mmalloc/attach.c

   1 /* Initialization for access to a mmap'd malloc managed region.
   2    Copyright 1992 Free Software Foundation, Inc.
   3
   4    Contributed by Fred Fish at Cygnus Support.   fnf@cygnus.com
   5
   6 This program is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2 of the License, or
   9 (at your option) any later version.
  10
  11 This program is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with this program; if not, write to the Free Software
  18 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  19
  20
  21 #include <fcntl.h>
  22 #include <sys/types.h>
  23 #include <sys/stat.h>
  24 #include <string.h>
  25 #include "mmalloc.h"
  26
  27 #ifndef SEEK_SET
  28 #define SEEK_SET 0
  29 #endif
  30
  31
  32 #if defined(HAVE_MMAP)
  33
  34 /* Forward declarations/prototypes for local functions */
  35
  36 static struct mdesc *reuse PARAMS ((int));
  37
  38 /* Initialize access to a mmalloc managed region.
  39
  40    If FD is a valid file descriptor for an open file then data for the
  41    mmalloc managed region is mapped to that file, otherwise "/dev/zero"
  42    is used and the data will not exist in any filesystem object.
  43
  44    If the open file corresponding to FD is from a previous use of
  45    mmalloc and passes some basic sanity checks to ensure that it is
  46    compatible with the current mmalloc package, then it's data is
  47    mapped in and is immediately accessible at the same addresses in
  48    the current process as the process that created the file.
  49
  50    If BASEADDR is not NULL, the mapping is established starting at the
  51    specified address in the process address space.  If BASEADDR is NULL,
  52    the mmalloc package chooses a suitable address at which to start the
  53    mapped region, which will be the value of the previous mapping if
  54    opening an existing file which was previously built by mmalloc, or
  55    for new files will be a value chosen by mmap.
  56
  57    Specifying BASEADDR provides more control over where the regions
  58    start and how big they can be before bumping into existing mapped
  59    regions or future mapped regions.
  60
  61    On success, returns a "malloc descriptor" which is used in subsequent
  62    calls to other mmalloc package functions.  It is explicitly "void *"
  63    ("char *" for systems that don't fully support void) so that users
  64    of the package don't have to worry about the actual implementation
  65    details.
  66
  67    On failure returns NULL. */
  68
  69 PTR
  70 mmalloc_attach (fd, baseaddr)
  71   int fd;
  72   PTR baseaddr;
  73 {
  74   struct mdesc mtemp;
  75   struct mdesc *mdp;
  76   PTR mbase;
  77   struct stat sbuf;
  78
  79   /* First check to see if FD is a valid file descriptor, and if so, see
  80      if the file has any current contents (size > 0).  If it does, then
  81      attempt to reuse the file.  If we can't reuse the file, either
  82      because it isn't a valid mmalloc produced file, was produced by an
  83      obsolete version, or any other reason, then we fail to attach to
  84      this file. */
  85
  86   if (fd >= 0)
  87     {
  88       if (fstat (fd, &sbuf) < 0)
  89         {
  90           return (NULL);
  91         }
  92       else if (sbuf.st_size > 0)
  93         {
  94           return ((PTR) reuse (fd));
  95         }
  96     }
  97
  98   /* We start off with the malloc descriptor allocated on the stack, until
  99      we build it up enough to call _mmalloc_mmap_morecore() to allocate the
 100      first page of the region and copy it there.  Ensure that it is zero'd and
 101      then initialize the fields that we know values for. */
 102
 103   mdp = &mtemp;
 104   (void) memset ((char *) mdp, 0, sizeof (mtemp));
 105   (void) strncpy (mdp -> magic, MMALLOC_MAGIC, MMALLOC_MAGIC_SIZE);
 106   mdp -> headersize = sizeof (mtemp);
 107   mdp -> version = MMALLOC_VERSION;
 108   mdp -> morecore = __mmalloc_mmap_morecore;
 109   mdp -> fd = fd;
 110   mdp -> base = mdp -> breakval = mdp -> top = baseaddr;
 111
 112   /* If we have not been passed a valid open file descriptor for the file
 113      to map to, then open /dev/zero and use that to map to. */
 114
 115   if (mdp -> fd < 0)
 116     {
 117       if ((mdp -> fd = open ("/dev/zero", O_RDWR)) < 0)
 118         {
 119           return (NULL);
 120         }
 121       else
 122         {
 123           mdp -> flags |= MMALLOC_DEVZERO;
 124         }
 125     }
 126
 127   /*  Now try to map in the first page, copy the malloc descriptor structure
 128       there, and arrange to return a pointer to this new copy.  If the mapping
 129       fails, then close the file descriptor if it was opened by us, and arrange
 130       to return a NULL. */
 131
 132   if ((mbase = mdp -> morecore (mdp, sizeof (mtemp))) != NULL)
 133     {
 134       (void) memcpy (mbase, mdp, sizeof (mtemp));
 135       mdp = (struct mdesc *) mbase;
 136     }
 137   else
 138     {
 139       if (mdp -> flags & MMALLOC_DEVZERO)
 140         {
 141           close (mdp -> fd);
 142         }
 143       mdp = NULL;
 144     }
 145
 146   return ((PTR) mdp);
 147 }
 148
 149 /* Given an valid file descriptor on an open file, test to see if that file
 150    is a valid mmalloc produced file, and if so, attempt to remap it into the
 151    current process at the same address to which it was previously mapped.
 152
 153    Note that we have to update the file descriptor number in the malloc-
 154    descriptor read from the file to match the current valid one, before
 155    trying to map the file in, and again after a successful mapping and
 156    after we've switched over to using the mapped in malloc descriptor
 157    rather than the temporary one on the stack.
 158
 159    Once we've switched over to using the mapped in malloc descriptor, we
 160    have to update the pointer to the morecore function, since it almost
 161    certainly will be at a different address if the process reusing the
 162    mapped region is from a different executable.
 163
 164    Also note that if the heap being remapped previously used the mmcheck()
 165    routines, we need to update the hooks since their target functions
 166    will have certainly moved if the executable has changed in any way.
 167    We do this by calling mmcheck() internally.
 168
 169    Returns a pointer to the malloc descriptor if successful, or NULL if
 170    unsuccessful for some reason. */
 171
 172 static struct mdesc *
 173 reuse (fd)
 174   int fd;
 175 {
 176   struct mdesc mtemp;
 177   struct mdesc *mdp = NULL;
 178
 179   if ((lseek (fd, 0L, SEEK_SET) == 0) &&
 180       (read (fd, (char *) &mtemp, sizeof (mtemp)) == sizeof (mtemp)) &&
 181       (mtemp.headersize == sizeof (mtemp)) &&
 182       (strcmp (mtemp.magic, MMALLOC_MAGIC) == 0) &&
 183       (mtemp.version <= MMALLOC_VERSION))
 184     {
 185       mtemp.fd = fd;
 186       if (__mmalloc_remap_core (&mtemp) == mtemp.base)
 187         {
 188           mdp = (struct mdesc *) mtemp.base;
 189           mdp -> fd = fd;
 190           mdp -> morecore = __mmalloc_mmap_morecore;
 191           if (mdp -> mfree_hook != NULL)
 192             {
 193               (void) mmcheck ((PTR) mdp, (void (*) PARAMS ((void))) NULL);
 194             }
 195         }
 196     }
 197   return (mdp);
 198 }
 199
 200 #else   /* !defined (HAVE_MMAP) */
 201
 202 /* For systems without mmap, the library still supplies an entry point
 203    to link to, but trying to initialize access to an mmap'd managed region
 204    always fails. */
 205
 206 /* ARGSUSED */
 207 PTR
 208 mmalloc_attach (fd, baseaddr)
 209   int fd;
 210   PTR baseaddr;
 211 {
 212    return (NULL);
 213 }
 214
 215 #endif  /* defined (HAVE_MMAP) */
 216