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/* BFD library -- caching of file descriptors.

   Copyright 1990, 91, 92, 93, 94, 95, 1996 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 boolean close_one PARAMS ((void));

static 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 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 boolean

bfd_cache_delete (abfd)

     bfd *abfd;

{

  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

        boolean bfd_cache_init (bfd *abfd);

DESCRIPTION

        Add a newly opened BFD to the cache.

*/

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

        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.

*/

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 == true)

        {

          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.  */

          struct stat s;

          if (stat (abfd->filename, &s) == 0 && s.st_size != 0)

            unlink (abfd->filename);

          abfd->iostream = (PTR) fopen (abfd->filename, FOPEN_WB);

          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 (fseek ((FILE *) abfd->iostream, abfd->where, SEEK_SET) != 0)

        return NULL;

    }

  return (FILE *) abfd->iostream;

}