fusl/src/stdio/__stdio_read.c

#include "stdio_impl.h"
#include <sys/uio.h>

size_t __stdio_read(FILE* f, unsigned char* buf, size_t len) {
  struct iovec iov[2] = {{.iov_base = buf, .iov_len = len - !!f->buf_size},
                         {.iov_base = f->buf, .iov_len = f->buf_size}};
  ssize_t cnt;

  cnt = syscall(SYS_readv, f->fd, iov, 2);
  if (cnt <= 0) {
    f->flags |= F_EOF ^ ((F_ERR ^ F_EOF) & cnt);
    return cnt;
  }
  if (cnt <= iov[0].iov_len)
    return cnt;
  cnt -= iov[0].iov_len;
  f->rpos = f->buf;
  f->rend = f->buf + cnt;
  if (f->buf_size)
    buf[len - 1] = *f->rpos++;
  return len;
}