#include <sys/wait.h>
#include <ucontext.h>
-//extern declaration definition
#define FAILURE(mesg) { printf("failed in the API: %s with errno relative message: %s\n", mesg, strerror( errno ) ); exit(EXIT_FAILURE); }
+
+#ifdef CONFIG_SSDEBUG
+#define SSDEBUG printf
+#else
+#define SSDEBUG(...) do { } while (0)
+#endif
+
+/* extern declaration definition */
#if USE_MPROTECT_SNAPSHOT
struct SnapShot * snapshotrecord = NULL;
-struct Snapshot_t * sTheRecord = NULL;
#else
-struct Snapshot_t * sTheRecord = NULL;
+struct Snapshot * sTheRecord = NULL;
#endif
-void DumpIntoLog( const char * filename, const char * message ){
-#if SSDEBUG
- static pid_t thePID = getpid();
- char newFn[ 1024 ] ={ 0 };
- sprintf( newFn,"%s-%d.txt", filename, thePID );
- FILE * myFile = fopen( newFn, "w+" );
- fprintf( myFile, "the message %s: the process id %d\n", message, thePID );
- fflush( myFile );
- fclose( myFile );
- myFile = NULL;
-#endif
-}
+
#if !USE_MPROTECT_SNAPSHOT
+/** @statics
+* These variables are necessary because the stack is shared region and
+* there exists a race between all processes executing the same function.
+* To avoid the problem above, we require variables allocated in 'safe' regions.
+* The bug was actually observed with the forkID, these variables below are
+* used to indicate the various contexts to which to switch to.
+*
+* @savedSnapshotContext: contains the point to which takesnapshot() call should switch to.
+* @savedUserSnapshotContext: contains the point to which the process whose snapshotid is equal to the rollbackid should switch to
+* @snapshotid: it is a running counter for the various forked processes snapshotid. it is incremented and set in a persistently shared record
+*/
static ucontext_t savedSnapshotContext;
static ucontext_t savedUserSnapshotContext;
static snapshot_id snapshotid = 0;
#endif
-/* Initialize snapshot data structure */
+
+/** PageAlignedAdressUpdate return a page aligned address for the
+ * address being added as a side effect the numBytes are also changed.
+ */
+static void * PageAlignAddressUpward(void * addr) {
+ return (void *)((((uintptr_t)addr)+PAGESIZE-1)&~(PAGESIZE-1));
+}
+
#if USE_MPROTECT_SNAPSHOT
+/** ReturnPageAlignedAddress returns a page aligned address for the
+ * address being added as a side effect the numBytes are also changed.
+ */
+static void * ReturnPageAlignedAddress(void * addr) {
+ return (void *)(((uintptr_t)addr)&~(PAGESIZE-1));
+}
+
/** The initSnapShotRecord method initialized the snapshotting data
- * structures for the mprotect based snapshot.
+ * structures for the mprotect based snapshot.
*/
-void initSnapShotRecord(unsigned int numbackingpages, unsigned int numsnapshots, unsigned int nummemoryregions) {
+static void initSnapShotRecord(unsigned int numbackingpages, unsigned int numsnapshots, unsigned int nummemoryregions) {
snapshotrecord=( struct SnapShot * )MYMALLOC(sizeof(struct SnapShot));
snapshotrecord->regionsToSnapShot=( struct MemoryRegion * )MYMALLOC(sizeof(struct MemoryRegion)*nummemoryregions);
snapshotrecord->backingStoreBasePtr= ( struct SnapShotPage * )MYMALLOC( sizeof( struct SnapShotPage ) * (numbackingpages + 1) );
snapshotrecord->maxBackingPages=numbackingpages;
snapshotrecord->maxSnapShots=numsnapshots;
}
-#endif //nothing to initialize for the fork based snapshotting.
/** HandlePF is the page fault handler for mprotect based snapshotting
* algorithm.
*/
-
-void HandlePF( int sig, siginfo_t *si, void * unused){
-#if USE_MPROTECT_SNAPSHOT
+static void HandlePF( int sig, siginfo_t *si, void * unused){
if( si->si_code == SEGV_MAPERR ){
printf("Real Fault at %p\n", si->si_addr);
exit( EXIT_FAILURE );
perror("mprotect");
// Handle error by quitting?
}
-#endif //nothing to handle for non snapshotting case.
}
+#endif //nothing to handle for non snapshotting case.
-/** ReturnPageAlignedAddress returns a page aligned address for the
- * address being added as a side effect the numBytes are also changed.
- */
-
-void * ReturnPageAlignedAddress(void * addr) {
- return (void *)(((uintptr_t)addr)&~(PAGESIZE-1));
-}
-
-/** PageAlignedAdressUpdate return a page aligned address for the
- * address being added as a side effect the numBytes are also changed.
- */
-
-void * PageAlignAddressUpward(void * addr) {
- return (void *)((((uintptr_t)addr)+PAGESIZE-1)&~(PAGESIZE-1));
-}
-#ifdef __cplusplus
-extern "C" {
-#endif
- void createSharedLibrary(){
+void createSharedLibrary(){
#if !USE_MPROTECT_SNAPSHOT
- //step 1. create shared memory.
- if( sTheRecord ) return;
- int fd = shm_open( "/ModelChecker-Snapshotter", O_RDWR | O_CREAT, 0777 ); //universal permissions.
- if( -1 == fd ) FAILURE("shm_open");
- if( -1 == ftruncate( fd, ( size_t )SHARED_MEMORY_DEFAULT + ( size_t )STACK_SIZE_DEFAULT ) ) FAILURE( "ftruncate" );
- char * memMapBase = ( char * ) mmap( 0, ( size_t )SHARED_MEMORY_DEFAULT + ( size_t )STACK_SIZE_DEFAULT, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0 );
- if( MAP_FAILED == memMapBase ) FAILURE("mmap");
- sTheRecord = ( struct Snapshot_t * )memMapBase;
- sTheRecord->mSharedMemoryBase = memMapBase + sizeof( struct Snapshot_t );
- sTheRecord->mStackBase = ( char * )memMapBase + ( size_t )SHARED_MEMORY_DEFAULT;
- sTheRecord->mStackSize = STACK_SIZE_DEFAULT;
- sTheRecord->mIDToRollback = -1;
- sTheRecord->currSnapShotID = 0;
- sTheRecord->mbFinalize = false;
+ //step 1. create shared memory.
+ if ( sTheRecord )
+ return;
+ int fd = shm_open( "/ModelChecker-Snapshotter", O_RDWR | O_CREAT, 0777 ); //universal permissions.
+ if ( -1 == fd )
+ FAILURE("shm_open");
+ if ( -1 == ftruncate( fd, SHARED_MEMORY_DEFAULT + STACK_SIZE_DEFAULT ) )
+ FAILURE( "ftruncate" );
+ void * memMapBase = mmap( 0, SHARED_MEMORY_DEFAULT + STACK_SIZE_DEFAULT, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0 );
+ if( MAP_FAILED == memMapBase )
+ FAILURE("mmap");
+ sTheRecord = ( struct Snapshot * )memMapBase;
+ sTheRecord->mSharedMemoryBase = (void *)((uintptr_t)memMapBase + sizeof(struct Snapshot));
+ sTheRecord->mStackBase = (void *)((uintptr_t)memMapBase + SHARED_MEMORY_DEFAULT);
+ sTheRecord->mStackSize = STACK_SIZE_DEFAULT;
+ sTheRecord->mIDToRollback = -1;
+ sTheRecord->currSnapShotID = 0;
#endif
- }
-#ifdef __cplusplus
}
-#endif
/** The initSnapShotLibrary function initializes the Snapshot library.
* @param entryPoint the function that should run the program.
createSharedLibrary();
//step 2 setup the stack context.
-
- int alreadySwapped = 0;
- getcontext( &savedSnapshotContext );
- if( !alreadySwapped ){
- alreadySwapped = 1;
- ucontext_t currentContext, swappedContext, newContext;
- getcontext( &newContext );
- newContext.uc_stack.ss_sp = sTheRecord->mStackBase;
- newContext.uc_stack.ss_size = STACK_SIZE_DEFAULT;
- newContext.uc_link = ¤tContext;
- makecontext( &newContext, entryPoint, 0 );
- swapcontext( &swappedContext, &newContext );
- }
-
- //add the code to take a snapshot here...
- //to return to user process, do a second swapcontext...
+ ucontext_t newContext;
+ getcontext( &newContext );
+ newContext.uc_stack.ss_sp = sTheRecord->mStackBase;
+ newContext.uc_stack.ss_size = STACK_SIZE_DEFAULT;
+ makecontext( &newContext, entryPoint, 0 );
+ /* switch to a new entryPoint context, on a new stack */
+ swapcontext(&savedSnapshotContext, &newContext);
+
+ /* switch back here when takesnapshot is called */
pid_t forkedID = 0;
snapshotid = sTheRecord->currSnapShotID;
bool swapContext = false;
- while( !sTheRecord->mbFinalize ){
+ while( true ){
sTheRecord->currSnapShotID=snapshotid+1;
forkedID = fork();
if( 0 == forkedID ){
ucontext_t currentContext;
-#if 0
- int dbg = 0;
- while( !dbg );
-#endif
+ /*If the rollback bool is set{ see below }, switch to the context we need to return to during a rollback*/
if( swapContext )
swapcontext( ¤tContext, &( sTheRecord->mContextToRollback ) );
else{
+ /*Child process which is forked as a result of takesnapshot call should switch back to the takesnapshot context*/
swapcontext( ¤tContext, &savedUserSnapshotContext );
}
} else {
int status;
int retVal;
-#if SSDEBUG
- char mesg[ 1024 ] = { 0 };
- sprintf( mesg, "The process id of child is %d and the process id of this process is %d and snapshot id is %d", forkedID, getpid(), snapshotid );
- DumpIntoLog( "ModelSnapshot", mesg );
-#endif
+
+ SSDEBUG("The process id of child is %d and the process id of this process is %d and snapshot id is %d",
+ forkedID, getpid(), snapshotid );
+
do {
retVal=waitpid( forkedID, &status, 0 );
} while( -1 == retVal && errno == EINTR );
if( sTheRecord->mIDToRollback != snapshotid )
exit(EXIT_SUCCESS);
else{
+ /*This bool indicates that the current process's snapshotid is same as the id to which the rollback needs to occur*/
swapContext = true;
}
}
#endif
}
-/** The addMemoryRegionToSnapShot function assumes that addr is page aligned.
+/** The addMemoryRegionToSnapShot function assumes that addr is page aligned.
*/
void addMemoryRegionToSnapShot( void * addr, unsigned int numPages) {
#if USE_MPROTECT_SNAPSHOT
/** The takeSnapshot function takes a snapshot.
* @return The snapshot identifier.
*/
-
snapshot_id takeSnapshot( ){
#if USE_MPROTECT_SNAPSHOT
for(unsigned int region=0; region<snapshotrecord->lastRegion;region++) {
/** The rollBack function rollback to the given snapshot identifier.
* @param theID is the snapshot identifier to rollback to.
*/
-
void rollBack( snapshot_id theID ){
#if USE_MPROTECT_SNAPSHOT
std::map< void *, bool, std::less< void * >, MyAlloc< std::pair< const void *, bool > > > duplicateMap;
sTheRecord->mIDToRollback = theID;
int sTemp = 0;
getcontext( &sTheRecord->mContextToRollback );
+ /*
+ * This is used to quit the process on rollback, so that
+ * the process which needs to rollback can quit allowing the process whose snapshotid matches the rollbackid to switch to
+ * this context and continue....
+ */
if( !sTemp ){
sTemp = 1;
-#if SSDEBUG
- DumpIntoLog( "ModelSnapshot", "Invoked rollback" );
-#endif
+ SSDEBUG("Invoked rollback");
exit(EXIT_SUCCESS);
}
-#endif
-}
-
-/** The finalize method shuts down the snapshotting system. */
-//Subramanian -- remove this function from the external interface and
-//have us call it internally
-
-void finalize(){
-#if !USE_MPROTECT_SNAPSHOT
- sTheRecord->mbFinalize = true;
+ /*
+ * This fix obviates the need for a finalize call. hence less dependences for model-checker....
+ *
+ */
+ sTheRecord->mIDToRollback = -1;
#endif
}