#ifndef VLIBC_SYS_UIO_H
#define VLIBC_SYS_UIO_H

/*
 * vlibc — <sys/uio.h>.
 *
 * Scatter/gather I/O: readv() and writev() transfer data between a file
 * descriptor and a vector of memory buffers (POSIX.1-2008 base). Both are
 * unbuffered pass-throughs to the kernel: the iovec array is handed to
 * SYS_readv/SYS_writev as-is, and the kernel applies its own validation
 * (iovcnt in 0..IOV_MAX, iov NULL with iovcnt > 0 faults as EFAULT). Failures
 * are reported as -1 with errno set by the syscall layer.
 *
 *   Level 1 (onlyposix): readv, writev.
 *
 * The Linux extensions that build on this ABI (preadv/pwritev,
 * process_vm_readv/process_vm_writev, ...) are deliberately absent — they are
 * not POSIX and belong to a later compatibility profile.
 *
 * struct iovec matches the kernel's struct iovec (x86_64: a pointer and a
 * size_t, no padding). IOV_MAX is 1024, the Linux UIO_MAXIOV; the kernel
 * rejects any iovcnt above it with EINVAL.
 *
 * None of these declarations carry an intent attribute: every function
 * performs I/O with side effects and reports failures through errno, so
 * const/pure would be unsound.
 */

#include <vlibc/features.h>

#include <stddef.h>

#include <sys/types.h>

#ifdef __cplusplus
extern "C" {
#endif

/* Maximum number of iovec entries a single readv()/writev() call accepts. */
#define IOV_MAX 1024

/*
 * A scatter/gather segment: iov_base points at the buffer (or, for readv,
 * the buffer to fill) and iov_len is its size in bytes. Kernel layout, as
 * above.
 */
struct iovec
{
    void *iov_base; /* starting address of the segment */
    size_t iov_len; /* number of bytes in the segment */
};

/*
 * Read up to the sum of iov_len bytes from fd into the iovcnt buffers of
 * iov, in order; return the number of bytes read, 0 at end of file, or -1
 * with errno set on error. Buffers are filled completely before the next
 * one is touched.
 */
ssize_t
readv(int fd, const struct iovec *iov, int iovcnt);

/*
 * Write up to the sum of iov_len bytes from the iovcnt buffers of iov to
 * fd, in order; return the number of bytes written, or -1 with errno set
 * on error. The kernel applies its own validation (iovcnt 0..IOV_MAX, iov
 * NULL with iovcnt > 0 faults as EFAULT).
 */
ssize_t
writev(int fd, const struct iovec *iov, int iovcnt);

#ifdef __cplusplus
}
#endif

#endif /* VLIBC_SYS_UIO_H */