1 /* Initialization for access to a mmap'd malloc managed region.
2 Copyright 1992 Free Software Foundation, Inc.
4 Contributed by Fred Fish at Cygnus Support. fnf@cygnus.com
6 This file is part of the GNU C Library.
8 The GNU C Library is free software; you can redistribute it and/or
9 modify it under the terms of the GNU Library General Public License as
10 published by the Free Software Foundation; either version 2 of the
11 License, or (at your option) any later version.
13 The GNU C Library is distributed in the hope that it will be useful,
14 but WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 Library General Public License for more details.
18 You should have received a copy of the GNU Library General Public
19 License along with the GNU C Library; see the file COPYING.LIB. If
20 not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
21 Boston, MA 02111-1307, USA. */
23 #include <sys/types.h>
24 #include <fcntl.h> /* After sys/types.h, at least for dpx/2. */
27 #include "mmprivate.h"
34 #if defined(HAVE_MMAP)
36 /* Forward declarations/prototypes for local functions */
38 static struct mdesc *reuse PARAMS ((int));
40 /* Initialize access to a mmalloc managed region.
42 If FD is a valid file descriptor for an open file then data for the
43 mmalloc managed region is mapped to that file, otherwise "/dev/zero"
44 is used and the data will not exist in any filesystem object.
46 If the open file corresponding to FD is from a previous use of
47 mmalloc and passes some basic sanity checks to ensure that it is
48 compatible with the current mmalloc package, then it's data is
49 mapped in and is immediately accessible at the same addresses in
50 the current process as the process that created the file.
52 If BASEADDR is not NULL, the mapping is established starting at the
53 specified address in the process address space. If BASEADDR is NULL,
54 the mmalloc package chooses a suitable address at which to start the
55 mapped region, which will be the value of the previous mapping if
56 opening an existing file which was previously built by mmalloc, or
57 for new files will be a value chosen by mmap.
59 Specifying BASEADDR provides more control over where the regions
60 start and how big they can be before bumping into existing mapped
61 regions or future mapped regions.
63 On success, returns a "malloc descriptor" which is used in subsequent
64 calls to other mmalloc package functions. It is explicitly "void *"
65 ("char *" for systems that don't fully support void) so that users
66 of the package don't have to worry about the actual implementation
69 On failure returns NULL. */
72 mmalloc_attach (fd, baseaddr)
81 /* First check to see if FD is a valid file descriptor, and if so, see
82 if the file has any current contents (size > 0). If it does, then
83 attempt to reuse the file. If we can't reuse the file, either
84 because it isn't a valid mmalloc produced file, was produced by an
85 obsolete version, or any other reason, then we fail to attach to
90 if (fstat (fd, &sbuf) < 0)
94 else if (sbuf.st_size > 0)
96 return ((PTR) reuse (fd));
100 /* We start off with the malloc descriptor allocated on the stack, until
101 we build it up enough to call _mmalloc_mmap_morecore() to allocate the
102 first page of the region and copy it there. Ensure that it is zero'd and
103 then initialize the fields that we know values for. */
106 memset ((char *) mdp, 0, sizeof (mtemp));
107 strncpy (mdp -> magic, MMALLOC_MAGIC, MMALLOC_MAGIC_SIZE);
108 mdp -> headersize = sizeof (mtemp);
109 mdp -> version = MMALLOC_VERSION;
110 mdp -> morecore = __mmalloc_mmap_morecore;
112 mdp -> base = mdp -> breakval = mdp -> top = baseaddr;
114 /* If we have not been passed a valid open file descriptor for the file
115 to map to, then open /dev/zero and use that to map to. */
119 if ((mdp -> fd = open ("/dev/zero", O_RDWR)) < 0)
125 mdp -> flags |= MMALLOC_DEVZERO;
129 /* Now try to map in the first page, copy the malloc descriptor structure
130 there, and arrange to return a pointer to this new copy. If the mapping
131 fails, then close the file descriptor if it was opened by us, and arrange
134 if ((mbase = mdp -> morecore (mdp, sizeof (mtemp))) != NULL)
136 memcpy (mbase, mdp, sizeof (mtemp));
137 mdp = (struct mdesc *) mbase;
141 if (mdp -> flags & MMALLOC_DEVZERO)
151 /* Given an valid file descriptor on an open file, test to see if that file
152 is a valid mmalloc produced file, and if so, attempt to remap it into the
153 current process at the same address to which it was previously mapped.
155 Note that we have to update the file descriptor number in the malloc-
156 descriptor read from the file to match the current valid one, before
157 trying to map the file in, and again after a successful mapping and
158 after we've switched over to using the mapped in malloc descriptor
159 rather than the temporary one on the stack.
161 Once we've switched over to using the mapped in malloc descriptor, we
162 have to update the pointer to the morecore function, since it almost
163 certainly will be at a different address if the process reusing the
164 mapped region is from a different executable.
166 Also note that if the heap being remapped previously used the mmcheckf()
167 routines, we need to update the hooks since their target functions
168 will have certainly moved if the executable has changed in any way.
169 We do this by calling mmcheckf() internally.
171 Returns a pointer to the malloc descriptor if successful, or NULL if
172 unsuccessful for some reason. */
174 static struct mdesc *
179 struct mdesc *mdp = NULL;
181 if ((lseek (fd, 0L, SEEK_SET) == 0) &&
182 (read (fd, (char *) &mtemp, sizeof (mtemp)) == sizeof (mtemp)) &&
183 (mtemp.headersize == sizeof (mtemp)) &&
184 (strcmp (mtemp.magic, MMALLOC_MAGIC) == 0) &&
185 (mtemp.version <= MMALLOC_VERSION))
188 if (__mmalloc_remap_core (&mtemp) == mtemp.base)
190 mdp = (struct mdesc *) mtemp.base;
192 mdp -> morecore = __mmalloc_mmap_morecore;
193 if (mdp -> mfree_hook != NULL)
195 mmcheckf ((PTR) mdp, (void (*) PARAMS ((void))) NULL, 1);
202 #else /* !defined (HAVE_MMAP) */
204 /* For systems without mmap, the library still supplies an entry point
205 to link to, but trying to initialize access to an mmap'd managed region
210 mmalloc_attach (fd, baseaddr)
217 #endif /* defined (HAVE_MMAP) */