writev

Implemented in Antinomie 0.7.0 · Syscall list

Synopsis

long writev(unsigned long fd, const struct iovec *vec, unsigned long vlen);

Number (x86-64)	20
ABI	64
Kernel entry point	sys_writev

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

Description

Writes from several buffers described by an array of iovec structures to a file descriptor.

Arguments

Name	Type	Meaning
fd (arg0)	unsigned long	File descriptor to operate on.
vec (arg1)	const struct iovec *	Pointer to an array of iovec structures.
vlen (arg2)	unsigned long	Number of messages or vector entries.

Return value

On success: The number of bytes transferred (see the description for what 0 means).

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.
-14	EFAULT	A pointer argument points outside the accessible address space.
-22	EINVAL	An argument is invalid.

Man page

writev(2) on man7.org

Captured by Antinomie

Coverage mark: Implemented. Every pointer argument has a capture rule in the pinned kernel patch and none of them records a “no decoder”, “address only” or “not observed” gap on any code path. Individual values can still be incomplete on a particular call; see the capture statuses.

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
vec (arg1)	Entry	the pointer itself, as a raw word	args.1, args.raw[1]
↳ pointee	Entry	array of iovec structures, count from vlen (arg2), at most 1,024 entries	arg1.iov	always
↳ pointee	Entry	each buffer, its length taken from the iovec, total capped at MAX_RW_COUNT	arg1.iov[i].data	always
vlen (arg2)	Entry	raw scalar word	args.2, args.vlen

Filter fields

• Result: ret, syscall.errno, syscall.success, syscall.duration_ns.
• Argument words: args.fd (arg0), args.vec (arg1), args.vlen (arg2); args.0 to args.5 by position.
• Structure iovec[] behind vec (arg1): args.vec.<member> for iov_base, iov_len.

See Syscall Trace filter for the full syntax.

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