readv / writev / pread / pwrite - glibc

Split from the chapter glibc: stdio and Formatted I/O into the per-function layout; see the method page and the glibc ledger for coverage status.

Signature – ssize_t readv(int fd, const struct iovec *iov, int iovcnt); ssize_t writev(int fd, const struct iovec *iov, int iovcnt); ssize_t pread(int fd, void *buf, size_t count, off_t offset); ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset); – sys/uio.h for the vector pair, unistd.h for the positioned pair.

Libc side – scatter/gather and positioned I/O translate like read/write: byte counts, 0 = EOF, -1+errno. pread/pwrite add EINVAL (negative offset) and ESPIPE (unseekable) without moving the file offset. Declared under XSI gates; pread64/pwrite64 are the LFS twins (manual, Input and Output Primitives). The GNU preadv2/pwritev2 flag-taking variants (glibc gates on _GNU_SOURCE) are covered with RWF_* flags in the syscall chapter preadv2/pwritev2 entry.