docs/file-share-modes

   1 Rules for opening shared files
   2 ==============================
   3
   4 File is already open, with share set to none:
   5
   6         Can not open again
   7
   8
   9 File is already open for reading, with read share:
  10
  11         Can open for reading only, share must include read (can have write too)
  12
  13
  14 File is already open for reading, with write share:
  15
  16         Can open for writing only, share must include read (can have write too)
  17
  18
  19 File is already open for reading, with read + write share:
  20
  21         Can open for read, writing or both, share must include read (can have write too)
  22
  23
  24 File is already open for writing, with read share:
  25
  26         Can open for reading only, share must include write (can have read too)
  27
  28
  29 File is already open for writing, with write share:
  30
  31         Can open for writing only, share must include write (can have read too)
  32
  33
  34 File is already open for writing, with read + write share:
  35
  36         Can open for reading, writing or both, share must include write (can have read too)
  37
  38
  39 File is already open for reading + writing, with read share:
  40
  41         Can open for reading only, share must be read + write
  42
  43
  44 File is already open for reading + writing, with write share:
  45
  46         Can open for for writing only, share must be read + write
  47
  48
  49 File is already open for reading + writing, with read + write share:
  50
  51         Can open for read, writing or both, share must be read + write
  52
  53
  54
  55 Executive Summary
  56 -----------------
  57
  58         Second open must have access within first share, must set second share to at least first access
  59
  60
  61
  62
  63 Documenting code
  64 ----------------
  65
  66
  67 #include <stdio.h>
  68 #include <windows.h>
  69
  70 int access[] = {
  71         GENERIC_READ,
  72         GENERIC_WRITE,
  73         GENERIC_READ | GENERIC_WRITE
  74 };
  75
  76 char *access_names[] = {
  77         "G_READ",
  78         "G_WRITE",
  79         "G_READ|G_WRITE"
  80 };
  81
  82 int share[] = {
  83         FILE_SHARE_READ,
  84         FILE_SHARE_WRITE,
  85         FILE_SHARE_READ | FILE_SHARE_WRITE
  86 };
  87
  88 char *share_names[] = {
  89         "SHARE_READ",
  90         "SHARE_WRITE",
  91         "SHARE_READ|SHARE_WRITE"
  92 };
  93
  94 void lockfiles(int access1, int share1, int access2, int share2)
  95 {
  96         HANDLE h1, h2;
  97         BOOL ret;
  98
  99         if (access2 == 0 && share2 == 0) {
 100                 printf("\n");
 101                 printf("%22.22s\n%22.22s", access_names[access1], share_names[share1]);
 102         }
 103
 104         h1 = CreateFile("lockedfile",
 105                 access[access1],
 106                 share[share1],
 107                 NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
 108         if (h1 == INVALID_HANDLE_VALUE) {
 109                 printf("Open1 failed: %d\n", GetLastError());
 110                 return;
 111         }
 112
 113         h2 = CreateFile("lockedfile",
 114                 access[access2],
 115                 share[share2],
 116                 NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
 117         if (h2 == INVALID_HANDLE_VALUE) {
 118                 printf(" %4.4s", "");
 119         } else {
 120                 printf(" %4.4s", "OK");
 121                 CloseHandle(h2);
 122         }
 123
 124         CloseHandle(h1);
 125 }
 126
 127 int main(int argc, char **argv)
 128 {
 129         int i, j, k, l;
 130
 131         printf("\t\t\t\t\t\t\tSecond Open\n");
 132         printf("%22.22s G_RE G_RE G_RE G_WR G_WR G_WR G_RW G_RW G_RW\n", "");
 133         printf("%22.22s S_RE S_WR S_RW S_RE S_WR S_RW S_RE S_WR S_RW", "First open --v ");
 134         for (i = 0; i < 3; i++) {
 135                 for (j = 0; j < 3; j++) {
 136                         for (k = 0; k < 3; k++) {
 137                                 for (l = 0; l < 3; l++) {
 138                                         lockfiles(i, j, k, l);
 139                                 }
 140                         }
 141                 }
 142         }
 143
 144         return(0);
 145 }
 146
 147
 148
 149 Code output
 150 -----------
 151
 152                                                         Second Open
 153                        G_RE G_RE G_RE G_WR G_WR G_WR G_RW G_RW G_RW
 154        First open --v  S_RE S_WR S_RW S_RE S_WR S_RW S_RE S_WR S_RW
 155                 G_READ
 156             SHARE_READ   OK        OK
 157                 G_READ
 158            SHARE_WRITE                  OK        OK
 159                 G_READ
 160 SHARE_READ|SHARE_WRITE   OK        OK   OK        OK   OK        OK
 161                G_WRITE
 162             SHARE_READ        OK   OK
 163                G_WRITE
 164            SHARE_WRITE                       OK   OK
 165                G_WRITE
 166 SHARE_READ|SHARE_WRITE        OK   OK        OK   OK        OK   OK
 167         G_READ|G_WRITE
 168             SHARE_READ             OK
 169         G_READ|G_WRITE
 170            SHARE_WRITE                            OK
 171         G_READ|G_WRITE
 172 SHARE_READ|SHARE_WRITE             OK             OK             OK
 173