// User-memory access API, modeled on Linux's <linux/uaccess.h>.
//
// Rules for kernel code touching user pointers:
//
//   1. Never dereference a user-supplied address without validating it
//      first. A syscall argument can point anywhere, including at kernel
//      memory or at nothing at all.
//
//   2. Never assume a user buffer is physically contiguous. uva2ka() only
//      translates ONE page; the direct-map alias it returns runs into an
//      unrelated physical page at the next 4K boundary. Any multi-byte
//      access through it must stay within a single page.
//
// These helpers encapsulate both rules. Because SchOS (like old x86
// without SMAP) keeps the user page table active in kernel mode, a raw
// user virtual address is directly dereferenceable once the whole range
// has been validated — that is what user_ptr() hands back, and why the
// result is safe across page boundaries where a uva2ka() pointer is not.
#ifndef SCHOS_UACCESS_H
#define SCHOS_UACCESS_H

#include "types.h"

// Nonzero if [uaddr, uaddr+size) is entirely mapped, user-accessible
// memory in the current process. size == 0 is always ok.
int access_ok(addr_t uaddr, uint64 size);

// Validate the whole range and return it as a directly usable pointer
// (the raw user VA). 0 on bad/NULL address.
void *user_ptr(addr_t uaddr, uint64 size);

// Copy between kernel and user memory, page by page.
// Return 0 on success, -EFAULT on any unmapped page.
int copy_from_user(void *dst, addr_t uaddr, uint64 n);
int copy_to_user(addr_t uaddr, const void *src, uint64 n);

// Fixed-size scalar variants, in the spirit of Linux's get_user/put_user.
#define get_user(x, uaddr)  copy_from_user(&(x), (addr_t)(uaddr), sizeof(x))
#define put_user(x, uaddr)  copy_to_user((addr_t)(uaddr), &(x), sizeof(x))

// Longest string fetchstr()/strlen_user() will scan before giving up.
#define USER_STR_MAX 32768

// Length of the NUL-terminated string at uaddr (excluding the NUL),
// validating every page it spans. -EFAULT if it runs off mapped memory
// or exceeds USER_STR_MAX.
long strlen_user(addr_t uaddr);

#endif // SCHOS_UACCESS_H