Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code 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

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  *

  */

 #include "precompiled.hpp"

 #include "classfile/vmSymbols.hpp"

 #include "memory/allocation.inline.hpp"

 #include "memory/resourceArea.hpp"

 #include "oops/oop.inline.hpp"

 #include "os_bsd.inline.hpp"

 #include "runtime/handles.inline.hpp"

 #include "runtime/perfMemory.hpp"

 #include "utilities/exceptions.hpp"

 // put OS-includes here

 # include <sys/types.h>

 # include <sys/mman.h>

 # include <errno.h>

 # include <stdio.h>

 # include <unistd.h>

 # include <sys/stat.h>

 # include <signal.h>

 # include <pwd.h>

 static char* backing_store_file_name = NULL;  // name of the backing store

                                               // file, if successfully created.

 // Standard Memory Implementation Details

 // create the PerfData memory region in standard memory.

 //

 static char* create_standard_memory(size_t size) {

   // allocate an aligned chuck of memory

   char* mapAddress = os::reserve_memory(size);

   if (mapAddress == NULL) {

     return NULL;

   }

   // commit memory

   if (!os::commit_memory(mapAddress, size)) {

     if (PrintMiscellaneous && Verbose) {

       warning("Could not commit PerfData memory\n");

     }

     os::release_memory(mapAddress, size);

     return NULL;

   }

   return mapAddress;

 }

 // delete the PerfData memory region

 //

 static void delete_standard_memory(char* addr, size_t size) {

   // there are no persistent external resources to cleanup for standard

   // memory. since DestroyJavaVM does not support unloading of the JVM,

   // cleanup of the memory resource is not performed. The memory will be

   // reclaimed by the OS upon termination of the process.

   //

   return;

 }

 // save the specified memory region to the given file

 //

 // Note: this function might be called from signal handler (by os::abort()),

 // don't allocate heap memory.

 //

 static void save_memory_to_file(char* addr, size_t size) {

  const char* destfile = PerfMemory::get_perfdata_file_path();

  assert(destfile[0] != '\0', "invalid PerfData file path");

   int result;

   RESTARTABLE(::open(destfile, O_CREAT|O_WRONLY|O_TRUNC, S_IREAD|S_IWRITE),

               result);;

   if (result == OS_ERR) {

     if (PrintMiscellaneous && Verbose) {

       warning("Could not create Perfdata save file: %s: %s\n",

               destfile, strerror(errno));

     }

   } else {

     int fd = result;

     for (size_t remaining = size; remaining > 0;) {

       RESTARTABLE(::write(fd, addr, remaining), result);

       if (result == OS_ERR) {

         if (PrintMiscellaneous && Verbose) {

           warning("Could not write Perfdata save file: %s: %s\n",

                   destfile, strerror(errno));

         }

         break;

       }

       remaining -= (size_t)result;

       addr += result;

     }

     RESTARTABLE(::close(fd), result);

     if (PrintMiscellaneous && Verbose) {

       if (result == OS_ERR) {

         warning("Could not close %s: %s\n", destfile, strerror(errno));

       }

     }

   }

   FREE_C_HEAP_ARRAY(char, destfile, mtInternal);

 }

 // Shared Memory Implementation Details

 // Note: the solaris and bsd shared memory implementation uses the mmap

 // interface with a backing store file to implement named shared memory.

 // Using the file system as the name space for shared memory allows a

 // common name space to be supported across a variety of platforms. It

 // also provides a name space that Java applications can deal with through

 // simple file apis.

 //

 // The solaris and bsd implementations store the backing store file in

 // a user specific temporary directory located in the /tmp file system,

 // which is always a local file system and is sometimes a RAM based file

 // system.

 // return the user specific temporary directory name.

 //

 // the caller is expected to free the allocated memory.

 //

 static char* get_user_tmp_dir(const char* user) {

   const char* tmpdir = os::get_temp_directory();

   const char* perfdir = PERFDATA_NAME;

   size_t nbytes = strlen(tmpdir) + strlen(perfdir) + strlen(user) + 3;

   char* dirname = NEW_C_HEAP_ARRAY(char, nbytes, mtInternal);

   // construct the path name to user specific tmp directory

   snprintf(dirname, nbytes, "%s/%s_%s", tmpdir, perfdir, user);

   return dirname;

 }

 // convert the given file name into a process id. if the file

 // does not meet the file naming constraints, return 0.

 //

 static pid_t filename_to_pid(const char* filename) {

   // a filename that doesn't begin with a digit is not a

   // candidate for conversion.

   //

   if (!isdigit(*filename)) {

     return 0;

   }

   // check if file name can be converted to an integer without

   // any leftover characters.

   //

   char* remainder = NULL;

   errno = 0;

   pid_t pid = (pid_t)strtol(filename, &remainder, 10);

   if (errno != 0) {

     return 0;

   }

   // check for left over characters. If any, then the filename is

   // not a candidate for conversion.

   //

   if (remainder != NULL && *remainder != '\0') {

     return 0;

   }

   // successful conversion, return the pid

   return pid;

 }

 // check if the given path is considered a secure directory for

 // the backing store files. Returns true if the directory exists

 // and is considered a secure location. Returns false if the path

 // is a symbolic link or if an error occurred.

 //

 static bool is_directory_secure(const char* path) {

   struct stat statbuf;

   int result = 0;

   RESTARTABLE(::lstat(path, &statbuf), result);

   if (result == OS_ERR) {

     return false;

   }

   // the path exists, now check it's mode

   if (S_ISLNK(statbuf.st_mode) || !S_ISDIR(statbuf.st_mode)) {

     // the path represents a link or some non-directory file type,

     // which is not what we expected. declare it insecure.

     //

     return false;

   }

   else {

     // we have an existing directory, check if the permissions are safe.

     //

     if ((statbuf.st_mode & (S_IWGRP|S_IWOTH)) != 0) {

       // the directory is open for writing and could be subjected

       // to a symlnk attack. declare it insecure.

       //

       return false;

     }

   }

   return true;

 }

 // return the user name for the given user id

 //

 // the caller is expected to free the allocated memory.

 //

 static char* get_user_name(uid_t uid) {

   struct passwd pwent;

   // determine the max pwbuf size from sysconf, and hardcode

   // a default if this not available through sysconf.

   //

   long bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);

   if (bufsize == -1)

     bufsize = 1024;

   char* pwbuf = NEW_C_HEAP_ARRAY(char, bufsize, mtInternal);

   // POSIX interface to getpwuid_r is used on LINUX

   struct passwd* p;

   int result = getpwuid_r(uid, &pwent, pwbuf, (size_t)bufsize, &p);

   if (result != 0 || p == NULL || p->pw_name == NULL || *(p->pw_name) == '\0') {

     if (PrintMiscellaneous && Verbose) {

       if (result != 0) {

         warning("Could not retrieve passwd entry: %s\n",

                 strerror(result));

       }

       else if (p == NULL) {

         // this check is added to protect against an observed problem

         // with getpwuid_r() on RedHat 9 where getpwuid_r returns 0,

         // indicating success, but has p == NULL. This was observed when

         // inserting a file descriptor exhaustion fault prior to the call

         // getpwuid_r() call. In this case, error is set to the appropriate

         // error condition, but this is undocumented behavior. This check

         // is safe under any condition, but the use of errno in the output

         // message may result in an erroneous message.

         // Bug Id 89052 was opened with RedHat.

         //

         warning("Could not retrieve passwd entry: %s\n",

                 strerror(errno));

       }

       else {

         warning("Could not determine user name: %s\n",

                 p->pw_name == NULL ? "pw_name = NULL" :

                                      "pw_name zero length");

       }

     }

     FREE_C_HEAP_ARRAY(char, pwbuf, mtInternal);

     return NULL;

   }

   char* user_name = NEW_C_HEAP_ARRAY(char, strlen(p->pw_name) + 1, mtInternal);

   strcpy(user_name, p->pw_name);

   FREE_C_HEAP_ARRAY(char, pwbuf, mtInternal);

   return user_name;

 }

 // return the name of the user that owns the process identified by vmid.

 //

 // This method uses a slow directory search algorithm to find the backing

 // store file for the specified vmid and returns the user name, as determined

 // by the user name suffix of the hsperfdata_<username> directory name.

 //

 // the caller is expected to free the allocated memory.

 //

 static char* get_user_name_slow(int vmid, TRAPS) {

   // short circuit the directory search if the process doesn't even exist.

   if (kill(vmid, 0) == OS_ERR) {

     if (errno == ESRCH) {

       THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(),

                   "Process not found");

     }

     else /* EPERM */ {

       THROW_MSG_0(vmSymbols::java_io_IOException(), strerror(errno));

     }

   }

   // directory search

   char* oldest_user = NULL;

   time_t oldest_ctime = 0;

   const char* tmpdirname = os::get_temp_directory();

   DIR* tmpdirp = os::opendir(tmpdirname);

   if (tmpdirp == NULL) {

     return NULL;

   }

   // for each entry in the directory that matches the pattern hsperfdata_*,

   // open the directory and check if the file for the given vmid exists.

   // The file with the expected name and the latest creation date is used

   // to determine the user name for the process id.

   //

   struct dirent* dentry;

   char* tdbuf = NEW_C_HEAP_ARRAY(char, os::readdir_buf_size(tmpdirname), mtInternal);

   errno = 0;

   while ((dentry = os::readdir(tmpdirp, (struct dirent *)tdbuf)) != NULL) {

     // check if the directory entry is a hsperfdata file

     if (strncmp(dentry->d_name, PERFDATA_NAME, strlen(PERFDATA_NAME)) != 0) {

       continue;

     }

     char* usrdir_name = NEW_C_HEAP_ARRAY(char,

                  strlen(tmpdirname) + strlen(dentry->d_name) + 2, mtInternal);

     strcpy(usrdir_name, tmpdirname);

     strcat(usrdir_name, "/");

     strcat(usrdir_name, dentry->d_name);

     DIR* subdirp = os::opendir(usrdir_name);

     if (subdirp == NULL) {

       FREE_C_HEAP_ARRAY(char, usrdir_name, mtInternal);

       continue;

     }

     // Since we don't create the backing store files in directories

     // pointed to by symbolic links, we also don't follow them when

     // looking for the files. We check for a symbolic link after the

     // call to opendir in order to eliminate a small window where the

     // symlink can be exploited.

     //

     if (!is_directory_secure(usrdir_name)) {

       FREE_C_HEAP_ARRAY(char, usrdir_name, mtInternal);

       os::closedir(subdirp);

       continue;

     }

     struct dirent* udentry;

     char* udbuf = NEW_C_HEAP_ARRAY(char, os::readdir_buf_size(usrdir_name), mtInternal);

     errno = 0;

     while ((udentry = os::readdir(subdirp, (struct dirent *)udbuf)) != NULL) {

       if (filename_to_pid(udentry->d_name) == vmid) {

         struct stat statbuf;

         int result;

         char* filename = NEW_C_HEAP_ARRAY(char,

                  strlen(usrdir_name) + strlen(udentry->d_name) + 2, mtInternal);

         strcpy(filename, usrdir_name);

         strcat(filename, "/");

         strcat(filename, udentry->d_name);

         // don't follow symbolic links for the file

         RESTARTABLE(::lstat(filename, &statbuf), result);

         if (result == OS_ERR) {

            FREE_C_HEAP_ARRAY(char, filename, mtInternal);

            continue;

         }

         // skip over files that are not regular files.

         if (!S_ISREG(statbuf.st_mode)) {

           FREE_C_HEAP_ARRAY(char, filename, mtInternal);

           continue;

         }

         // compare and save filename with latest creation time

         if (statbuf.st_size > 0 && statbuf.st_ctime > oldest_ctime) {

           if (statbuf.st_ctime > oldest_ctime) {

             char* user = strchr(dentry->d_name, '_') + 1;

             if (oldest_user != NULL) FREE_C_HEAP_ARRAY(char, oldest_user, mtInternal);

             oldest_user = NEW_C_HEAP_ARRAY(char, strlen(user)+1, mtInternal);

             strcpy(oldest_user, user);

             oldest_ctime = statbuf.st_ctime;

           }

         }

         FREE_C_HEAP_ARRAY(char, filename, mtInternal);

       }

     }

     os::closedir(subdirp);

     FREE_C_HEAP_ARRAY(char, udbuf, mtInternal);

     FREE_C_HEAP_ARRAY(char, usrdir_name, mtInternal);

   }

   os::closedir(tmpdirp);

   FREE_C_HEAP_ARRAY(char, tdbuf, mtInternal);

   return(oldest_user);

 }

 // return the name of the user that owns the JVM indicated by the given vmid.

 //

 static char* get_user_name(int vmid, TRAPS) {

   return get_user_name_slow(vmid, CHECK_NULL);

 }

 // return the file name of the backing store file for the named

 // shared memory region for the given user name and vmid.

 //

 // the caller is expected to free the allocated memory.

 //

 static char* get_sharedmem_filename(const char* dirname, int vmid) {

   // add 2 for the file separator and a null terminator.

   size_t nbytes = strlen(dirname) + UINT_CHARS + 2;

   char* name = NEW_C_HEAP_ARRAY(char, nbytes, mtInternal);

   snprintf(name, nbytes, "%s/%d", dirname, vmid);

   return name;

 }

 // remove file

 //

 // this method removes the file specified by the given path

 //

 static void remove_file(const char* path) {

   int result;

   // if the file is a directory, the following unlink will fail. since

   // we don't expect to find directories in the user temp directory, we

   // won't try to handle this situation. even if accidentially or

   // maliciously planted, the directory's presence won't hurt anything.

   //

   RESTARTABLE(::unlink(path), result);

   if (PrintMiscellaneous && Verbose && result == OS_ERR) {

     if (errno != ENOENT) {

       warning("Could not unlink shared memory backing"

               " store file %s : %s\n", path, strerror(errno));

     }

   }

 }

 // remove file

 //

 // this method removes the file with the given file name in the

 // named directory.

 //

 static void remove_file(const char* dirname, const char* filename) {

   size_t nbytes = strlen(dirname) + strlen(filename) + 2;

   char* path = NEW_C_HEAP_ARRAY(char, nbytes, mtInternal);

   strcpy(path, dirname);

   strcat(path, "/");

   strcat(path, filename);

   remove_file(path);

   FREE_C_HEAP_ARRAY(char, path, mtInternal);

 }

 // cleanup stale shared memory resources

 //

 // This method attempts to remove all stale shared memory files in

 // the named user temporary directory. It scans the named directory

 // for files matching the pattern ^$[0-9]*$. For each file found, the

 // process id is extracted from the file name and a test is run to

 // determine if the process is alive. If the process is not alive,

 // any stale file resources are removed.

 //

 static void cleanup_sharedmem_resources(const char* dirname) {

   // open the user temp directory

   DIR* dirp = os::opendir(dirname);

   if (dirp == NULL) {

     // directory doesn't exist, so there is nothing to cleanup

     return;

   }

   if (!is_directory_secure(dirname)) {

     // the directory is not a secure directory

     return;

   }

   // for each entry in the directory that matches the expected file

   // name pattern, determine if the file resources are stale and if

   // so, remove the file resources. Note, instrumented HotSpot processes

   // for this user may start and/or terminate during this search and

   // remove or create new files in this directory. The behavior of this

   // loop under these conditions is dependent upon the implementation of

   // opendir/readdir.

   //

   struct dirent* entry;

   char* dbuf = NEW_C_HEAP_ARRAY(char, os::readdir_buf_size(dirname), mtInternal);

   errno = 0;

   while ((entry = os::readdir(dirp, (struct dirent *)dbuf)) != NULL) {

     pid_t pid = filename_to_pid(entry->d_name);

     if (pid == 0) {

       if (strcmp(entry->d_name, ".") != 0 && strcmp(entry->d_name, "..") != 0) {

         // attempt to remove all unexpected files, except "." and ".."

         remove_file(dirname, entry->d_name);

       }

       errno = 0;

       continue;

     }

     // we now have a file name that converts to a valid integer

     // that could represent a process id . if this process id

     // matches the current process id or the process is not running,

     // then remove the stale file resources.

     //

     // process liveness is detected by sending signal number 0 to

     // the process id (see kill(2)). if kill determines that the

     // process does not exist, then the file resources are removed.

     // if kill determines that that we don't have permission to

     // signal the process, then the file resources are assumed to

     // be stale and are removed because the resources for such a

     // process should be in a different user specific directory.

     //

     if ((pid == os::current_process_id()) ||

         (kill(pid, 0) == OS_ERR && (errno == ESRCH || errno == EPERM))) {

         remove_file(dirname, entry->d_name);

     }

     errno = 0;

   }

   os::closedir(dirp);

   FREE_C_HEAP_ARRAY(char, dbuf, mtInternal);

 }

 // make the user specific temporary directory. Returns true if

 // the directory exists and is secure upon return. Returns false

 // if the directory exists but is either a symlink, is otherwise

 // insecure, or if an error occurred.

 //

 static bool make_user_tmp_dir(const char* dirname) {

   // create the directory with 0755 permissions. note that the directory

   // will be owned by euid::egid, which may not be the same as uid::gid.

   //

   if (mkdir(dirname, S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH) == OS_ERR) {

     if (errno == EEXIST) {

       // The directory already exists and was probably created by another

       // JVM instance. However, this could also be the result of a

       // deliberate symlink. Verify that the existing directory is safe.

       //

       if (!is_directory_secure(dirname)) {

         // directory is not secure

         if (PrintMiscellaneous && Verbose) {

           warning("%s directory is insecure\n", dirname);

         }

         return false;

       }

     }

     else {

       // we encountered some other failure while attempting

       // to create the directory

       //

       if (PrintMiscellaneous && Verbose) {

         warning("could not create directory %s: %s\n",

                 dirname, strerror(errno));

       }

       return false;

     }

   }

   return true;

 }

 // create the shared memory file resources

 //

 // This method creates the shared memory file with the given size

 // This method also creates the user specific temporary directory, if

 // it does not yet exist.

 //

 static int create_sharedmem_resources(const char* dirname, const char* filename, size_t size) {

   // make the user temporary directory

   if (!make_user_tmp_dir(dirname)) {

     // could not make/find the directory or the found directory

     // was not secure

     return -1;

   }

   int result;

   RESTARTABLE(::open(filename, O_RDWR|O_CREAT|O_TRUNC, S_IREAD|S_IWRITE), result);

   if (result == OS_ERR) {

     if (PrintMiscellaneous && Verbose) {

       warning("could not create file %s: %s\n", filename, strerror(errno));

     }

     return -1;

   }

   // save the file descriptor

   int fd = result;

   // set the file size

   RESTARTABLE(::ftruncate(fd, (off_t)size), result);

   if (result == OS_ERR) {

     if (PrintMiscellaneous && Verbose) {

       warning("could not set shared memory file size: %s\n", strerror(errno));

     }

     RESTARTABLE(::close(fd), result);

     return -1;

   }

   // Verify that we have enough disk space for this file.

   // We'll get random SIGBUS crashes on memory accesses if

   // we don't.

   for (size_t seekpos = 0; seekpos < size; seekpos += os::vm_page_size()) {

     int zero_int = 0;

     result = (int)os::seek_to_file_offset(fd, (jlong)(seekpos));

     if (result == -1 ) break;

     RESTARTABLE(::write(fd, &zero_int, 1), result);

     if (result != 1) {

       if (errno == ENOSPC) {

         warning("Insufficient space for shared memory file:\n   %s\nTry using the -Djava.io.tmpdir= option to select an alternate temp location.\n", filename);

       }

       break;

     }

   }

   if (result != -1) {

     return fd;

   } else {

     RESTARTABLE(::close(fd), result);

     return -1;

   }

 }

 // open the shared memory file for the given user and vmid. returns

 // the file descriptor for the open file or -1 if the file could not

 // be opened.

 //

 static int open_sharedmem_file(const char* filename, int oflags, TRAPS) {

   // open the file

   int result;

   RESTARTABLE(::open(filename, oflags), result);

   if (result == OS_ERR) {

     if (errno == ENOENT) {

       THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(),

                   "Process not found");

     }

     else if (errno == EACCES) {

       THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(),

                   "Permission denied");

     }

     else {

       THROW_MSG_0(vmSymbols::java_io_IOException(), strerror(errno));

     }

   }

   return result;

 }

 // create a named shared memory region. returns the address of the

 // memory region on success or NULL on failure. A return value of

 // NULL will ultimately disable the shared memory feature.

 //

 // On Solaris and Bsd, the name space for shared memory objects

 // is the file system name space.

 //

 // A monitoring application attaching to a JVM does not need to know

 // the file system name of the shared memory object. However, it may

 // be convenient for applications to discover the existence of newly

 // created and terminating JVMs by watching the file system name space

 // for files being created or removed.

 //

 static char* mmap_create_shared(size_t size) {

   int result;

   int fd;

   char* mapAddress;

   int vmid = os::current_process_id();

   char* user_name = get_user_name(geteuid());

   if (user_name == NULL)

     return NULL;

   char* dirname = get_user_tmp_dir(user_name);

   char* filename = get_sharedmem_filename(dirname, vmid);

   // cleanup any stale shared memory files

   cleanup_sharedmem_resources(dirname);

   assert(((size > 0) && (size % os::vm_page_size() == 0)),

          "unexpected PerfMemory region size");

   fd = create_sharedmem_resources(dirname, filename, size);

   FREE_C_HEAP_ARRAY(char, user_name, mtInternal);

   FREE_C_HEAP_ARRAY(char, dirname, mtInternal);

   if (fd == -1) {

     FREE_C_HEAP_ARRAY(char, filename, mtInternal);

     return NULL;

   }

   mapAddress = (char*)::mmap((char*)0, size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);

   // attempt to close the file - restart it if it was interrupted,

   // but ignore other failures

   RESTARTABLE(::close(fd), result);

   assert(result != OS_ERR, "could not close file");

   if (mapAddress == MAP_FAILED) {

     if (PrintMiscellaneous && Verbose) {

       warning("mmap failed -  %s\n", strerror(errno));

     }

     remove_file(filename);

     FREE_C_HEAP_ARRAY(char, filename, mtInternal);

     return NULL;

   }

   // save the file name for use in delete_shared_memory()

   backing_store_file_name = filename;

   // clear the shared memory region

   (void)::memset((void*) mapAddress, 0, size);

   return mapAddress;

 }

 // release a named shared memory region

 //

 static void unmap_shared(char* addr, size_t bytes) {

   os::release_memory(addr, bytes);

 }

 // create the PerfData memory region in shared memory.

 //

 static char* create_shared_memory(size_t size) {

   // create the shared memory region.

   return mmap_create_shared(size);

 }

 // delete the shared PerfData memory region

 //

 static void delete_shared_memory(char* addr, size_t size) {

   // cleanup the persistent shared memory resources. since DestroyJavaVM does

   // not support unloading of the JVM, unmapping of the memory resource is

   // not performed. The memory will be reclaimed by the OS upon termination of

   // the process. The backing store file is deleted from the file system.

   assert(!PerfDisableSharedMem, "shouldn't be here");

   if (backing_store_file_name != NULL) {

     remove_file(backing_store_file_name);

     // Don't.. Free heap memory could deadlock os::abort() if it is called

     // from signal handler. OS will reclaim the heap memory.

     // FREE_C_HEAP_ARRAY(char, backing_store_file_name);

     backing_store_file_name = NULL;

   }

 }

 // return the size of the file for the given file descriptor

 // or 0 if it is not a valid size for a shared memory file

 //

 static size_t sharedmem_filesize(int fd, TRAPS) {

   struct stat statbuf;

   int result;

   RESTARTABLE(::fstat(fd, &statbuf), result);

   if (result == OS_ERR) {

     if (PrintMiscellaneous && Verbose) {

       warning("fstat failed: %s\n", strerror(errno));

     }

     THROW_MSG_0(vmSymbols::java_io_IOException(),

                 "Could not determine PerfMemory size");

   }

   if ((statbuf.st_size == 0) ||

      ((size_t)statbuf.st_size % os::vm_page_size() != 0)) {

     THROW_MSG_0(vmSymbols::java_lang_Exception(),

                 "Invalid PerfMemory size");

   }

   return (size_t)statbuf.st_size;

 }

 // attach to a named shared memory region.

 //

 static void mmap_attach_shared(const char* user, int vmid, PerfMemory::PerfMemoryMode mode, char** addr, size_t* sizep, TRAPS) {

   char* mapAddress;

   int result;

   int fd;

   size_t size;

   const char* luser = NULL;

   int mmap_prot;

   int file_flags;

   ResourceMark rm;

   // map the high level access mode to the appropriate permission

   // constructs for the file and the shared memory mapping.

   if (mode == PerfMemory::PERF_MODE_RO) {

     mmap_prot = PROT_READ;

     file_flags = O_RDONLY;

   }

   else if (mode == PerfMemory::PERF_MODE_RW) {

 #ifdef LATER

     mmap_prot = PROT_READ | PROT_WRITE;

     file_flags = O_RDWR;

 #else

     THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(),

               "Unsupported access mode");

 #endif

   }

   else {

     THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(),

               "Illegal access mode");

   }

   if (user == NULL || strlen(user) == 0) {

     luser = get_user_name(vmid, CHECK);

   }

   else {

     luser = user;

   }

   if (luser == NULL) {

     THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(),

               "Could not map vmid to user Name");

   }

   char* dirname = get_user_tmp_dir(luser);

   // since we don't follow symbolic links when creating the backing

   // store file, we don't follow them when attaching either.

   //

   if (!is_directory_secure(dirname)) {

     FREE_C_HEAP_ARRAY(char, dirname, mtInternal);

     THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(),

               "Process not found");

   }

   char* filename = get_sharedmem_filename(dirname, vmid);

   // copy heap memory to resource memory. the open_sharedmem_file

   // method below need to use the filename, but could throw an

   // exception. using a resource array prevents the leak that

   // would otherwise occur.

   char* rfilename = NEW_RESOURCE_ARRAY(char, strlen(filename) + 1);

   strcpy(rfilename, filename);

   // free the c heap resources that are no longer needed

   if (luser != user) FREE_C_HEAP_ARRAY(char, luser, mtInternal);

   FREE_C_HEAP_ARRAY(char, dirname, mtInternal);

   FREE_C_HEAP_ARRAY(char, filename, mtInternal);

   // open the shared memory file for the give vmid

   fd = open_sharedmem_file(rfilename, file_flags, CHECK);

   assert(fd != OS_ERR, "unexpected value");

   if (*sizep == 0) {

     size = sharedmem_filesize(fd, CHECK);

     assert(size != 0, "unexpected size");

   }

   mapAddress = (char*)::mmap((char*)0, size, mmap_prot, MAP_SHARED, fd, 0);

   // attempt to close the file - restart if it gets interrupted,

   // but ignore other failures

   RESTARTABLE(::close(fd), result);

   assert(result != OS_ERR, "could not close file");

   if (mapAddress == MAP_FAILED) {

     if (PrintMiscellaneous && Verbose) {

       warning("mmap failed: %s\n", strerror(errno));

     }

     THROW_MSG(vmSymbols::java_lang_OutOfMemoryError(),

               "Could not map PerfMemory");

   }

   *addr = mapAddress;

   *sizep = size;

   if (PerfTraceMemOps) {

     tty->print("mapped " SIZE_FORMAT " bytes for vmid %d at "

                INTPTR_FORMAT "\n", size, vmid, (void*)mapAddress);

   }

 }

 // create the PerfData memory region

 //

 // This method creates the memory region used to store performance

 // data for the JVM. The memory may be created in standard or

 // shared memory.

 //

 void PerfMemory::create_memory_region(size_t size) {

   if (PerfDisableSharedMem) {

     // do not share the memory for the performance data.

     _start = create_standard_memory(size);

   }

   else {

     _start = create_shared_memory(size);

     if (_start == NULL) {

       // creation of the shared memory region failed, attempt

       // to create a contiguous, non-shared memory region instead.

       //

       if (PrintMiscellaneous && Verbose) {

         warning("Reverting to non-shared PerfMemory region.\n");

       }

       PerfDisableSharedMem = true;

       _start = create_standard_memory(size);

     }

   }

   if (_start != NULL) _capacity = size;

 }

 // delete the PerfData memory region

 //

 // This method deletes the memory region used to store performance

 // data for the JVM. The memory region indicated by the <address, size>

 // tuple will be inaccessible after a call to this method.

 //

 void PerfMemory::delete_memory_region() {

   assert((start() != NULL && capacity() > 0), "verify proper state");

   // If user specifies PerfDataSaveFile, it will save the performance data

   // to the specified file name no matter whether PerfDataSaveToFile is specified

   // or not. In other word, -XX:PerfDataSaveFile=.. overrides flag

   // -XX:+PerfDataSaveToFile.

   if (PerfDataSaveToFile || PerfDataSaveFile != NULL) {

     save_memory_to_file(start(), capacity());

   }

   if (PerfDisableSharedMem) {

     delete_standard_memory(start(), capacity());

   }

   else {

     delete_shared_memory(start(), capacity());

   }

 }

 // attach to the PerfData memory region for another JVM

 //

 // This method returns an <address, size> tuple that points to

 // a memory buffer that is kept reasonably synchronized with

 // the PerfData memory region for the indicated JVM. This

 // buffer may be kept in synchronization via shared memory

 // or some other mechanism that keeps the buffer updated.

 //

 // If the JVM chooses not to support the attachability feature,

 // this method should throw an UnsupportedOperation exception.

 //

 // This implementation utilizes named shared memory to map

 // the indicated process's PerfData memory region into this JVMs

 // address space.

 //

 void PerfMemory::attach(const char* user, int vmid, PerfMemoryMode mode, char** addrp, size_t* sizep, TRAPS) {

   if (vmid == 0 || vmid == os::current_process_id()) {

      *addrp = start();

      *sizep = capacity();

      return;

   }

   mmap_attach_shared(user, vmid, mode, addrp, sizep, CHECK);

 }

 // detach from the PerfData memory region of another JVM

 //

 // This method detaches the PerfData memory region of another

 // JVM, specified as an <address, size> tuple of a buffer

 // in this process's address space. This method may perform

 // arbitrary actions to accomplish the detachment. The memory

 // region specified by <address, size> will be inaccessible after

 // a call to this method.

 //

 // If the JVM chooses not to support the attachability feature,

 // this method should throw an UnsupportedOperation exception.

 //

 // This implementation utilizes named shared memory to detach

 // the indicated process's PerfData memory region from this

 // process's address space.

 //

 void PerfMemory::detach(char* addr, size_t bytes, TRAPS) {

   assert(addr != 0, "address sanity check");

   assert(bytes > 0, "capacity sanity check");

   if (PerfMemory::contains(addr) || PerfMemory::contains(addr + bytes - 1)) {

     // prevent accidental detachment of this process's PerfMemory region

     return;

   }

   unmap_shared(addr, bytes);

 }

 char* PerfMemory::backing_store_filename() {

   return backing_store_file_name;

 }