File Operations

This document describes the file operation system calls (syscalls) in the Kyronix kernel. It is the child of Syscalls.

Syscall Table

• 0 read - Read data from a file descriptor (fd)

• 1 write - Write data to a file descriptor

• 2 open - Open a file by path

• 3 close - Close a file descriptor

• 4 stat - Get file status by path

• 5 fstat - Get file status by fd

• 6 lstat - Get file status by path (no symlink follow)

• 7 poll - Wait for events on fds

• 8 lseek - Set file offset for a fd

• 16 ioctl - Control device parameters

• 17 pread64 - Read from fd at offset

• 18 pwrite64 - Write to fd at offset

• 19 readv - Read multiple buffers from fd

• 20 writev - Write multiple buffers to fd

• 21 access - Check file accessibility by path

• 22 pipe - Create a pipe

• 23 select - Monitor multiple fds for events

• 32 dup - Duplicate a fd

• 33 dup2 - Duplicate a fd to a specific number

• 40 sendfile - Transfer data between fds

• 72 fcntl - File descriptor control operations

• 76 truncate - Truncate a file to a specified length

• 77 ftruncate - Truncate a fd to a specified length

• 78 getdents64 - Read directory entries

• 79 getcwd - Get current working directory

• 80 chdir - Change current working directory

• 81 fchdir - Change current working directory by fd

• 82 rename - Rename a file or directory

• 83 mkdir - Create a directory

• 84 rmdir - Remove a directory

• 85 creat - Create a file

• 86 link - Create a hard link

• 87 unlink - Remove a file

• 88 symlink - Create a symbolic link

• 89 readlink - Read a symbolic link

• 90 chmod - Change file permissions by path

• 91 fchmod - Change file permissions by fd

• 92 chown - Change file owner by path

• 93 fchown - Change file owner by fd

• 94 lchown - Change file owner (no symlink follow)

• 95 umask - Set file creation mask

• 137 statfs - Get filesystem statistics by path

• 138 fstatfs - Get filesystem statistics by fd

• 257 openat - Open file relative to directory fd

• 258 mkdirat - Create directory relative to directory fd

• 260 mknodat - Create device node relative to directory fd

• 261 fchownat - Change file owner relative to directory fd

• 262 newfstatat - Get file status relative to directory fd

• 263 unlinkat - Remove file relative to directory fd

• 264 renameat - Rename file relative to directory fds

• 265 linkat - Create hard link relative to directory fds

• 266 symlinkat - Create symbolic link relative to directory fd

• 267 readlinkat - Read symbolic link relative to directory fd

• 268 fchmodat - Change file permissions relative to directory fd

• 269 faccessat - Check file accessibility relative to directory fd

• 292 dup3 - Duplicate a fd with flags

• 293 pipe2 - Create a pipe with flags

• 295 preadv - Read from fd at offset with scatter-gather

• 296 pwritev - Write to fd at offset with scatter-gather

• 326 copy_file_range - Copy data between two fds

• 332 statx - Get extended file status

• 334 close_range - Close a range of fds

Path Resolution

All path-based syscalls route through path_abs() to resolve user-provided paths to absolute paths. This function applies jail root confinement via jail_root_current() and prepends the current working directory (cwd) for relative paths.

The at-relative syscalls (openat, mkdirat, unlinkat, etc.) use at_resolve() for directory fd resolution. This function validates the directory fd and combines it with the relative path.

Internal Helpers

The kernel provides user pointer validation helpers:

• uptr_ok(ptr, size) - Validates a user pointer for read access with automatic page faulting
• uptr_ok_w(ptr, size) - Validates a user pointer for write access with automatic page faulting

These helpers ensure user pointers are in valid user address space before dereferencing.

Last reviewed: 2026-07-22