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File Operations

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sys_open / sys_openat

Open a file or device. 
fd_t sys_open(addr_t path_addr, dword_t flags, mode_t_ mode)
fd_t sys_openat(fd_t at, addr_t path_addr, dword_t flags, mode_t_ mode)
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at
fd_t
(openat only) Directory file descriptor for relative paths, or AT_FDCWD for current directory.
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path_addr
addr_t
Address of null-terminated path string.
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flags
dword_t
File access mode and flags:
  • O_RDONLY (0): Read-only
  • O_WRONLY (1): Write-only
  • O_RDWR (2): Read-write
  • O_CREAT (0x40): Create if doesn’t exist
  • O_EXCL (0x80): Fail if exists (with O_CREAT)
  • O_TRUNC (0x200): Truncate to 0 length
  • O_APPEND (0x400): Append mode
  • O_NONBLOCK (0x800): Non-blocking I/O
  • O_DIRECTORY (0x10000): Fail if not directory
  • O_CLOEXEC (0x80000): Close on exec
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mode
mode_t_
Permissions for newly created file (masked by umask). Only used with O_CREAT.
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return
fd_t
Returns file descriptor number on success, negative errno on error.
Error Codes:
  • ENOENT (-2): File doesn’t exist (and O_CREAT not set)
  • EEXIST (-17): File exists (with O_CREAT | O_EXCL)
  • EACCES (-13): Permission denied
  • EISDIR (-21): Path is directory (cannot open for writing)
  • ENOTDIR (-20): Component in path is not directory
  • EMFILE (-24): Too many open files
  • ENAMETOOLONG (-36): Path too long
  • EFAULT (-14): Bad address
Source: kernel/calls.h:129-130, kernel/fs.c:67

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sys_close

Close a file descriptor. 
dword_t sys_close(fd_t fd)
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fd
fd_t
File descriptor to close.
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return
dword_t
Returns 0 on success, negative errno on error.
Error Codes:
  • EBADF (-9): Invalid file descriptor
Description: Closes the file descriptor and releases associated resources. Subsequent operations on this fd will fail with EBADF. Source: kernel/calls.h:105, 131

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sys_read

Read from a file descriptor. 
dword_t sys_read(fd_t fd_no, addr_t buf_addr, dword_t size)
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fd_no
fd_t
File descriptor to read from.
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buf_addr
addr_t
Address of buffer to store read data.
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size
dword_t
Maximum number of bytes to read.
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return
dword_t
Returns number of bytes read (may be less than size), 0 on EOF, or negative errno on error.
Error Codes:
  • EBADF (-9): Invalid file descriptor or not open for reading
  • EFAULT (-14): Invalid buffer address
  • EINTR (-4): Interrupted by signal
  • EIO (-5): I/O error
  • EISDIR (-21): fd refers to directory
Source: kernel/calls.h:77

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sys_write

Write to a file descriptor. 
dword_t sys_write(fd_t fd_no, addr_t buf_addr, dword_t size)
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fd_no
fd_t
File descriptor to write to.
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buf_addr
addr_t
Address of buffer containing data to write.
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size
dword_t
Number of bytes to write.
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return
dword_t
Returns number of bytes written (may be less than size), or negative errno on error.
Error Codes:
  • EBADF (-9): Invalid file descriptor or not open for writing
  • EFAULT (-14): Invalid buffer address
  • EFBIG (-27): File too large
  • ENOSPC (-28): No space left on device
  • EPIPE (-32): Broken pipe
Source: kernel/calls.h:79

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sys_lseek

Reposition file offset. 
dword_t sys_lseek(fd_t f, dword_t off, dword_t whence)
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f
fd_t
File descriptor.
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off
dword_t
Offset in bytes.
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whence
dword_t
Reference point:
  • SEEK_SET (0): Offset from beginning of file
  • SEEK_CUR (1): Offset from current position
  • SEEK_END (2): Offset from end of file
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return
dword_t
Returns new file offset on success, negative errno on error.
Error Codes:
  • EBADF (-9): Invalid file descriptor
  • EINVAL (-22): Invalid whence
  • ESPIPE (-29): fd is pipe or socket
Source: kernel/calls.h:85

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sys_readv / sys_writev

Read/write data into/from multiple buffers. 
dword_t sys_readv(fd_t fd_no, addr_t iovec_addr, dword_t iovec_count)
dword_t sys_writev(fd_t fd_no, addr_t iovec_addr, dword_t iovec_count)
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fd_no
fd_t
File descriptor.
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iovec_addr
addr_t
Address of array of iovec structures.
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iovec_count
dword_t
Number of iovec structures.
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return
dword_t
Returns total bytes read/written, or negative errno on error.
Description: Scatter-gather I/O operations. Each iovec structure contains a buffer address and length. Source: kernel/calls.h:78, 80

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sys_pread / sys_pwrite

Read/write at specified offset without changing file position. 
dword_t sys_pread(fd_t f, addr_t buf_addr, dword_t buf_size, off_t_ off)
dword_t sys_pwrite(fd_t f, addr_t buf_addr, dword_t size, off_t_ off)
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f
fd_t
File descriptor.
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buf_addr
addr_t
Buffer address.
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buf_size
dword_t
Number of bytes to read/write.
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off
off_t_
Offset in file.
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return
dword_t
Returns bytes read/written, or negative errno on error.
Description: Like read/write but doesn’t update the file offset. Thread-safe for concurrent operations. Source: kernel/calls.h:87-88

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File Metadata

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sys_stat / sys_fstat / sys_lstat

Get file status. 
dword_t sys_stat64(addr_t path_addr, addr_t statbuf_addr)
dword_t sys_lstat64(addr_t path_addr, addr_t statbuf_addr)
dword_t sys_fstat64(fd_t fd_no, addr_t statbuf_addr)
dword_t sys_fstatat64(fd_t at, addr_t path_addr, addr_t statbuf_addr, dword_t flags)
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path_addr
addr_t
Address of null-terminated path string.
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fd_no
fd_t
(fstat) File descriptor.
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at
fd_t
(fstatat) Directory fd for relative paths.
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statbuf_addr
addr_t
Address to store stat structure.
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flags
dword_t
(fstatat) AT_SYMLINK_NOFOLLOW to not follow symlinks.
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return
dword_t
Returns 0 on success, negative errno on error.
Description:
  • stat: Get status of file at path
  • lstat: Like stat but doesn’t follow symbolic links
  • fstat: Get status of open file descriptor
  • fstatat: stat with directory fd support
Error Codes:
  • ENOENT (-2): File doesn’t exist
  • EACCES (-13): Permission denied
  • EBADF (-9): Invalid file descriptor (fstat)
  • EFAULT (-14): Bad address
Source: kernel/calls.h:150-153

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Directory Operations

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sys_mkdir / sys_mkdirat

Create a directory. 
dword_t sys_mkdir(addr_t path_addr, mode_t_ mode)
dword_t sys_mkdirat(fd_t at_f, addr_t path_addr, mode_t_ mode)
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at_f
fd_t
(mkdirat) Directory fd for relative paths.
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path_addr
addr_t
Address of null-terminated path string.
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mode
mode_t_
Directory permissions (masked by umask).
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return
dword_t
Returns 0 on success, negative errno on error.
Error Codes:
  • EEXIST (-17): Directory already exists
  • ENOENT (-2): Parent directory doesn’t exist
  • EACCES (-13): Permission denied
  • ENOSPC (-28): No space on device
Source: kernel/calls.h:170-171

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sys_rmdir

Remove an empty directory. 
dword_t sys_rmdir(addr_t path_addr)
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path_addr
addr_t
Address of null-terminated path string.
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return
dword_t
Returns 0 on success, negative errno on error.
Error Codes:
  • ENOENT (-2): Directory doesn’t exist
  • ENOTEMPTY (-39): Directory not empty
  • ENOTDIR (-20): Path is not a directory
  • EACCES (-13): Permission denied
  • EBUSY (-16): Directory in use
Source: kernel/calls.h:136

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sys_getdents / sys_getdents64

Read directory entries. 
int_t sys_getdents(fd_t f, addr_t dirents, dword_t count)
int_t sys_getdents64(fd_t f, addr_t dirents, dword_t count)
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f
fd_t
File descriptor of open directory.
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dirents
addr_t
Buffer to store directory entries.
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count
dword_t
Size of buffer in bytes.
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return
int_t
Returns bytes read on success, 0 at end of directory, or negative errno on error.
Description: Reads directory entries into a buffer. Each entry includes inode, offset, name, and type. Source: kernel/calls.h:148-149

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File System Operations

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sys_mount

Mount a filesystem. 
dword_t sys_mount(addr_t source_addr, addr_t target_addr, addr_t type_addr, 
                  dword_t flags, addr_t data_addr)
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source_addr
addr_t
Address of device or filesystem source path.
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target_addr
addr_t
Address of mount point path.
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type_addr
addr_t
Address of filesystem type string.
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flags
dword_t
Mount flags:
  • MS_READONLY (0x1): Mount read-only
  • MS_NOSUID (0x2): Ignore suid/sgid bits
  • MS_NODEV (0x4): Disallow device files
  • MS_NOEXEC (0x8): Disallow program execution
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data_addr
addr_t
Filesystem-specific options.
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return
dword_t
Returns 0 on success, negative errno on error.
Error Codes:
  • EPERM (-1): Permission denied
  • ENOENT (-2): Mount point doesn’t exist
  • ENOTDIR (-20): Target not a directory
  • EBUSY (-16): Target in use
Source: kernel/calls.h:195

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sys_umount2

Unmount a filesystem. 
dword_t sys_umount2(addr_t target_addr, dword_t flags)
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target_addr
addr_t
Address of mount point path.
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flags
dword_t
Unmount flags (MNT_FORCE, MNT_DETACH, etc.).
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return
dword_t
Returns 0 on success, negative errno on error.
Source: kernel/calls.h:196
Create a hard link. 
dword_t sys_link(addr_t src_addr, addr_t dst_addr)
dword_t sys_linkat(fd_t src_at_f, addr_t src_addr, fd_t dst_at_f, addr_t dst_addr)
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src_addr
addr_t
Existing file path.
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dst_addr
addr_t
New link path.
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return
dword_t
Returns 0 on success, negative errno on error.
Source: kernel/calls.h:132-133
Remove a file or link. 
dword_t sys_unlink(addr_t path_addr)
dword_t sys_unlinkat(fd_t at_f, addr_t path_addr, int_t flags)
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path_addr
addr_t
Path to file to remove.
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flags
int_t
(unlinkat) AT_REMOVEDIR to remove directory.
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return
dword_t
Returns 0 on success, negative errno on error.
Source: kernel/calls.h:134-135
Create a symbolic link. 
dword_t sys_symlink(addr_t target_addr, addr_t link_addr)
dword_t sys_symlinkat(addr_t target_addr, fd_t at_f, addr_t link_addr)
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target_addr
addr_t
Target path (can be relative or absolute).
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link_addr
addr_t
Symbolic link path to create.
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return
dword_t
Returns 0 on success, negative errno on error.
Source: kernel/calls.h:140-141
Read symbolic link target. 
dword_t sys_readlink(addr_t path, addr_t buf, dword_t bufsize)
dword_t sys_readlinkat(fd_t at_f, addr_t path, addr_t buf, dword_t bufsize)
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path
addr_t
Symbolic link path.
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buf
addr_t
Buffer for target path.
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bufsize
dword_t
Buffer size.
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return
dword_t
Returns number of bytes placed in buffer, or negative errno on error.
Source: kernel/calls.h:146-147

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