fcntl

Partial in Antinomie 0.7.0 · Syscall list

Synopsis

long fcntl(unsigned int fd, unsigned int cmd, unsigned long arg);

Number (x86-64)	72
ABI	common
Kernel entry point	sys_fcntl

This is the raw kernel prototype from the pinned Linux 6.12.94 schema, not the libc wrapper.

Description

Manipulates a file descriptor: duplicating it, changing its flags, locking regions and more, selected by a command.

Arguments

Name	Type	Meaning
fd (arg0)	unsigned int	File descriptor to operate on.
cmd (arg1)	unsigned int	fcntl command (F_DUPFD, F_GETFL, F_SETLK, …).
arg (arg2)	unsigned long	Command-specific value or pointer.

Return value

On success: a command-specific value.

In an Antinomie trace the Return column and the ret filter field show the raw kernel return value. On failure that is the negative errno, for example -2 for ENOENT, not the -1 plus errno that the libc wrapper gives. syscall.errno holds the positive errno and syscall.success is false.

Common errors

Raw return	Name	Meaning
-9	EBADF	A file descriptor is not valid for this operation.
-22	EINVAL	An argument is invalid.

Man page

fcntl(2) on man7.org

Captured by Antinomie

Coverage mark: Partial. Commands that take a structure (F_SETLK, F_GETLK, F_SETOWN_EX, …) decode it. An unknown command records an fcntl.unknown_selector “no decoder” gap.

Every call is recorded as an Entry record (the six argument words and the pointees copied at entry) and an Exit record (the return value and the pointees copied at exit).

Arguments

Argument	When	How	Recorded field key	Condition
fd (arg0)	Entry	raw scalar word	args.0, args.fd
cmd (arg1)	Entry	raw scalar word	args.1, args.cmd
arg (arg2)	Entry	raw scalar word	args.2, args.arg

Filter fields

• Result: ret, syscall.errno, syscall.success, syscall.duration_ns.
• Argument words: args.fd (arg0), args.cmd (arg1), args.arg (arg2); args.0 to args.5 by position.
• Structure uid_t[2] behind arg (arg2): args.arg.<member> for value.

See Syscall Trace filter for the full syntax.

Known gaps

• Commands that take only a value (F_DUPFD, F_GETFL, F_SETFL, …) record nothing. An unknown command records fcntl.unknown_selector with the “no decoder” status.
• See the coverage mark above for the code paths that record a gap.

For what the capture statuses mean, see Capture statuses. For what is never recorded, see Known gaps.