kinit/readfile.c

/*
 * readfile.c
 *
 * Read the entire contents of a file into malloc'd storage.  This
 * is mostly useful for things like /proc files where we can't just
 * fstat() to get the length and then mmap().
 *
 * Returns the number of bytes read, or -1 on error.
 */

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <sys/stat.h>

ssize_t freadfile(FILE *f, char **pp)
{
  size_t bs;			/* Decent starting point... */
  size_t bf;			/* Bytes free */
  size_t bu = 0;		/* Bytes used */
  char *buffer, *nb;
  size_t rv;
  int old_errno = errno;
#if 0
  struct stat st;

  if ( !fstat(fileno(f), &st) && S_ISREG(st.st_mode) && st.st_size )
    bs = st.st_size+1;
  else
#endif
    bs = BUFSIZ;		/* A guess as good as any */

  bf = bs;
  buffer = malloc(bs);

  if ( !buffer )
    return -1;
  
  for (;;) {
    errno = 0;

    while ( bf && (rv = _fread(buffer+bu, bf, f)) ) {
      bu += rv;
      bf -= rv;
    }
  
    if ( errno && errno != EINTR && errno != EAGAIN ) {
      /* error */
      free(buffer);
      return -1;
    }

    if ( bf ) {
      /* Hit EOF, no error */

      /* Try to free superfluous memory */
      if ( (nb = realloc(buffer, bu+1)) )
	buffer = nb;

      /* Null-terminate result for good measure */
      buffer[bu] = '\0';

      *pp = buffer;
      errno = old_errno;
      return bu;
    }

    /* Double the size of the buffer */
    bf += bs;
    bs += bs;
    if ( !(nb = realloc(buffer, bs)) ) {
      /* out of memory error */
      free(buffer);
      return -1;
    }
    buffer = nb;
  }
}

ssize_t readfile(const char *filename, char **pp)
{
  FILE *f = fopen(filename, "r");
  ssize_t rv;

  if ( !f )
    return -1;

  rv = freadfile(f, pp);

  fclose(f);

  return rv;
}