source: trunk/binutils/bfd/cache.c@ 2840

/* BFD library -- caching of file descriptors.
   Copyright 1990, 1991, 1992, 1993, 1994, 1996, 2000, 2001, 2002
   Free Software Foundation, Inc.
   Hacked by Steve Chamberlain of Cygnus Support (steve@cygnus.com).

This file is part of BFD, the Binary File Descriptor library.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/*
SECTION
        File caching

        The file caching mechanism is embedded within BFD and allows
        the application to open as many BFDs as it wants without
        regard to the underlying operating system's file descriptor
        limit (often as low as 20 open files).  The module in
        <<cache.c>> maintains a least recently used list of
        <<BFD_CACHE_MAX_OPEN>> files, and exports the name
        <<bfd_cache_lookup>>, which runs around and makes sure that
        the required BFD is open. If not, then it chooses a file to
        close, closes it and opens the one wanted, returning its file
        handle.

*/

#include "bfd.h"
#include "sysdep.h"
#include "libbfd.h"

static void insert PARAMS ((bfd *));
static void snip PARAMS ((bfd *));
static bfd_boolean close_one PARAMS ((void));
static bfd_boolean bfd_cache_delete PARAMS ((bfd *));

/*
INTERNAL_FUNCTION
        BFD_CACHE_MAX_OPEN macro

DESCRIPTION
        The maximum number of files which the cache will keep open at
        one time.

.#define BFD_CACHE_MAX_OPEN 10

*/

/* The number of BFD files we have open.  */

static int open_files;

/*
INTERNAL_FUNCTION
        bfd_last_cache

SYNOPSIS
        extern bfd *bfd_last_cache;

DESCRIPTION
        Zero, or a pointer to the topmost BFD on the chain.  This is
        used by the <<bfd_cache_lookup>> macro in @file{libbfd.h} to
        determine when it can avoid a function call.
*/

bfd *bfd_last_cache;

/*
  INTERNAL_FUNCTION
        bfd_cache_lookup

  DESCRIPTION
        Check to see if the required BFD is the same as the last one
        looked up. If so, then it can use the stream in the BFD with
        impunity, since it can't have changed since the last lookup;
        otherwise, it has to perform the complicated lookup function.

  .#define bfd_cache_lookup(x) \
  .    ((x)==bfd_last_cache? \
  .      (FILE*) (bfd_last_cache->iostream): \
  .       bfd_cache_lookup_worker(x))

 */

/* Insert a BFD into the cache.  */

static INLINE void
insert (abfd)
     bfd *abfd;
{
  if (bfd_last_cache == NULL)
    {
      abfd->lru_next = abfd;
      abfd->lru_prev = abfd;
    }
  else
    {
      abfd->lru_next = bfd_last_cache;
      abfd->lru_prev = bfd_last_cache->lru_prev;
      abfd->lru_prev->lru_next = abfd;
      abfd->lru_next->lru_prev = abfd;
    }
  bfd_last_cache = abfd;
}

/* Remove a BFD from the cache.  */

static INLINE void
snip (abfd)
     bfd *abfd;
{
  abfd->lru_prev->lru_next = abfd->lru_next;
  abfd->lru_next->lru_prev = abfd->lru_prev;
  if (abfd == bfd_last_cache)
    {
      bfd_last_cache = abfd->lru_next;
      if (abfd == bfd_last_cache)
        bfd_last_cache = NULL;
    }
}

/* We need to open a new file, and the cache is full.  Find the least
   recently used cacheable BFD and close it.  */

static bfd_boolean
close_one ()
{
  register bfd *kill;

  if (bfd_last_cache == NULL)
    kill = NULL;
  else
    {
      for (kill = bfd_last_cache->lru_prev;
           ! kill->cacheable;
           kill = kill->lru_prev)
        {
          if (kill == bfd_last_cache)
            {
              kill = NULL;
              break;
            }
        }
    }

  if (kill == NULL)
    {
      /* There are no open cacheable BFD's.  */
      return TRUE;
    }

  kill->where = ftell ((FILE *) kill->iostream);

  return bfd_cache_delete (kill);
}

/* Close a BFD and remove it from the cache.  */

static bfd_boolean
bfd_cache_delete (abfd)
     bfd *abfd;
{
  bfd_boolean ret;

  if (fclose ((FILE *) abfd->iostream) == 0)
    ret = TRUE;
  else
    {
      ret = FALSE;
      bfd_set_error (bfd_error_system_call);
    }

  snip (abfd);

  abfd->iostream = NULL;
  --open_files;

  return ret;
}

/*
INTERNAL_FUNCTION
        bfd_cache_init

SYNOPSIS
        bfd_boolean bfd_cache_init (bfd *abfd);

DESCRIPTION
        Add a newly opened BFD to the cache.
*/

bfd_boolean
bfd_cache_init (abfd)
     bfd *abfd;
{
  BFD_ASSERT (abfd->iostream != NULL);
  if (open_files >= BFD_CACHE_MAX_OPEN)
    {
      if (! close_one ())
        return FALSE;
    }
  insert (abfd);
  ++open_files;
  return TRUE;
}

/*
INTERNAL_FUNCTION
        bfd_cache_close

SYNOPSIS
        bfd_boolean bfd_cache_close (bfd *abfd);

DESCRIPTION
        Remove the BFD @var{abfd} from the cache. If the attached file is open,
        then close it too.

RETURNS
        <<FALSE>> is returned if closing the file fails, <<TRUE>> is
        returned if all is well.
*/

bfd_boolean
bfd_cache_close (abfd)
     bfd *abfd;
{
  if (abfd->iostream == NULL
      || (abfd->flags & BFD_IN_MEMORY) != 0)
    return TRUE;

  return bfd_cache_delete (abfd);
}

/*
INTERNAL_FUNCTION
        bfd_open_file

SYNOPSIS
        FILE* bfd_open_file(bfd *abfd);

DESCRIPTION
        Call the OS to open a file for @var{abfd}.  Return the <<FILE *>>
        (possibly <<NULL>>) that results from this operation.  Set up the
        BFD so that future accesses know the file is open. If the <<FILE *>>
        returned is <<NULL>>, then it won't have been put in the
        cache, so it won't have to be removed from it.
*/

FILE *
bfd_open_file (abfd)
     bfd *abfd;
{
  abfd->cacheable = TRUE;       /* Allow it to be closed later.  */

  if (open_files >= BFD_CACHE_MAX_OPEN)
    {
      if (! close_one ())
        return NULL;
    }

  switch (abfd->direction)
    {
    case read_direction:
    case no_direction:
      abfd->iostream = (PTR) fopen (abfd->filename, FOPEN_RB);
      break;
    case both_direction:
    case write_direction:
      if (abfd->opened_once)
        {
          abfd->iostream = (PTR) fopen (abfd->filename, FOPEN_RUB);
          if (abfd->iostream == NULL)
            abfd->iostream = (PTR) fopen (abfd->filename, FOPEN_WUB);
        }
      else
        {
          /* Create the file.

             Some operating systems won't let us overwrite a running
             binary.  For them, we want to unlink the file first.

             However, gcc 2.95 will create temporary files using
             O_EXCL and tight permissions to prevent other users from
             substituting other .o files during the compilation.  gcc
             will then tell the assembler to use the newly created
             file as an output file.  If we unlink the file here, we
             open a brief window when another user could still
             substitute a file.

             So we unlink the output file if and only if it has
             non-zero size.  */
#ifndef __MSDOS__
          /* Don't do this for MSDOS: it doesn't care about overwriting
             a running binary, but if this file is already open by
             another BFD, we will be in deep trouble if we delete an
             open file.  In fact, objdump does just that if invoked with
             the --info option.  */
          struct stat s;

          if (stat (abfd->filename, &s) == 0 && s.st_size != 0)
            unlink (abfd->filename);
#endif
          abfd->iostream = (PTR) fopen (abfd->filename, FOPEN_WUB);
          abfd->opened_once = TRUE;
        }
      break;
    }

  if (abfd->iostream != NULL)
    {
      if (! bfd_cache_init (abfd))
        return NULL;
    }

  return (FILE *) abfd->iostream;
}

/*
INTERNAL_FUNCTION
        bfd_cache_lookup_worker

SYNOPSIS
        FILE *bfd_cache_lookup_worker(bfd *abfd);

DESCRIPTION
        Called when the macro <<bfd_cache_lookup>> fails to find a
        quick answer.  Find a file descriptor for @var{abfd}.  If
        necessary, it open it.  If there are already more than
        <<BFD_CACHE_MAX_OPEN>> files open, it tries to close one first, to
        avoid running out of file descriptors.
*/

FILE *
bfd_cache_lookup_worker (abfd)
     bfd *abfd;
{
  if ((abfd->flags & BFD_IN_MEMORY) != 0)
    abort ();

  if (abfd->my_archive)
    abfd = abfd->my_archive;

  if (abfd->iostream != NULL)
    {
      /* Move the file to the start of the cache.  */
      if (abfd != bfd_last_cache)
        {
          snip (abfd);
          insert (abfd);
        }
    }
  else
    {
      if (bfd_open_file (abfd) == NULL)
        return NULL;
      if (abfd->where != (unsigned long) abfd->where)
        return NULL;
      if (fseek ((FILE *) abfd->iostream, (long) abfd->where, SEEK_SET) != 0)
        return NULL;
    }

  return (FILE *) abfd->iostream;
}