Module posix.fcntl

File Control.

Low-level control over file descriptors, including creating new file descriptors with open.

Functions

fcntl (fd, cmd[, arg=0]) Manipulate file descriptor.
open (path, oflags[, mode=511]) Open a file.
posix_fadvise (fd, offset, len, advice) Instruct kernel on appropriate cache behaviour for a file or file segment.

Constants

posix.fcntl Fcntl constants.

Tables

flock Advisory file locks.


Functions

fcntl (fd, cmd[, arg=0])
Manipulate file descriptor.

Parameters:

  • fd int file descriptor to act on
  • cmd int operation to perform
  • arg int or flock when cmd is F_GETLK, F_SETLK or F_SETLKW, then arg is a flock table, otherwise an integer with meaning dependent upon the value of cmd. (default 0)

Returns:

    integer return value depending on cmd, if successful

Or

  1. nil
  2. string error message
  3. int errnum

See also:

Usage:

    local flag = P.fcntl (fd, P.F_GETFL)
open (path, oflags[, mode=511])
Open a file.

Parameters:

  • path string
  • oflags int bitwise OR of zero or more of O_RDONLY, O_WRONLY, O_RDWR, O_APPEND, O_CREAT, O_DSYNC, O_EXCL, O_NOCTTY, O_NONBLOCK, O_RSYNC, O_SYNC, O_TRUNC
  • mode int access modes used by O_CREAT (default 511)

Returns:

    int file descriptor for path, if successful

Or

  1. nil
  2. string error message
  3. int errnum

See also:

Usage:

    fd = P.open ("data", bit.bor (P.O_CREAT, P.O_RDWR), bit.bor (P.S_IRWXU, P.S_IRGRP))
posix_fadvise (fd, offset, len, advice)
Instruct kernel on appropriate cache behaviour for a file or file segment.

Parameters:

  • fd int open file descriptor
  • offset int start of region
  • len int number of bytes in region
  • advice int one of POSIX_FADV_NORMAL, POSIX_FADV_SEQUENTIAL, POSIX_FADV_RANDOM, POSIX_FADV_NOREUSE, POSIX_FADV_WILLNEED or POSIX_FADV_DONTNEED

Returns:

    int 0, if successful

Or

  1. nil
  2. string error message
  3. int errnum

See also:

Constants

posix.fcntl
Fcntl constants. Any constants not available in the underlying system will be nil valued.

Fields:

  • F_DUPFD int duplicate file descriptor
  • F_GETFD int get file descriptor flags
  • F_SETFD int set file descriptor flags
  • F_GETFL int get file status flags
  • F_SETFL int set file status flags
  • F_GETLK int get record locking information
  • F_SETLK int set record locking information
  • F_SETLKW int set lock, and wait if blocked
  • F_GETOWN int get SIGIO/SIGURG process owner
  • F_SETOWN int set SIGIO/SIGURG process owner
  • F_RDLCK int shared or read lock
  • F_WRLCK int exclusive or write lock
  • F_UNLCK int unlock
  • O_RDONLY int open for reading only
  • O_WRONLY int open for writing only
  • O_RDWR int open for reading and writing
  • O_APPEND int set append mode
  • O_CREAT int create if nonexistent
  • O_DSYNC int synchronise io data integrity
  • O_EXCL int error if file already exists
  • O_NOCTTY int don't assign controlling terminal
  • O_NONBLOCK int no delay
  • O_RSYNC int synchronise file read integrity
  • O_SYNC int synchronise file write integrity
  • O_TRUNC int truncate to zero length
  • POSIX_FADV_NORMAL int no advice
  • POSIX_FADV_SEQUENTIAL int expecting to access data sequentially
  • POSIX_FADV_RANDOM int expecting to access data randomly
  • POSIX_FADV_NOREUSE int expecting to access data once only
  • POSIX_FADV_WILLNEED int expecting to access data in the near future
  • POSIX_FADV_DONTNEED int not expecting to access the data in the near future

Usage:

      -- Print fcntl constants supported on this host.
      for name, value in pairs (require "posix.fcntl") do
        if type (value) == "number" then
          print (name, value)
         end
      end

Tables

flock
Advisory file locks. Passed as arg to fcntl when cmd is F_GETLK, F_SETLK or F_SETLKW.

Fields:

  • l_start int starting offset
  • l_len int len = 0 means until end of file
  • l_pid int lock owner
  • l_type int lock type
  • l_whence int one of SEEK_SET, SEEK_CUR or SEEK_END
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