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/* Initialization for access to a mmap'd malloc managed region.
Copyright 1992 Free Software Foundation, Inc.
Contributed by Fred Fish at Cygnus Support. fnf@cygnus.com
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., 675 Mass Ave, Cambridge, MA 02139, USA. */
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#include "mmalloc.h"
#ifndef SEEK_SET
#define SEEK_SET 0
#endif
#if defined(HAVE_MMAP)
/* Forward declarations/prototypes for local functions */
static struct mdesc *reuse PARAMS ((int));
/* Initialize access to a mmalloc managed region.
If FD is a valid file descriptor for an open file then data for the
mmalloc managed region is mapped to that file, otherwise "/dev/zero"
is used and the data will not exist in any filesystem object.
If the open file corresponding to FD is from a previous use of
mmalloc and passes some basic sanity checks to ensure that it is
compatible with the current mmalloc package, then it's data is
mapped in and is immediately accessible at the same addresses in
the current process as the process that created the file.
If BASEADDR is not NULL, the mapping is established starting at the
specified address in the process address space. If BASEADDR is NULL,
the mmalloc package chooses a suitable address at which to start the
mapped region, which will be the value of the previous mapping if
opening an existing file which was previously built by mmalloc, or
for new files will be a value chosen by mmap.
Specifying BASEADDR provides more control over where the regions
start and how big they can be before bumping into existing mapped
regions or future mapped regions.
On success, returns a "malloc descriptor" which is used in subsequent
calls to other mmalloc package functions. It is explicitly "void *"
("char *" for systems that don't fully support void) so that users
of the package don't have to worry about the actual implementation
details.
On failure returns NULL. */
PTR
mmalloc_attach (fd, baseaddr)
int fd;
PTR baseaddr;
{
struct mdesc mtemp;
struct mdesc *mdp;
PTR mbase;
struct stat sbuf;
/* First check to see if FD is a valid file descriptor, and if so, see
if the file has any current contents (size > 0). If it does, then
attempt to reuse the file. If we can't reuse the file, either
because it isn't a valid mmalloc produced file, was produced by an
obsolete version, or any other reason, then we fail to attach to
this file. */
if (fd >= 0)
{
if (fstat (fd, &sbuf) < 0)
{
return (NULL);
}
else if (sbuf.st_size > 0)
{
return ((PTR) reuse (fd));
}
}
/* We start off with the malloc descriptor allocated on the stack, until
we build it up enough to call _mmalloc_mmap_morecore() to allocate the
first page of the region and copy it there. Ensure that it is zero'd and
then initialize the fields that we know values for. */
mdp = &mtemp;
(void) memset ((char *) mdp, 0, sizeof (mtemp));
(void) strncpy (mdp -> magic, MMALLOC_MAGIC, MMALLOC_MAGIC_SIZE);
mdp -> headersize = sizeof (mtemp);
mdp -> version = MMALLOC_VERSION;
mdp -> morecore = __mmalloc_mmap_morecore;
mdp -> fd = fd;
mdp -> base = mdp -> breakval = mdp -> top = baseaddr;
/* If we have not been passed a valid open file descriptor for the file
to map to, then open /dev/zero and use that to map to. */
if (mdp -> fd < 0)
{
if ((mdp -> fd = open ("/dev/zero", O_RDWR)) < 0)
{
return (NULL);
}
else
{
mdp -> flags |= MMALLOC_DEVZERO;
}
}
/* Now try to map in the first page, copy the malloc descriptor structure
there, and arrange to return a pointer to this new copy. If the mapping
fails, then close the file descriptor if it was opened by us, and arrange
to return a NULL. */
if ((mbase = mdp -> morecore (mdp, sizeof (mtemp))) != NULL)
{
(void) memcpy (mbase, mdp, sizeof (mtemp));
mdp = (struct mdesc *) mbase;
}
else
{
if (mdp -> flags & MMALLOC_DEVZERO)
{
close (mdp -> fd);
}
mdp = NULL;
}
return ((PTR) mdp);
}
/* Given an valid file descriptor on an open file, test to see if that file
is a valid mmalloc produced file, and if so, attempt to remap it into the
current process at the same address to which it was previously mapped.
Note that we have to update the file descriptor number in the malloc-
descriptor read from the file to match the current valid one, before
trying to map the file in, and again after a successful mapping and
after we've switched over to using the mapped in malloc descriptor
rather than the temporary one on the stack.
Once we've switched over to using the mapped in malloc descriptor, we
have to update the pointer to the morecore function, since it almost
certainly will be at a different address if the process reusing the
mapped region is from a different executable.
Also note that if the heap being remapped previously used the mmcheck()
routines, we need to update the hooks since their target functions
will have certainly moved if the executable has changed in any way.
We do this by calling mmcheck() internally.
Returns a pointer to the malloc descriptor if successful, or NULL if
unsuccessful for some reason. */
static struct mdesc *
reuse (fd)
int fd;
{
struct mdesc mtemp;
struct mdesc *mdp = NULL;
if ((lseek (fd, 0L, SEEK_SET) == 0) &&
(read (fd, (char *) &mtemp, sizeof (mtemp)) == sizeof (mtemp)) &&
(mtemp.headersize == sizeof (mtemp)) &&
(strcmp (mtemp.magic, MMALLOC_MAGIC) == 0) &&
(mtemp.version <= MMALLOC_VERSION))
{
mtemp.fd = fd;
if (__mmalloc_remap_core (&mtemp) == mtemp.base)
{
mdp = (struct mdesc *) mtemp.base;
mdp -> fd = fd;
mdp -> morecore = __mmalloc_mmap_morecore;
if (mdp -> mfree_hook != NULL)
{
(void) mmcheck ((PTR) mdp, (void (*) PARAMS ((void))) NULL);
}
}
}
return (mdp);
}
#else /* !defined (HAVE_MMAP) */
/* For systems without mmap, the library still supplies an entry point
to link to, but trying to initialize access to an mmap'd managed region
always fails. */
/* ARGSUSED */
PTR
mmalloc_attach (fd, baseaddr)
int fd;
PTR baseaddr;
{
return (NULL);
}
#endif /* defined (HAVE_MMAP) */
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