, int);
 
 #ifdef CONFIG_POSIX_FSYNC
 int fsync(int fd)
@@ -372,8 +367,8 @@ off_t zvfs_lseek(int fd, off_t offset, int whence)
 		return -1;
 	}
 
-	return z_fdtable_call_ioctl(fdtable[fd].vtable, fdtable[fd].obj, ZFD_IOCTL_LSEEK,
-			  offset, whence);
+	return z_fdtable_call_ioctl(fdtable[fd].vtable, fdtable[fd].obj, ZFD_IOCTL_LSEEK, offset,
+				    whence);
 }
 
 int ioctl(int fd, unsigned long request, ...)
@@ -406,6 +401,7 @@ int zvfs_fcntl(int fd, int cmd, va_list args)
 	return res;
 }
 
+#if defined(CONFIG_POSIX_DEVICE_IO)
 /*
  * fd operations for stdio/stdout/stderr
  */
@@ -420,7 +416,7 @@ static ssize_t stdinout_read_vmeth(void *obj, void *buffer, size_t count)
 static ssize_t stdinout_write_vmeth(void *obj, const void *buffer, size_t count)
 {
 #if defined(CONFIG_BOARD_NATIVE_POSIX)
-	return write(1, buffer, count);
+	return zvfs_write(1, buffer, count);
 #elif defined(CONFIG_NEWLIB_LIBC) || defined(CONFIG_ARCMWDT_LIBC)
 	return z_impl_zephyr_write_stdout(buffer, count);
 #else
@@ -441,4 +437,4 @@ static const struct fd_op_vtable stdinout_fd_op_vtable = {
 	.ioctl = stdinout_ioctl_vmeth,
 };
 
-#endif /* CONFIG_POSIX_API */
+#endif /* defined(CONFIG_POSIX_DEVICE_IO) */

lib/posix/options/CMakeLists.txt

@@ -37,9 +37,13 @@ add_subdirectory_ifdef(CONFIG_GETOPT getopt)
 zephyr_library_sources_ifdef(CONFIG_EVENTFD eventfd.c)
 zephyr_library_sources_ifdef(CONFIG_FNMATCH fnmatch.c)
 zephyr_library_sources_ifdef(CONFIG_GETENTROPY getentropy.c)
-zephyr_library_sources_ifdef(CONFIG_POSIX_API perror.c)
 zephyr_library_sources_ifdef(CONFIG_POSIX_ASYNCHRONOUS_IO aio.c)
 zephyr_library_sources_ifdef(CONFIG_POSIX_CONFSTR confstr.c)
+zephyr_library_sources_ifdef(CONFIG_POSIX_DEVICE_IO
+  # perror should be moved to the common libc
+  perror.c
+  device_io.c
+)
 zephyr_library_sources_ifdef(CONFIG_POSIX_ENV env.c)
 zephyr_library_sources_ifdef(CONFIG_POSIX_FD_MGMT
   fd_mgmt.c

lib/posix/options/Kconfig

@@ -13,6 +13,16 @@ config POSIX_API
 	  Enable mostly-standards-compliant implementations of
 	  various POSIX (IEEE 1003.1) APIs.
 
+config POSIX_OPEN_MAX
+	int
+	default ZVFS_OPEN_MAX
+	help
+	  The maximum number of files that a process can have open at one time. This option is not
+	  directly user-configurable but can be adjusted via CONFIG_ZVFS_OPEN_MAX.
+
+	  For more information, please see
+	  https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/limits.h.html
+
 config PTHREAD_IPC
 	bool "POSIX pthread IPC API"
 	default y if POSIX_API
@@ -26,9 +36,9 @@ rsource "Kconfig.aio"
 rsource "Kconfig.barrier"
 rsource "Kconfig.cond"
 rsource "Kconfig.confstr"
+rsource "Kconfig.device_io"
 rsource "Kconfig.env"
 rsource "Kconfig.eventfd"
-rsource "Kconfig.fdtable"
 rsource "Kconfig.fd_mgmt"
 rsource "Kconfig.fnmatch"
 rsource "Kconfig.fs"

lib/posix/options/Kconfig.deprecated

@@ -28,6 +28,26 @@ config POSIX_LIMITS_RTSIG_MAX
 
 	  Please use CONFIG_POSIX_RTSIG_MAX instead.
 
+config POSIX_MAX_FDS
+	int "Maximum number of open file descriptors [DEPRECATED]"
+	default 0
+	help
+	  This option is deprecated.
+
+	  Please use CONFIG_POSIX_OPEN_MAX instead.
+
+	  See also CONFIG_ZVFS_OPEN_MAX.
+
+config POSIX_MAX_OPEN_FILES
+	int "Maximum number of open file descriptors [DEPRECATED]"
+	default 0
+	help
+	  This option is deprecated.
+
+	  Please use CONFIG_POSIX_OPEN_MAX instead.
+
+	  See also CONFIG_ZVFS_OPEN_MAX.
+
 config TIMER
 	bool "Timer support [DEPRECATED]"
 	select DEPRECATED

lib/posix/options/Kconfig.device_io

@@ -0,0 +1,42 @@
+# Copyright (c) 2024 Tenstorrent AI ULC
+#
+# SPDX-License-Identifier: Apache-2.0
+
+menuconfig POSIX_DEVICE_IO
+	bool "POSIX Device IO"
+	default y if POSIX_API
+	select FDTABLE
+	help
+	  Select 'y' here and Zephyr will provide an implementation of the POSIX_DEVICE_IO Option
+	  Group such as FD_CLR(), FD_ISSET(), FD_SET(), FD_ZERO(), close(), fdopen(), fileno(), open(),
+	  poll(), pread(), pselect(), pwrite(), read(), select(), and write().
+
+	  For more informnation, please see
+	  https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_subprofiles.html
+
+if POSIX_DEVICE_IO
+
+# These options are intended to be used for compatibility with external POSIX
+# implementations such as those in Newlib or Picolibc.
+
+config POSIX_DEVICE_IO_ALIAS_CLOSE
+	bool
+	help
+	  Select 'y' here and Zephyr will provide an alias for close() as _close().
+
+config POSIX_DEVICE_IO_ALIAS_OPEN
+	bool
+	help
+	  Select 'y' here and Zephyr will provide an alias for open() as _open().
+
+config POSIX_DEVICE_IO_ALIAS_READ
+	bool
+	help
+	  Select 'y' here and Zephyr will provide an alias for read() as _read().
+
+config POSIX_DEVICE_IO_ALIAS_WRITE
+	bool
+	help
+	  Select 'y' here and Zephyr will provide an alias for write() as _write().
+
+endif # POSIX_DEVICE_IO

lib/posix/options/Kconfig.fs

@@ -12,13 +12,6 @@ menuconfig POSIX_FS
 
 if POSIX_FS
 
-config POSIX_MAX_OPEN_FILES
-	int "Maximum number of open file descriptors"
-	default 16
-	help
-	  Maximum number of open files. Note that this setting
-	  is additionally bounded by CONFIG_POSIX_MAX_FDS.
-
 config POSIX_FSYNC
 	bool "Support for fsync()"
 	default y

lib/posix/options/device_io.c

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2024, Tenstorrent AI ULC
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include <zephyr/posix/poll.h>
+#include <zephyr/posix/unistd.h>
+#include <zephyr/posix/sys/select.h>
+#include <zephyr/posix/sys/socket.h>
+
+/* prototypes for external, not-yet-public, functions in fdtable.c or fs.c */
+int zvfs_close(int fd);
+int zvfs_open(const char *name, int flags);
+ssize_t zvfs_read(int fd, void *buf, size_t sz);
+ssize_t zvfs_write(int fd, const void *buf, size_t sz);
+
+int close(int fd)
+{
+	return zvfs_close(fd);
+}
+#ifdef CONFIG_POSIX_DEVICE_IO_ALIAS_CLOSE
+FUNC_ALIAS(close, _close, int);
+#endif /* CONFIG_POSIX_DEVICEIO_ALIAS_CLOSE */
+
+int open(const char *name, int flags, ...)
+{
+	/* FIXME: necessarily need to check for O_CREAT and unpack ... if set */
+	return zvfs_open(name, flags);
+}
+#ifdef CONFIG_POSIX_DEVICE_IO_ALIAS_OPEN
+FUNC_ALIAS(open, _open, int);
+#endif /* CONFIG_POSIX_DEVICEIO_ALIAS_OPEN */
+
+int poll(struct pollfd *fds, int nfds, int timeout)
+{
+	/* TODO: create  zvfs_poll() and dispatch to subsystems based on file type */
+	return zsock_poll(fds, nfds, timeout);
+}
+
+ssize_t read(int fd, void *buf, size_t sz)
+{
+	return zvfs_read(fd, buf, sz);
+}
+#ifdef CONFIG_POSIX_DEVICE_IO_ALIAS_READ
+FUNC_ALIAS(read, _read, ssize_t);
+#endif /* CONFIG_POSIX_DEVICEIO_ALIAS_READ */
+
+int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout)
+{
+	/* TODO: create  zvfs_select() and dispatch to subsystems based on file type */
+	return zsock_select(nfds, readfds, writefds, exceptfds, (struct zsock_timeval *)timeout);
+}
+
+ssize_t write(int fd, const void *buf, size_t sz)
+{
+	return zvfs_write(fd, buf, sz);
+}
+#ifdef CONFIG_POSIX_DEVICE_IO_ALIAS_WRITE
+FUNC_ALIAS(write, _write, ssize_t);
+#endif /* CONFIG_POSIX_DEVICEIO_ALIAS_WRITE */