pread64

Implemented in Antinomie 0.7.0 · Syscall list

Synopsis

long pread64(unsigned int fd, char *buf, size_t count, loff_t pos);

Number (x86-64)	17
ABI	common
Kernel entry point	sys_pread64

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

Description

Reads bytes from a file descriptor at a given offset without changing the descriptor’s own offset.

Arguments

Name	Type	Meaning
fd (arg0)	unsigned int	File descriptor to operate on.
buf (arg1)	char *	Pointer to a data buffer.
count (arg2)	size_t	Number of bytes, or number of entries.
pos (arg3)	loff_t	File offset.

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.
-22	EINVAL	An argument is invalid.
-29	ESPIPE	The descriptor is not seekable, for example a pipe.

Man page

pread(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
buf (arg1)	Entry	the pointer itself, as a raw word	args.1, args.raw[1]
↳ pointee	Exit	buffer, length min(count (arg2), result), limit MAX_RW_COUNT (about 2 GiB) bytes	arg1.data	result is 0 or greater
count (arg2)	Entry	raw scalar word	args.2, args.count
pos (arg3)	Entry	raw scalar word	args.3, args.pos

Filter fields

• Result: ret, syscall.errno, syscall.success, syscall.duration_ns.
• Argument words: args.fd (arg0), args.buf (arg1), args.count (arg2), args.pos (arg3); args.0 to args.5 by position.

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.