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109 lines
3.1 KiB
Text
109 lines
3.1 KiB
Text
# Copyright (c) 2011, 2012 Oracle and/or its affiliates. All rights reserved.
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# Detect mmap capability: If the file underlying an mmap is extended,
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# does the addressable memory grow too?
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AC_DEFUN(AM_MMAP_EXTEND, [
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AH_TEMPLATE(HAVE_MMAP_EXTEND, [Define to 1 where mmap() incrementally extends the accessible mapping as the underlying file grows.])
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if test "$mmap_ok" = "yes" ; then
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AC_MSG_CHECKING([for growing a file under an mmap region])
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db_cv_mmap_extend="no"
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AC_TRY_RUN([
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/*
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* Most mmap() implemenations allow you to map in a region which is much
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* larger than the underlying file. Only the second less than the actual
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* file size is accessible -- a SIGSEV typically results when attemping
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* a memory reference between EOF and the end of the mapped region.
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* One can extend the file to allow references into higher-addressed
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* sections of the region. However this automatic extension of the
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* addressible memory is beyond what POSIX requires. This function detects
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* whether mmap supports this automatic extension. If not (e.g. cygwin)
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* then the entire (hopefully sparse) file will need to be written before
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* the first mmap.
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*/
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/* Not all these includes are needed, but the minimal set varies from
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* system to system.
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*/
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#include <stdio.h>
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#include <string.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <sys/mman.h>
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#include <signal.h>
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#define TEST_MMAP_BUFSIZE (16 * 1024)
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#define TEST_MMAP_EXTENDSIZE (16 * 1024 * 1024)
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#ifndef MAP_FAILED
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#define MAP_FAILED (-1)
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#endif
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int catch_sig(sig)
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int sig;
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{
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exit(1);
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}
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main() {
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const char *underlying;
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unsigned gapsize;
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char *base;
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int count, fd, i, mode, open_flags, ret, total_size;
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char buf[TEST_MMAP_BUFSIZE];
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gapsize = 1024;
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underlying = ".mmap_config";
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(void) unlink(underlying);
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open_flags = O_CREAT | O_TRUNC | O_RDWR;
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mode = S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH;
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if ((fd = open(underlying, open_flags, mode)) < 0) {
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perror("open");
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return (1);
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}
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total_size = TEST_MMAP_EXTENDSIZE;
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memset(buf, 0, sizeof(buf));
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if ((count = write(fd, buf, sizeof(buf))) != sizeof(buf)) {
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perror("initial write");
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return (2);
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}
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if ((base = mmap(NULL, total_size,
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PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0)) == MAP_FAILED) {
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perror("mmap");
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return (3);
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}
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/* Extend the file with just 1 byte */
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if (lseek(fd, total_size - 1, SEEK_SET) < 0 ||
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(count = write(fd, buf, 1)) != 1) {
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perror("extending write");
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return (4);
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}
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(void) signal(SIGSEGV, catch_sig);
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(void) signal(SIGBUS, catch_sig);
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for (i = sizeof(buf); i < total_size; i += gapsize)
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base[i] = 'A';
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close(fd);
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(void) unlink(underlying);
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return (0);
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}], [db_cv_mmap_extend="yes"],[db_cv_mmap_extend="no"],[db_cv_mmap_extend="no"])
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if test "$db_cv_mmap_extend" = yes; then
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AC_DEFINE(HAVE_MMAP_EXTEND)
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fi
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AC_MSG_RESULT($db_cv_mmap_extend)
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fi
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])
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