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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 function (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.

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