fcntl.2 (2011 03)

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fcntl(2) fcntl(2)

NAME

fcntl() - ﬁle control

SYNOPSIS

#include <fcntl.h>

int fcntl(int ﬁldes, int cmd, ... /* arg */);

Remarks

The ANSI C ", ..." construct denotes a variable length argument list whose optional [or required]

members are given in the associated comment (

/* */).

DESCRIPTION

fcntl() provides for control over open ﬁles. ﬁldes is an open ﬁle descriptor.

The following are possible values for the cmd argument:

F_ADVISE Fadvise service request (see fadvise (2)).

F_DUPFD Return a new ﬁle descriptor having the following characteristics:

• Lowest numbered available ﬁle descriptor greater than or equal to the third

argument, arg , taken as an integer of type

int.

• Same open ﬁle (or pipe) as the original ﬁle.

• Same ﬁle pointer as the original ﬁle (that is, both ﬁle descriptors share one ﬁle

pointer).

• Same access mode (read, write or read/write).

• Same ﬁle status ﬂags (that is, both ﬁle descriptors share the same ﬁle status

ﬂags).

• The close-on-exec ﬂag associated with the new ﬁle descriptor is set to remain

open across

exec() system calls.

F_GETFD Get the ﬁle descriptor ﬂags (deﬁned in <fcntl.h>) that are associated with the

ﬁle descriptor ﬁldes . File descriptor ﬂags are associated with a single ﬁle descriptor

and do not affect other ﬁle descriptors that refer to the same ﬁle.

F_SETFD Set the ﬁle descriptor ﬂags (deﬁned in <fcntl.h>) that are associated with ﬁldes ,

to the third argument, arg , taken as an integer of type

int (see F_GETFD). If the

FD_CLOEXEC ﬂag in the third argument is 0, the ﬁle will remain open across

exec(); otherwise, the ﬁle will be closed upon execution of exec().

F_CLOSEM Close all open ﬁle descriptors greater than or equal to ﬁldes .

F_GETFL Get ﬁle status ﬂags and access modes; see fcntl (5).

F_SETFL Set ﬁle status ﬂags to the third argument, arg, taken as an integer of type int.

Only certain ﬂags can be set; see fcntl (5). It is not possible to set both O_NDELAY

and O_NONBLOCK.

F_GETLK Get the ﬁrst lock that blocks the lock described by the variable of type struct

flock pointed to by the third argument, arg , taken as a pointer to type struct

flock. The information retrieved overwrites the information passed to fcntl()

in the flock structure. If no lock is found that would prevent this lock from being

created, the structure is passed back unchanged, except that the lock type is set to

F_UNLCK.

F_SETLK Set or clear a ﬁle segment lock according to the variable of type struct flock

pointed to by the third argument, arg, taken as a pointer to type struct flock

(see fcntl (5)). The cmd F_SETLK is used to establish read ( F_RDLCK ) and write

( F_WRLCK ) locks, as well as to remove either type of lock ( F_UNLCK ). If a read or

write lock cannot be set, fcntl() returns immediately with an error value of −1.

F_SETLKW This cmd is the same as F_SETLK except that if a read or write lock is blocked by

other locks, the process will sleep until the segment is free to be locked.

F_GETLK64 Same as F_GETLK, except arg is a pointer to struct flock64 instead of

struct flock.

HP-UX 11i Version 3: March 2011 − 1 − Hewlett-Packard Company 1

Summary of content (8 pages)

PAGE 1
fcntl(2) fcntl(2) NAME fcntl() - file control SYNOPSIS #include int fcntl(int fildes, int cmd, ... /* arg */); Remarks The ANSI C ", ..." construct denotes a variable length argument list whose optional [or required] members are given in the associated comment (/* */). DESCRIPTION fcntl() provides for control over open files. fildes is an open file descriptor. The following are possible values for the cmd argument: F_ADVISE Fadvise service request (see fadvise (2)).
PAGE 2
fcntl(2) fcntl(2) F_SETLK64 Same as F_SETLK, except arg is a pointer to struct flock64 instead of struct flock. F_SETLKW64 Same as F_SETLKW, except arg is a pointer to struct flock64 instead of struct flock. F_GETOWN If fildes refers to a socket, fcntl() returns the process or process group ID specified to receive SIGURG signals when out-of-band data is available. Positive values indicate a process ID; negative values, other than -1, indicate a process group ID.
PAGE 3
fcntl(2) fcntl(2) F_SHARE Sets a share reservation on a file with the specified access mode and designates which types of access to deny. The details of the file share reservation request are specified using the third argument arg, which should be a pointer to a struct fshare (defined in ). See the File Share Reservations section below. F_UNSHARE Removes an existing share reservation.
PAGE 4
fcntl(2) fcntl(2) File Share Reservations File share reservations are an advisory form of access control among cooperating processes, on both local and remote machines. File share reservations are most commonly used by DOS or Windows emulators and DOS based NFS clients. The fcntl() system call can be used to set file share reservations using the F_SHARE command. A share reservation is described by an fshare structure defined in
PAGE 5
fcntl(2) fcntl(2) The structure oplock describes the details of the lock being requested on the opened file descriptor. If the command succeeds, it also contains the owner ID (o_owner) of the process as well as the type of oplock (o_type) being requested. The o_sysid can also be specified. The process ID (o_pid) is the requesting process with which to associate the oplock. Optional flags o_flags, o_timeout, and signal value (o_sig_val) can also be specified.
PAGE 6
fcntl(2) fcntl(2) RETURN VALUE Upon successful completion, the value returned depends on cmd as follows: A fA F_ADVISE Value of requested hint operation. F_DUPFD A new file descriptor. F_GETFD Value of close-on-exec flag (only the low-order bit is defined). F_SETFD Value other than −1. F_GETFL Value of file status flags and access modes. F_SETFL Value other than −1. F_GETLK Value other than −1. F_SETLK Value other than −1. F_SETLKW Value other than −1.
PAGE 7
fcntl(2) fcntl(2) [EFAULT] cmd is either F_GETLK, F_SETLK, or F_SETLKW, and arg points to an illegal address. [EFAULT] cmd is either F_SHARE or F_UNSHARE, and arg points to an illegal address. [EFAULT] cmd [EINTR] cmd is F_SETLKW and the call was interrupted by a signal. [EINVAL] cmd is F_DUPFD and arg is negative. [EINVAL] cmd is F_GETLK, F_SETLK, or F_SETLKW, and arg or the data it points to is not valid, or fildes refers to a file that does not support locking.
PAGE 8
fcntl(2) fcntl(2) 2. Any error encountered is reported only for closing fildes . Errors encountered while closing file descriptors greater than fildes are ignored. AUTHOR fcntl() was developed by HP, AT&T and the University of California, Berkeley. SEE ALSO lockd(1M), statd(1M), chmod(2), close(2), creat(2), creat64(2), exec(2), fadvise(2), lockf(2), open(2), read(2), truncate(2), write(2), fcntl(5). STANDARDS CONFORMANCE fcntl(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.