zvfs: Move file operations from POSIX into ZVFS

This commit moves all operations on single files into ZVFS and makes the
POSIX subsystem call into ZVFS to perform them. It was necessary to define
a `struct zvfs_stat` to avoid a dependency cycle. Functions used
internally for file i/o operations are publicised since they won't require
any changes between various subsystems. This allows ZVFS to actually
fulfill its purpose of facilitating cooperation of different file APIs.

Signed-off-by: Jakub Klimczak <[email protected]>

Author: Jakub Klimczak

include/zephyr/sys/fdtable.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2018 Linaro Limited
+ * Copyright (c) 2025 Antmicro
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -56,10 +57,6 @@
 #define ZVFS_POLLHUP  BIT(4)
 #define ZVFS_POLLNVAL BIT(5)
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /* FIXME: use k_off_t and k_ssize_t to avoid the POSIX->Zephyr->POSIX dependency cycle */
 #ifdef CONFIG_NEWLIB_LIBC
 #ifndef _OFF_T_DECLARED
@@ -72,6 +69,12 @@ typedef _ssize_t ssize_t;
 #endif
 #endif
 
+#include <zephyr/fs/fs.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /**
  * File descriptor virtual method table.
  * Currently all operations beyond read/write/close go thru ioctl method.
@@ -236,6 +239,15 @@ static inline int zvfs_fdtable_call_ioctl(const struct fd_op_vtable *vtable, voi
 	return res;
 }
 
+/**
+ * Structure for result of the ZFD_IOCTL_STAT ioctl call.
+ * Contains fields for all currently supported details. Defined to avoid POSIX dependency.
+ */
+struct zvfs_stat {
+	off_t size;
+	uint32_t mode;
+};
+
 struct zvfs_pollfd {
 	int fd;
 	short events;
@@ -286,6 +298,88 @@ enum {
 	ZFD_IOCTL_FIONBIO = 0x5421,
 };
 
+/**
+ * @brief Open a file with a given name.
+ *
+ * @param name Name of the file
+ * @param flags Access modes for @ref fs_open
+ * @param vtable Pointer to structure with appropriate i/o functions
+ *
+ * @return Index of newly created file descriptor on success, -1 on error with errno set.
+ */
+int zvfs_open(const char *name, int flags, struct fd_op_vtable *vtable);
+
+/**
+ * @brief Get information about file.
+ *
+ * @param fd File descriptor index
+ * @param buf Pointer to result structure
+ *
+ * @return 0 on success, -1 with errno set on error.
+ */
+int zvfs_fstat(int fd, struct zvfs_stat *buf);
+
+/**
+ * @brief Close file.
+ *
+ * @param fd File descriptor index
+ *
+ * @return 0 on success, -1 with errno set on error.
+ */
+int zvfs_close(int fd);
+
+/**
+ * @brief Read bytes from file.
+ *
+ * @param fd File descriptor index
+ * @param buf Destination buffer
+ * @param sz Number of bytes to read
+ * @param from_offset Pointer to variable specifying starting position;
+ * current offset will be used if NULL
+ *
+ * @return Number of bytes read successfully, or -1 with errno set on failure
+ */
+ssize_t zvfs_read(int fd, void *buf, size_t sz, const size_t *from_offset);
+
+/**
+ * @brief Write bytes to file.
+ *
+ * @param fd File descriptor index
+ * @param buf Source buffer
+ * @param sz Number of bytes to write
+ * @param from_offset Pointer to variable specifying starting position;
+ * current offset will be used if NULL
+ *
+ * @return Number of bytes written successfully, or -1 with errno set on failure
+ */
+ssize_t zvfs_write(int fd, const void *buf, size_t sz, const size_t *from_offset);
+
+#ifdef CONFIG_ZVFS_DEFAULT_FILE_VMETHODS
+int zvfs_ioctl_vmeth(void *obj, unsigned int request, va_list args);
+int zvfs_close_vmeth(void *obj);
+ssize_t zvfs_write_vmeth(void *obj, const void *buffer, size_t count);
+ssize_t zvfs_read_vmeth(void *obj, void *buffer, size_t count);
+#endif
+
+/**
+ * @brief Delete file or directory.
+ *
+ * @param path Path or name of file to be removed.
+ *
+ * @return 0 on success, -1 with errno set on error.
+ */
+int zvfs_unlink(const char *path);
+
+/**
+ * @brief Rename file or directory, moving it if necessary.
+ *
+ * @param old Current name
+ * @param newp Target name
+ *
+ * @return 0 on success, -1 with errno set on error.
+ */
+int zvfs_rename(const char *old, const char *newp);
+
 #ifdef __cplusplus
 }
 #endif

lib/os/Kconfig

@@ -10,6 +10,17 @@ config FDTABLE
 	  for any I/O object implementing POSIX I/O semantics (i.e. read/write +
 	  aux operations).
 
+if FDTABLE
+
+config ZVFS_DEFAULT_FILE_VMETHODS
+	bool "ZVFS default virtual methods for files"
+	default y
+	help
+	  Provide typical file operations, which can be referenced in a struct fd_op_vtable
+	  and subsequently called by ZVFS functions.
+
+endif
+
 config ZVFS_OPEN_MAX
 	int "Maximum number of open file descriptors"
 	default 0

lib/os/fdtable.c

@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2018 Linaro Limited
  * Copyright (c) 2024 Tenstorrent AI ULC
+ * Copyright (c) 2025 Antmicro
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -23,8 +24,9 @@
 #include <zephyr/sys/speculation.h>
 #include <zephyr/internal/syscall_handler.h>
 #include <zephyr/sys/atomic.h>
+#include <zephyr/fs/fs.h>
 
-struct stat;
+K_MEM_SLAB_DEFINE(file_desc_slab, sizeof(struct fs_file_t), ZVFS_OPEN_SIZE, 4);
 
 struct fd_entry {
 	void *obj;
@@ -73,6 +75,46 @@ static struct fd_entry fdtable[ZVFS_OPEN_SIZE] = {
 #endif
 };
 
+int zvfs_open(const char *name, int flags, struct fd_op_vtable *vtable)
+{
+	int rc, fd;
+	struct fs_file_t *ptr = NULL;
+
+	fd = zvfs_reserve_fd();
+	if (fd < 0) {
+		return -1;
+	}
+
+	rc = k_mem_slab_alloc(&file_desc_slab, (void **)&ptr, K_NO_WAIT);
+	if (rc < 0) {
+		rc = -EMFILE;
+		goto out_err;
+	}
+
+	fs_file_t_init(ptr);
+
+	rc = fs_open(ptr, name, flags);
+	if (rc < 0) {
+		goto out_err;
+	}
+
+	zvfs_finalize_fd(fd, ptr, vtable);
+
+	goto out;
+
+out_err:
+	if (ptr != NULL) {
+		k_mem_slab_free(&file_desc_slab, ptr);
+	}
+
+	zvfs_free_fd(fd);
+	errno = -rc;
+	return -1;
+
+out:
+	return fd;
+}
+
 static K_MUTEX_DEFINE(fdtable_lock);
 
 static int z_fd_ref(int fd)
@@ -432,7 +474,7 @@ int zvfs_fileno(FILE *file)
 	return (struct fd_entry *)file - fdtable;
 }
 
-int zvfs_fstat(int fd, struct stat *buf)
+int zvfs_fstat(int fd, struct zvfs_stat *buf)
 {
 	if (_check_fd(fd) < 0) {
 		return -1;
@@ -535,6 +577,27 @@ int zvfs_ioctl(int fd, unsigned long request, va_list args)
 	return fdtable[fd].vtable->ioctl(fdtable[fd].obj, request, args);
 }
 
+int zvfs_unlink(const char *path)
+{
+	int res = fs_unlink(path);
+
+	if (res < 0) {
+		errno = -res;
+		return -1;
+	}
+	return 0;
+}
+
+int zvfs_rename(const char *old, const char *newp)
+{
+	int res = fs_rename(old, newp);
+
+	if (res < 0) {
+		errno = -res;
+		return -1;
+	}
+	return 0;
+}
 
 #if defined(CONFIG_POSIX_DEVICE_IO)
 /*

lib/os/zvfs/CMakeLists.txt

@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: Apache-2.0
 
 zephyr_library()
+zephyr_library_sources_ifdef(CONFIG_ZVFS_DEFAULT_FILE_VMETHODS zvfs_file_vmethods.c)
 zephyr_library_sources_ifdef(CONFIG_ZVFS_EVENTFD zvfs_eventfd.c)
 zephyr_library_sources_ifdef(CONFIG_ZVFS_POLL zvfs_poll.c)
 zephyr_library_sources_ifdef(CONFIG_ZVFS_SELECT zvfs_select.c)