bfd/cache.c

   1 /* BFD library -- caching of file descriptors.
   2
   3    Copyright 1990, 1991, 1992, 1993, 1994, 1996, 2000, 2001, 2002,
   4    2003, 2004 Free Software Foundation, Inc.
   5
   6    Hacked by Steve Chamberlain of Cygnus Support (steve@cygnus.com).
   7
   8 This file is part of BFD, the Binary File Descriptor library.
   9
  10 This program is free software; you can redistribute it and/or modify
  11 it under the terms of the GNU General Public License as published by
  12 the Free Software Foundation; either version 2 of the License, or
  13 (at your option) any later version.
  14
  15 This program is distributed in the hope that it will be useful,
  16 but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 GNU General Public License for more details.
  19
  20 You should have received a copy of the GNU General Public License
  21 along with this program; if not, write to the Free Software
  22 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  23
  24 /*
  25 SECTION
  26         File caching
  27
  28         The file caching mechanism is embedded within BFD and allows
  29         the application to open as many BFDs as it wants without
  30         regard to the underlying operating system's file descriptor
  31         limit (often as low as 20 open files).  The module in
  32         <<cache.c>> maintains a least recently used list of
  33         <<BFD_CACHE_MAX_OPEN>> files, and exports the name
  34         <<bfd_cache_lookup>>, which runs around and makes sure that
  35         the required BFD is open. If not, then it chooses a file to
  36         close, closes it and opens the one wanted, returning its file
  37         handle.
  38
  39 */
  40
  41 #include "bfd.h"
  42 #include "sysdep.h"
  43 #include "libbfd.h"
  44
  45 static bfd_boolean bfd_cache_delete (bfd *);
  46
  47 /*
  48 INTERNAL_FUNCTION
  49         BFD_CACHE_MAX_OPEN macro
  50
  51 DESCRIPTION
  52         The maximum number of files which the cache will keep open at
  53         one time.
  54
  55 .#define BFD_CACHE_MAX_OPEN 10
  56
  57 */
  58
  59 /* The number of BFD files we have open.  */
  60
  61 static int open_files;
  62
  63 /*
  64 INTERNAL_FUNCTION
  65         bfd_last_cache
  66
  67 SYNOPSIS
  68         extern bfd *bfd_last_cache;
  69
  70 DESCRIPTION
  71         Zero, or a pointer to the topmost BFD on the chain.  This is
  72         used by the <<bfd_cache_lookup>> macro in @file{libbfd.h} to
  73         determine when it can avoid a function call.
  74 */
  75
  76 bfd *bfd_last_cache;
  77
  78 /*
  79   INTERNAL_FUNCTION
  80         bfd_cache_lookup
  81
  82   DESCRIPTION
  83         Check to see if the required BFD is the same as the last one
  84         looked up. If so, then it can use the stream in the BFD with
  85         impunity, since it can't have changed since the last lookup;
  86         otherwise, it has to perform the complicated lookup function.
  87
  88   .#define bfd_cache_lookup(x) \
  89   .    ((x)==bfd_last_cache? \
  90   .      (FILE*) (bfd_last_cache->iostream): \
  91   .       bfd_cache_lookup_worker(x))
  92
  93  */
  94
  95 /* Insert a BFD into the cache.  */
  96
  97 static void
  98 insert (bfd *abfd)
  99 {
 100   if (bfd_last_cache == NULL)
 101     {
 102       abfd->lru_next = abfd;
 103       abfd->lru_prev = abfd;
 104     }
 105   else
 106     {
 107       abfd->lru_next = bfd_last_cache;
 108       abfd->lru_prev = bfd_last_cache->lru_prev;
 109       abfd->lru_prev->lru_next = abfd;
 110       abfd->lru_next->lru_prev = abfd;
 111     }
 112   bfd_last_cache = abfd;
 113 }
 114
 115 /* Remove a BFD from the cache.  */
 116
 117 static void
 118 snip (bfd *abfd)
 119 {
 120   abfd->lru_prev->lru_next = abfd->lru_next;
 121   abfd->lru_next->lru_prev = abfd->lru_prev;
 122   if (abfd == bfd_last_cache)
 123     {
 124       bfd_last_cache = abfd->lru_next;
 125       if (abfd == bfd_last_cache)
 126         bfd_last_cache = NULL;
 127     }
 128 }
 129
 130 /* We need to open a new file, and the cache is full.  Find the least
 131    recently used cacheable BFD and close it.  */
 132
 133 static bfd_boolean
 134 close_one (void)
 135 {
 136   register bfd *kill;
 137
 138   if (bfd_last_cache == NULL)
 139     kill = NULL;
 140   else
 141     {
 142       for (kill = bfd_last_cache->lru_prev;
 143            ! kill->cacheable;
 144            kill = kill->lru_prev)
 145         {
 146           if (kill == bfd_last_cache)
 147             {
 148               kill = NULL;
 149               break;
 150             }
 151         }
 152     }
 153
 154   if (kill == NULL)
 155     {
 156       /* There are no open cacheable BFD's.  */
 157       return TRUE;
 158     }
 159
 160   kill->where = real_ftell ((FILE *) kill->iostream);
 161
 162   return bfd_cache_delete (kill);
 163 }
 164
 165 /* Close a BFD and remove it from the cache.  */
 166
 167 static bfd_boolean
 168 bfd_cache_delete (bfd *abfd)
 169 {
 170   bfd_boolean ret;
 171
 172   if (fclose ((FILE *) abfd->iostream) == 0)
 173     ret = TRUE;
 174   else
 175     {
 176       ret = FALSE;
 177       bfd_set_error (bfd_error_system_call);
 178     }
 179
 180   snip (abfd);
 181
 182   abfd->iostream = NULL;
 183   --open_files;
 184
 185   return ret;
 186 }
 187
 188 /*
 189 INTERNAL_FUNCTION
 190         bfd_cache_init
 191
 192 SYNOPSIS
 193         bfd_boolean bfd_cache_init (bfd *abfd);
 194
 195 DESCRIPTION
 196         Add a newly opened BFD to the cache.
 197 */
 198
 199 bfd_boolean
 200 bfd_cache_init (bfd *abfd)
 201 {
 202   BFD_ASSERT (abfd->iostream != NULL);
 203   if (open_files >= BFD_CACHE_MAX_OPEN)
 204     {
 205       if (! close_one ())
 206         return FALSE;
 207     }
 208   insert (abfd);
 209   ++open_files;
 210   return TRUE;
 211 }
 212
 213 /*
 214 INTERNAL_FUNCTION
 215         bfd_cache_close
 216
 217 SYNOPSIS
 218         bfd_boolean bfd_cache_close (bfd *abfd);
 219
 220 DESCRIPTION
 221         Remove the BFD @var{abfd} from the cache. If the attached file is open,
 222         then close it too.
 223
 224 RETURNS
 225         <<FALSE>> is returned if closing the file fails, <<TRUE>> is
 226         returned if all is well.
 227 */
 228
 229 bfd_boolean
 230 bfd_cache_close (bfd *abfd)
 231 {
 232   if (abfd->iostream == NULL
 233       || (abfd->flags & BFD_IN_MEMORY) != 0)
 234     return TRUE;
 235
 236   return bfd_cache_delete (abfd);
 237 }
 238
 239 /*
 240 INTERNAL_FUNCTION
 241         bfd_open_file
 242
 243 SYNOPSIS
 244         FILE* bfd_open_file (bfd *abfd);
 245
 246 DESCRIPTION
 247         Call the OS to open a file for @var{abfd}.  Return the <<FILE *>>
 248         (possibly <<NULL>>) that results from this operation.  Set up the
 249         BFD so that future accesses know the file is open. If the <<FILE *>>
 250         returned is <<NULL>>, then it won't have been put in the
 251         cache, so it won't have to be removed from it.
 252 */
 253
 254 FILE *
 255 bfd_open_file (bfd *abfd)
 256 {
 257   abfd->cacheable = TRUE;       /* Allow it to be closed later.  */
 258
 259   if (open_files >= BFD_CACHE_MAX_OPEN)
 260     {
 261       if (! close_one ())
 262         return NULL;
 263     }
 264
 265   switch (abfd->direction)
 266     {
 267     case read_direction:
 268     case no_direction:
 269       abfd->iostream = (PTR) fopen (abfd->filename, FOPEN_RB);
 270       break;
 271     case both_direction:
 272     case write_direction:
 273       if (abfd->opened_once)
 274         {
 275           abfd->iostream = (PTR) fopen (abfd->filename, FOPEN_RUB);
 276           if (abfd->iostream == NULL)
 277             abfd->iostream = (PTR) fopen (abfd->filename, FOPEN_WUB);
 278         }
 279       else
 280         {
 281           /* Create the file.
 282
 283              Some operating systems won't let us overwrite a running
 284              binary.  For them, we want to unlink the file first.
 285
 286              However, gcc 2.95 will create temporary files using
 287              O_EXCL and tight permissions to prevent other users from
 288              substituting other .o files during the compilation.  gcc
 289              will then tell the assembler to use the newly created
 290              file as an output file.  If we unlink the file here, we
 291              open a brief window when another user could still
 292              substitute a file.
 293
 294              So we unlink the output file if and only if it has
 295              non-zero size.  */
 296 #ifndef __MSDOS__
 297           /* Don't do this for MSDOS: it doesn't care about overwriting
 298              a running binary, but if this file is already open by
 299              another BFD, we will be in deep trouble if we delete an
 300              open file.  In fact, objdump does just that if invoked with
 301              the --info option.  */
 302           struct stat s;
 303
 304           if (stat (abfd->filename, &s) == 0 && s.st_size != 0)
 305             unlink (abfd->filename);
 306 #endif
 307           abfd->iostream = (PTR) fopen (abfd->filename, FOPEN_WUB);
 308           abfd->opened_once = TRUE;
 309         }
 310       break;
 311     }
 312
 313   if (abfd->iostream != NULL)
 314     {
 315       if (! bfd_cache_init (abfd))
 316         return NULL;
 317     }
 318
 319   return (FILE *) abfd->iostream;
 320 }
 321
 322 /*
 323 INTERNAL_FUNCTION
 324         bfd_cache_lookup_worker
 325
 326 SYNOPSIS
 327         FILE *bfd_cache_lookup_worker (bfd *abfd);
 328
 329 DESCRIPTION
 330         Called when the macro <<bfd_cache_lookup>> fails to find a
 331         quick answer.  Find a file descriptor for @var{abfd}.  If
 332         necessary, it open it.  If there are already more than
 333         <<BFD_CACHE_MAX_OPEN>> files open, it tries to close one first, to
 334         avoid running out of file descriptors.
 335 */
 336
 337 FILE *
 338 bfd_cache_lookup_worker (bfd *abfd)
 339 {
 340   if ((abfd->flags & BFD_IN_MEMORY) != 0)
 341     abort ();
 342
 343   if (abfd->my_archive)
 344     abfd = abfd->my_archive;
 345
 346   if (abfd->iostream != NULL)
 347     {
 348       /* Move the file to the start of the cache.  */
 349       if (abfd != bfd_last_cache)
 350         {
 351           snip (abfd);
 352           insert (abfd);
 353         }
 354     }
 355   else
 356     {
 357       if (bfd_open_file (abfd) == NULL)
 358         return NULL;
 359       if (abfd->where != (unsigned long) abfd->where)
 360         return NULL;
 361       if (real_fseek ((FILE *) abfd->iostream, abfd->where, SEEK_SET) != 0)
 362         return NULL;
 363     }
 364
 365   return (FILE *) abfd->iostream;
 366 }