NAME

fcntl - file control options

SYNOPSIS

#include <fcntl.h>

DESCRIPTION

The <fcntl.h> header defines the following requests and arguments for use by the functions fcntl(2) and open(2).

Values for cmd used by fcntl (the following values are unique):

F_DUPFD

Duplicate file descriptor

F_GETFD

Get file descriptor flags

F_SETFD

Set file descriptor flags

F_GETFL

Get file status flags

F_SETFL

Set file status flags

F_GETLK

Get record locking information

F_SETLK

Set record locking information

F_SETLKW

Set record locking information; wait if blocked

File descriptor flags used for fcntl:

FD_CLOEXEC

Close the file descriptor upon execution of an exec func-

tion (see exec(2))

Values for l_type used for record locking with fcntl (the following values are unique):

F_RDLCK

Shared or read lock

F_UNLCK

Unlock

F_WRLCK

Exclusive or write lock

The following three sets of values are bitwise distinct: Values for oflag used by open:

O_CREAT

Create file if it does not exist

O_EXCL

Exclusive use flag

O_NOCTTY

Do not assign controlling tty

O_TRUNC

Truncate flag

File status flags used for open and fcntl:

O_APPEND

Set append mode

O_NDELAY

Non-blocking mode

O_NONBLOCK

Non-blocking mode (POSIX)

O_DSYNC

Write I/O operations on the file descriptor complete as

defined by synchronized I/O data integrity completion

O_RSYNC

Read I/O operations on the file descriptor complete at

the same level of integrity as specified by the the

O_DSYNC and O_SYNC flags. If both O_DSYNC and

O_RSYNC are set in oflag, all I/O operations on the file

descriptor complete as defined by synchronized I/O

data integrity completion. If both O_SYNC and

O_RSYNC are set in oflag, all I/O operations on the file

descriptor complete as defined by synchronized I/O file

integrity completion.

O_SYNC

When opening a regular file, this flag affects subsequent

writes. If set, each write(2) will wait for both the file

data and file status to be physically updated. Write I/O

operations on the file descriptor complete as defined by

synchronized I/O file integrity completion.

Mask for use with file access modes:

O_ACCMODE

Mask for file access modes

File access modes used for open and fcntl:

O_RDONLY

Open for reading only

O_RDWR

Open for reading and writing

O_WRONLY

Open for writing only

The structure flock describes a file lock. It includes the following members:

short   l_type;        /* Type of lock * /
short   l_whence;      /* Flag for starting offset * /
off_t   l_start;       /* Relative offset in bytes * /
off_t   l_len;         /* Size; if 0 then until EOF * /
long    l_sysid;       /* Returned with F_GETLK * /
pid_t   l_pid;         /* Returned with F_GETLK * /

SEE ALSO

creat(2), exec(2), fcntl(2), open(2), fsync(3C), fdatasync(3R)

NOTES

Data is successfully transferred for a write operation to a regular file when the system ensures that all data written is readable on any subsequent open of the file (even one that follows a system or power failure) in the absense of a failure of the physical storage medium.

Data is successfully transferred for a read operation when an image of the data on the physical storage medium is available to the requesting process.

Synchronized I/O data integrity completion (see fdatasync(3R)):

For reads, the operation has been completed or diagnosed if unsuccessful. The read is complete only when an image of the data has been successfully transferred to the requesting process. If there were any pending write requests affecting the data to be read at the time that the synchronized read operation was requested, these write requests will be successfully transferred prior to reading the data.

For writes, the operation has been completed or diagnosed if unsuccessful. The write is complete only when the data specified in the write request is successfully transferred, and all file system information required to retrieve the data is successfully transferred.

File attributes that are not necessary for data retrieval (access time, modification time, status change time) need not be successfully transferred prior to returning to the calling process.

Synchronized I/O file integrity completion (see fsync(3C)):

Identical to a synchronized I/O data integrity completion with the addition that all file attributes relative tothe I/O operation (including access time, modification time, status change time) will be successfully transferred prior to returning to the calling process.