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sqlite3

    1: /*
    2: ** This utility program looks at an SQLite database and determines whether
    3: ** or not it is locked, the kind of lock, and who is holding this lock.
    4: **
    5: ** This only works on unix when the posix advisory locking method is used
    6: ** (which is the default on unix) and when the PENDING_BYTE is in its
    7: ** usual place.
    8: */
    9: #include <sys/types.h>
   10: #include <sys/stat.h>
   11: #include <unistd.h>
   12: #include <fcntl.h>
   13: #include <string.h>
   14: #include <stdio.h>
   15: #include <stdlib.h>
   16: #include <errno.h>
   17: 
   18: static void usage(const char *argv0){
   19:   fprintf(stderr, "Usage: %s database\n", argv0);
   20:   exit(1);
   21: }
   22: 
   23: /* Check for a conflicting lock.  If one is found, print an this
   24: ** on standard output using the format string given and return 1.
   25: ** If there are no conflicting locks, return 0.
   26: */
   27: static int isLocked(
   28:   int h,                /* File descriptor to check */
   29:   int type,             /* F_RDLCK or F_WRLCK */
   30:   unsigned int iOfst,   /* First byte of the lock */
   31:   unsigned int iCnt,    /* Number of bytes in the lock range */
   32:   const char *zType     /* Type of lock */
   33: ){
   34:   struct flock lk;
   35: 
   36:   memset(&lk, 0, sizeof(lk));
   37:   lk.l_type = type;
   38:   lk.l_whence = SEEK_SET;
   39:   lk.l_start = iOfst;
   40:   lk.l_len = iCnt;
   41:   if( fcntl(h, F_GETLK, &lk)==(-1) ){
   42:     fprintf(stderr, "fcntl(%d) failed: errno=%d\n", h, errno);
   43:     exit(1);
   44:   }
   45:   if( lk.l_type==F_UNLCK ) return 0;
   46:   printf("%s lock held by %d\n", zType, (int)lk.l_pid);
   47:   return 1;
   48: }
   49: 
   50: /*
   51: ** Location of locking bytes in the database file
   52: */
   53: #define PENDING_BYTE      (0x40000000)
   54: #define RESERVED_BYTE     (PENDING_BYTE+1)
   55: #define SHARED_FIRST      (PENDING_BYTE+2)
   56: #define SHARED_SIZE       510
   57: 
   58: /*
   59: ** Lock locations for shared-memory locks used by WAL mode.
   60: */
   61: #define SHM_BASE          120
   62: #define SHM_WRITE         SHM_BASE
   63: #define SHM_CHECKPOINT    (SHM_BASE+1)
   64: #define SHM_RECOVER       (SHM_BASE+2)
   65: #define SHM_READ_FIRST    (SHM_BASE+3)
   66: #define SHM_READ_SIZE     5
   67: 
   68: 
   69: int main(int argc, char **argv){
   70:   int hDb;        /* File descriptor for the open database file */
   71:   int hShm;       /* File descriptor for WAL shared-memory file */
   72:   char *zShm;     /* Name of the shared-memory file for WAL mode */
   73:   ssize_t got;    /* Bytes read from header */
   74:   int isWal;                 /* True if in WAL mode */
   75:   int nName;                 /* Length of filename */
   76:   unsigned char aHdr[100];   /* Database header */
   77:   int nLock = 0;             /* Number of locks held */
   78:   int i;                     /* Loop counter */
   79: 
   80:   if( argc!=2 ) usage(argv[0]);
   81:   hDb = open(argv[1], O_RDONLY, 0);
   82:   if( hDb<0 ){
   83:     fprintf(stderr, "cannot open %s\n", argv[1]);
   84:     return 1;
   85:   }
   86: 
   87:   /* Make sure we are dealing with an database file */
   88:   got = read(hDb, aHdr, 100);
   89:   if( got!=100 || memcmp(aHdr, "SQLite format 3",16)!=0 ){
   90:     fprintf(stderr, "not an SQLite database: %s\n", argv[1]);
   91:     exit(1);
   92:   }
   93: 
   94:   /* First check for an exclusive lock */
   95:   if( isLocked(hDb, F_RDLCK, SHARED_FIRST, SHARED_SIZE, "EXCLUSIVE") ){
   96:     return 0;
   97:   }
   98:   isWal = aHdr[18]==2;
   99:   if( isWal==0 ){
  100:     /* Rollback mode */
  101:     if( isLocked(hDb, F_RDLCK, PENDING_BYTE, 1, "PENDING") ) return 0;
  102:     if( isLocked(hDb, F_RDLCK, RESERVED_BYTE, 1, "RESERVED") ) return 0;
  103:     if( isLocked(hDb, F_WRLCK, SHARED_FIRST, SHARED_SIZE, "SHARED") ){
  104:       return 0;
  105:     }
  106:   }else{
  107:     /* WAL mode */
  108:     nName = (int)strlen(argv[1]);
  109:     zShm = malloc( nName + 100 );
  110:     if( zShm==0 ){
  111:       fprintf(stderr, "out of memory\n");
  112:       exit(1);
  113:     }
  114:     memcpy(zShm, argv[1], nName);
  115:     memcpy(&zShm[nName], "-shm", 5);
  116:     hShm = open(zShm, O_RDONLY, 0);
  117:     if( hShm<0 ){
  118:       fprintf(stderr, "cannot open %s\n", zShm);
  119:       return 1;
  120:     }
  121:     if( isLocked(hShm, F_RDLCK, SHM_RECOVER, 1, "WAL-RECOVERY") ){
  122:       return 0;
  123:     }
  124:     nLock += isLocked(hShm, F_RDLCK, SHM_CHECKPOINT, 1, "WAL-CHECKPOINT");
  125:     nLock += isLocked(hShm, F_RDLCK, SHM_WRITE, 1, "WAL-WRITE");
  126:     for(i=0; i<SHM_READ_SIZE; i++){
  127:       nLock += isLocked(hShm, F_WRLCK, SHM_READ_FIRST+i, 1, "WAL-READ");
  128:     }
  129:   }
  130:   if( nLock==0 ){
  131:     printf("file is not locked\n");
  132:   }
  133:   return 0;
  134: }